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+# Durable Execution on PgQue — Feasibility & Adoption Study
+
+- **Status:** Brainstorm / decision input (not approved scope)
+- **Date:** 2026-05-30
+- **Question:** Should PgQue extend beyond a queue into a **durable-workflow /
+  durable-execution engine on Postgres**, the way DBOS and absurd have? What are
+  the realistic chances of adoption success if we go that route?
+- **Companion reading:** `blueprints/SPECx.md` §2.3 (workflow engines treated as
+  a separate category today), `blueprints/COOPERATIVE_CONSUMERS.md` (0.2,
+  experimental), PR #237 (rotating zero-bloat `send_at`), `CLAUDE.md` Key Design
+  Rules #2 (the PgQ engine is sacred) and #3 (modern API must reduce cleanly to
+  PgQ primitives).
+
+This study was produced after a deep review of the Hacker News thread
+["Building durable workflows on Postgres"](https://news.ycombinator.com/item?id=48313530)
+and a parallel investigation of the six systems that thread orbits around:
+**DBOS, absurd, Temporal, Restate, Rivet, and Gadget's Silo**.
+
+> **Revision note (2026-05-30):** An earlier draft of this study concluded that
+> PgQue's zero-bloat differentiator "does not transfer" to a workflow layer,
+> because durable engines need `SELECT … FOR UPDATE SKIP LOCKED` claim/lease
+> semantics that conflict with PgQ's rotation model. **That conclusion was
+> wrong.** It assumed the DBOS/absurd implementation strategy (a mutable
+> `workflow_status` row updated per step). If instead workflow state transitions
+> are modelled as **appended events over the rotating log** — i.e. durable
+> execution as event sourcing — the rotation model is not an obstacle but an
+> *advantage*. This revision rebuilds the analysis around that architecture.
+
+---
+
+## 1. Verdict up front
+
+**Durable execution is feasible on PgQue's model, and for the workloads that
+dominate today's demand it can win *because of* the model, not despite it.**
+
+The key realisation: durable execution *is* event sourcing (this is literally
+how Temporal's event-history-and-replay works), and PgQ is already an
+append-only event log with snapshot-batched consumption and TRUNCATE rotation.
+The mistake is to copy DBOS/absurd's storage strategy — a mutable
+`workflow_status` row that gets `UPDATE`d on every step — because *that* is what
+bloats, and it is exactly the pattern PgQue exists to avoid. The right strategy
+is to model each workflow as a **stream of state-transition events**: process a
+step, then **enqueue the next state as a new message** rather than mutating a
+row. The workflow is always either (a) one in-flight message, (b) a *scheduled*
+message awaiting a wake time, or (c) terminal. It never holds a batch open
+across a wait, so it never blocks rotation, and every state transition is an
+**append**, not an `UPDATE` — so the zero-bloat property carries straight
+through to the workflow layer.
+
+**What this means for strategy:** the well-leveraged bet is no longer "stay out
+of the workflow category." It is to build an **event-sourced durable-execution
+layer that is rotation-native**, shipped as an optional, experimental
+`pgque-api` layer that reduces to PgQ primitives plus a small bounded
+current-state projection. This stays inside PgQue's identity ("the zero-bloat
+Postgres queue") and turns the engine into a genuine competitive moat for
+high-throughput, fan-out-heavy, short-step durable workflows — precisely the
+AI-agent-loop and event-processing workloads the whole category is currently
+chasing.
+
+**Honest scoping:** the part to defer is *not* the engine — it is the
+"write-it-as-ordinary-linear-code" developer experience (Temporal/DBOS magic
+checkpointing). PgQue's natural programming model is a message-driven state
+machine (closer to AWS Step Functions / actors). That is a DX difference, not a
+capability gap, and it is recoverable later with an SDK that compiles linear
+code into re-enqueued continuations.
+
+Net: **moderate-to-high feasibility**, with a real and defensible
+differentiator — conditional on solving one genuinely hard piece
+(`awaitEvent`/join semantics) and accepting a state-machine programming model
+first, linear-code DX later.
+
+---
+
+## 2. Is the category real? (Yes.)
+
+Durable execution is a funded, growing category, and the "just Postgres"
+variant specifically is where the energy is:
+
+| System | Model | License | Stars (May 2026) | Funding / backing |
+|---|---|---|---|---|
+| **Temporal** | Separate Go cluster, event-sourced replay, Cassandra/MySQL/PG | MIT | ~20.6k | ~$350M total, $1.72B valuation |
+| **DBOS** | Embedded library, Postgres system-DB, checkpoint+replay | MIT (Transact) / proprietary (Conductor) | ~3.5k across 4 SDKs | $8.5M seed; Stonebraker + Zaharia |
+| **absurd** | Single SQL file + thin SDK, SKIP-LOCKED claim/lease, checkpoint-replay | Apache-2.0 | ~1.95k | Armin Ronacher / Earendil |
+| **Restate** | Self-contained Rust binary, RocksDB+log, journaling-replay | BSL 1.1 → Apache | ~3.9k | $7M seed (Redpoint); ex-Flink team |
+| **Rivet** | Actor platform, Postgres/RocksDB/FoundationDB | Apache-2.0 | ~5.6k | YC W23 |
+| **Silo (Gadget)** | Rust broker on SlateDB/object storage | MIT | ~31 (prototype) | Internal Gadget project |
+
+Signals worth internalizing:
+
+- **The market keeps asking "why not just Postgres?"** Restate (own RocksDB
+  store, BSL) took repeated HN criticism on exactly this. Rivet hedged back
+  toward Postgres as a self-host backend. That recurring question *is* PgQue's
+  thesis.
+- **Licensing trust is a real axis.** Restate's BSL drew loud "open source is
+  misleading" criticism; Rivet's Apache-2.0 drew none. PgQue (Apache-2.0,
+  literally "your own Postgres") inherits maximum trust by default.
+- **The wedge against Temporal is operational, not technical.** Every
+  competitor's pitch is the same: *don't run a second distributed system; reuse
+  the database you already operate.* The complaints about Temporal are the
+  determinism learning curve, immutable shard-count decisions, and the
+  Cassandra/Elasticsearch operational floor — not correctness.
+- **AI agents are the current demand driver**, and they are
+  **high-volume, short-step, fan-out-heavy** — the exact workload shape where
+  append+rotate beats update+vacuum (see §5).
+
+So the category is real, PgQue's "Postgres-native, OSI-licensed, no new infra"
+framing is well-aligned with where the market is pulling, *and* — once the
+event-sourced architecture is adopted — PgQue's engine is a substrate advantage
+rather than the liability the first draft assumed.
+
+---
+
+## 3. The architecture: durable execution as event sourcing
+
+### 3.1 The core pattern — continuation-passing over the log
+
+A workflow is a state machine. Each step is a short, independently-triggered
+handler that does its work and **enqueues its successor state as a new event**:
+
+```
+msg {wf: 42, state: charge}  → charge_card();      enqueue {wf:42, state: ship};   ack
+msg {wf: 42, state: ship}    → create_shipment();  enqueue {wf:42, state: notify}; ack
+msg {wf: 42, state: notify}  → notify();           ack          -- terminal
+```
+
+There is no long-running function held in a worker process, so there is nothing
+to "replay" (contrast §3.4). State lives in the event chain (and, for large
+state, in a side row keyed by workflow id; for small state, in the payload
+itself — continuation-passing). Every transition is an **append**. No
+`UPDATE`, no per-step dead tuple, no VACUUM dependence on the hot path.
+
+### 3.2 Exactly-once handoff between steps (PgQue is *stronger* here)
+
+`pgque.insert_event()` (enqueue) and `pgque.finish_batch()` (ack) both run in
+the consumer's own transaction, so a step's effect, its successor enqueue, and
+the batch ack are **one atomic commit**:
+
+```sql
+begin;
+  -- step's own DB side effects (idempotent or in-txn)
+  perform pgque.insert_event(queue, next_state);  -- enqueue successor
+  perform pgque.ack(batch_id);                     -- finish_batch
+commit;
+```
+
+Commit → successor durably enqueued *and* batch finished atomically. Crash
+before commit → txn aborts, no successor exists, the step redelivers cleanly via
+PgQ's normal at-least-once redelivery. This is **exactly-once handoff** — the
+capability DBOS markets as "piggyback the checkpoint in the transaction," except
+here it is literally just SQL in the caller's transaction, and PgQue can
+*demonstrate* it where DBOS documents it only indirectly.
+
+### 3.3 The five durable-execution requirements, on this model
+
+1. **Exclusive ownership — structural, not lease-based.** One logical consumer +
+   cooperative subconsumers (`COOPERATIVE_CONSUMERS.md`, shipping experimental
+   in 0.2). Invariant: **one live message per workflow** (each step enqueues
+   exactly one successor). Each message goes to exactly one subconsumer, so only
+   one worker touches a given workflow at any instant. absurd/DBOS need
+   claim-with-lease + steal-on-crash; PgQue gets exclusivity for free from the
+   single-live-continuation invariant, with the cooperative `dead_interval`
+   takeover already designed for the worker-died-mid-batch case.
+
+2. **Mutable run state — re-enqueue, don't update.** A transition appends a new
+   event carrying the new state. For small state it rides in the payload and
+   there is no long-lived table at all.
+
+3. **Long-lived persistence — PR #237 is the foundation.** A step that sleeps a
+   week acks immediately and enqueues a *scheduled* continuation:
+   `sleep("7 days")` = `send_at(continuation, now()+7d)`. PR #237 makes
+   `send_at` itself **TRUNCATE-rotated and zero-bloat**. A long sleep costs one
+   row in a rotating delayed table — never an open batch, never a vacuum
+   problem. (This dissolves the old "open batch blocks rotation" objection: the
+   workflow does not hold a batch across the wait.)
+
+4. **Per-row scheduling — half solved, half genuinely hard.** Timers/sleep:
+   solved by PR #237's rotating `send_at`. Waking on an **external event**
+   (`awaitEvent`) with a timeout is the real new design work — a small "waiting"
+   registry keyed by `(workflow_id, event_name)`, an `emit` path that injects
+   the continuation, and a maint sweep for timeouts. Low-volume (bounded by
+   in-flight waiters, not throughput), tractable, but it must be designed
+   carefully (first-write-wins event caching to avoid emit/await races — absurd's
+   `e_`/`w_` table pair is a good reference shape).
+
+5. **Checkpoint replay — not needed (see §3.4).**
+
+### 3.4 Why "checkpoint replay" is unnecessary here
+
+In Temporal/DBOS/absurd a workflow is one linear function run in one process; to
+survive a crash, each step's result is saved, and on restart the function is
+**re-run from the top** with completed steps short-circuited from the saved log
+("replay"). That requires a long-lived run owned by a worker for its whole life.
+
+The continuation-passing model **eliminates the concept**: there is no
+long-running function to resume, so nothing to replay. Recovery is just
+redelivery of the single in-flight step, and correctness comes from the
+exactly-once handoff in §3.2 plus per-step idempotency keyed by
+`(workflow_id, step_seq)` (a unique index that prevents double-advance). This is
+strictly simpler than replay and native to a queue.
+
+### 3.5 The one piece of mutable state — bounded by concurrency, not throughput
+
+For observability, addressing, cancellation, and joins, keep a **current-state
+projection**: one row per *live* workflow, replaced as it advances, deleted on
+completion. This is the only mutable table, and it is bounded by **in-flight
+concurrency, not total throughput** — a million finished runs leave zero rows.
+VACUUM load scales with concurrency (fine), not with step volume.
+
+**This split is the whole trick:** hot, high-churn step transitions → rotating
+append-only log (zero bloat); cold, low-volume current-state index → tiny
+mutable table (negligible bloat). DBOS/absurd put the high-churn part on the
+mutable table and inherit the bloat wall; PgQue keeps the high-churn part on the
+log.
+
+---
+
+## 4. What is reusable vs. net-new
+
+**Reusable / already in flight (low cost):**
+
+- **Single-file, anti-extension, managed-PG install** — identical to absurd's
+  validated `absurd.sql` philosophy and PgQue's `\i pgque.sql`.
+- **Cooperative consumers** (0.2) — gives parallel execution + structural
+  per-workflow exclusivity.
+- **Rotating `send_at`** (PR #237) — gives zero-bloat timers/sleep.
+- **Transactional `insert_event` + `finish_batch`** — gives exactly-once handoff
+  with no new primitive.
+- **`jsontriga`** — CDC-triggered workflow starts, native to the engine.
+- **SQL-native observability** — workflows-as-rows/events are `psql`-inspectable.
+
+**Net-new (the real cost, in order of difficulty):**
+
+1. **`awaitEvent` / wait registry + emit path** (§3.3.4) — the genuinely hard
+   design: race-free event caching, timeout sweep, join/fan-in semantics.
+2. **Fan-out / join primitive** — a step that spawns N children (distinct child
+   workflow ids, each independently single-live) and a parent that awaits all N
+   (a counter in the projection, or children emit completion events the parent
+   awaits).
+3. **Current-state projection + step idempotency index** (§3.5) — small, but
+   needs careful transition logic so advance is exactly-once.
+4. **A reference SDK** — *one* language first (Python for AI-agent gravity, or
+   TypeScript for absurd-parity), exposing the state-machine API. Linear-code
+   DX (compiling an `async` function with `await` points into re-enqueued
+   continuations) is a *later* library project, not an engine requirement.
+
+Critically, **none of these touch the PgQ engine** (Rule #2) and all reduce to
+PgQ primitives + a couple of small side tables (Rule #3). The expensive
+multi-language deterministic-replay runtime that dominates DBOS's effort
+**does not exist in this model** — that cost simply isn't incurred.
+
+---
+
+## 5. Adoption analysis — where PgQue wins, and the tradeoffs
+
+### Where PgQue wins *because of* the model
+
+1. **Zero-bloat at high step-throughput — the differentiator now transfers.**
+   DBOS/absurd do `UPDATE workflow_status` + `INSERT operation_outputs` per
+   step: mutable-row churn → the exact bloat wall PgQue exists to defeat. In the
+   event-sourced model every transition is an append to the rotating log; a
+   million agent iterations leave zero dead tuples on the hot path. For the
+   AI-agent-loop-at-scale workload everyone is chasing, **append+rotate
+   structurally beats update+vacuum.** This is the headline.
+2. **Native fan-out + batch step execution.** PgQ hands a *batch* of many
+   workflows' step-events at once, snapshot-isolated — advance thousands of
+   workflows in one transaction. DBOS is 1-write-per-step over per-row
+   `SKIP LOCKED`. PgQue amortizes where they pay per item.
+3. **Transactional exactly-once handoff** (§3.2) — stronger than at-least-once
+   competitors, and just SQL.
+4. **"It's literally just your Postgres"** — no new datastore (vs Restate's
+   RocksDB, Silo's SlateDB, Temporal's Cassandra), Apache-2.0 (vs Restate's
+   BSL), managed-PG compatible. Strongest anti-lock-in story in the field.
+5. **Proven-engine credibility** — PgQ's 15+ years vs absurd's "an experiment in
+   durability" and Silo's self-described prototype.
+
+### The honest tradeoffs
+
+- **State-machine programming model, not magic linear code.** Workflows are
+  expressed as message-driven steps (Step-Functions/actor style), not Temporal's
+  "write normal code, we checkpoint it invisibly." A *DX* difference, recoverable
+  later via a continuation-compiling SDK.
+- **`awaitEvent`/join is real new design** (§4.1–4.2), the main engineering risk.
+- **Single-Postgres ceiling** — honest "up to a few thousand workflow
+  transitions/sec per database" framing, as DBOS does; concede hyperscale to
+  Temporal.
+- **absurd already has distribution** in the "Postgres-only durable workflows"
+  framing. PgQue's counter is not "also Postgres" but "**zero-bloat at
+  throughput absurd's mutable-row design can't sustain**" — a concrete,
+  benchmarkable claim, not a me-too.
+
+### Success probability (revised)
+
+- A **rotation-native, event-sourced durable-execution layer** marketed on
+  *zero-bloat high-throughput durable workflows*: **moderate-to-high** — it is
+  differentiated, reduces to existing primitives, and rides existing adoption.
+- A **DBOS/absurd clone** (mutable status row + multi-language replay runtime):
+  **low** — late, undifferentiated, and it would forfeit the one advantage.
+
+The strategic point: don't enter the category the way the incumbents built it.
+Enter it the way only PgQue *can* build it.
+
+---
+
+## 6. Strategic options
+
+**Tier 0 — Stay a pure queue.** Lowest risk; forgoes a genuine, defensible
+differentiator that the engine uniquely enables.
+
+**Tier 1 — Own "transactional durable enqueue" now (low risk).** Document and
+helper-ize the exactly-once handoff (§3.2) and idempotent-step patterns. Pure
+extension of the queue identity; mostly docs + small helpers + TDD examples.
+Also the foundation the durable layer builds on.
+
+**Tier 2 — Event-sourced durable steps (recommended, medium risk).** A
+`sql/experimental/durable.sql` layer:
+- continuation-passing steps over the rotating log (no mutable status row on the
+  hot path),
+- transactional handoff (`insert_event` + `finish_batch` in one txn),
+- rotating `send_at` (PR #237) for sleep/timers,
+- a bounded current-state projection + `(workflow_id, step_seq)` idempotency
+  index,
+- the `awaitEvent`/emit registry + fan-out/join primitive (the hard part —
+  design and TDD this first),
+- exactly **one** reference SDK, explicitly experimental, gated behind the
+  `PHASES.md` promotion rule.
+Marketed on the zero-bloat-at-throughput advantage, not "also Postgres."
+
+**Tier 3 — Multi-language deterministic-replay platform (not recommended).**
+Competing with Temporal/DBOS on their terms and their costs, forfeiting the
+model's advantage.
+
+---
+
+## 7. Recommendation
+
+1. **Adopt Tier 1 now** — low-cost, on-identity, and the foundation for Tier 2.
+2. **Prototype Tier 2 as an explicit experiment**, leading with the
+   `awaitEvent`/join design (the one place the model has real new risk) and a
+   throughput+bloat benchmark vs a mutable-status-row baseline (absurd/DBOS
+   shape) — that benchmark *is* the marketing.
+3. **Do not pursue Tier 3.**
+4. **Keep the queue the headline; durable steps are a feature of the engine's
+   zero-bloat append-and-rotate design**, which is exactly why PgQue can offer
+   them where SKIP-LOCKED systems hit a wall.
+
+---
+
+## 8. Open questions for the maintainers
+
+- Is there demonstrated user pull for durable steps (especially AI-agent
+  use cases), or is this category FOMO? Tier 2 should follow real pull.
+- Reference SDK first: Python (AI-agent gravity) or TypeScript (absurd-parity)?
+- `awaitEvent` semantics: race-free emit/await caching, timeout handling, and
+  fan-in/join — design and TDD before any code.
+- Does the throughput+bloat benchmark vs a mutable-status-row baseline hold up
+  on server hardware? (If yes, it is the whole pitch.)
+- Are we comfortable shipping a state-machine programming model first, with
+  linear-code DX as a later SDK project?
+
+---
+
+## Appendix — per-system one-liners
+
+- **DBOS** — embedded library, Postgres `dbos` system schema
+  (`workflow_status`, `operation_outputs`, …), **mutable status row updated per
+  step**, SKIP-LOCKED queue dequeue, ~40k workflows/sec on one Postgres, replay
+  runtime is ~80% of the work, Conductor (ops) is the proprietary money-maker.
+- **absurd** — single `absurd.sql`, per-queue `t_/r_/c_/e_/w_/i_` tables,
+  SKIP-LOCKED claim-with-lease, task-level retry, no determinism, pg_cron
+  partition detach, thin TS/Python SDKs, Rust port (TensorZero).
+- **Temporal** — separate cluster (Frontend/History/Matching/Worker),
+  event-sourced deterministic replay, Cassandra at scale, immutable
+  `numHistoryShards`, 7 SDKs, determinism is the adoption tax.
+- **Restate** — single Rust binary, log + RocksDB, virtual objects, durable
+  promises, BSL license drew "not really open source" criticism.
+- **Rivet** — Apache-2.0 actor platform (Durable-Objects-style), Postgres /
+  RocksDB / FoundationDB, broader than workflows, no multi-actor atomic txns.
+- **Silo** — Gadget's Rust broker on SlateDB/object storage, durable *job
+  queue* (not workflow engine), single-shard-per-tenant (~4k jobs/sec cap),
+  first-class concurrency + rate limiting, self-described prototype.
+</content>
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+<style>.md-table{border-collapse:collapse;width:100%;margin:1em 0;font-size:.95em;display:block;overflow-x:auto}.md-table th,.md-table td{border:1px solid var(--border,#ccc);padding:.5em .7em;text-align:left;vertical-align:top}.md-table th{background:rgba(127,127,127,.12);font-weight:600}</style></head>
+<body>
+<div class="progress" aria-hidden="true"><i id="pb"></i></div>
+<header class="metabar">
+<div class="metabar-row">
+<div class="metabar-left">
+<span class="brand">workflows</span>
+<span class="chip">v<b>v0.5</b></span>
+<span class="chip">2026-05-30</span>
+</div>
+<div class="metabar-right">
+<span class="status">brief</span>
+<span class="theme-sw" role="group" aria-label="Theme">
+<button data-v="light" title="Light">&#9728;</button>
+<button data-v="dark" title="Dark">&#9790;</button>
+<button data-v="auto" title="System" class="active">&#9680;</button>
+</span>
+</div>
+</div>
+</header>
+<main class="brief">
+<header class="brief-hero">
+<p class="brief-kicker">Brief — derivative summary</p>
+<h1 class="brief-title">PgQue Durable Workflows — SPEC v0.5</h1>
+<p class="brief-subtitle">
+<code>workflows</code> ·
+ Version v0.5 ·
+ Published <time>2026-05-30T09:41:56.622Z</time> ·
+ <a href="./SPEC.md">canonical SPEC.md →</a>
+</p>
+<p class="brief-warning">
+Summary, not the spec. Skim this for shape, architecture, scope, risks, decisions, and open questions in 5–10 minutes; consult <a href="./SPEC.md">SPEC.md</a> for the full text.
+</p>
+</header>
+<nav class="brief-toc">
+<div class="brief-toc-title">In this brief</div>
+<ol>
+<li><a href="#s-goal"><span class="num">01</span><span>Goal</span></a></li>
+<li><a href="#s-1-goal-why-it-s-needed"><span class="num">02</span><span>1. Goal &amp; why it&#39;s needed</span></a></li>
+<li><a href="#s-2-scope-resolved-interview-decisions"><span class="num">03</span><span>2. Scope &amp; resolved interview decisions</span></a></li>
+<li><a href="#s-3-user-stories"><span class="num">04</span><span>3. User stories</span></a></li>
+<li><a href="#s-4-architecture"><span class="num">05</span><span>4. Architecture</span></a></li>
+<li><a href="#s-5-implementation-details"><span class="num">06</span><span>5. Implementation details</span></a></li>
+<li><a href="#s-6-tests-plan"><span class="num">07</span><span>6. Tests plan</span></a></li>
+<li><a href="#s-7-team-veteran-experts-to-hire"><span class="num">08</span><span>7. Team (veteran experts to hire)</span></a></li>
+<li><a href="#s-8-implementation-plan-sprints-parallelization-ordering"><span class="num">09</span><span>8. Implementation plan (sprints, parallelization, ordering)</span></a></li>
+<li><a href="#s-9-topic-specific-api-surface-reference-sdk-python-v0-1"><span class="num">10</span><span>9. Topic-specific: API surface (reference SDK, Python v0.1)</span></a></li>
+<li><a href="#s-10-operability-notes-managed-pg"><span class="num">11</span><span>10. Operability notes (managed-PG)</span></a></li>
+<li><a href="#s-11-open-items-carried-to-v0-6"><span class="num">12</span><span>11. Open items carried to v0.6</span></a></li>
+<li><a href="#s-12-non-goals-disclaimers-honored-strictly-not-reintroduced-anywhere-above"><span class="num">13</span><span>12. Non-goals / disclaimers (honored strictly — not reintroduced anywhere above)</span></a></li>
+<li><a href="#s-13-embedded-changelog"><span class="num">14</span><span>13. Embedded Changelog</span></a></li>
+</ol>
+</nav>
+<section class="brief-goal" id="s-goal">
+<h2><span class="n">01</span><span>Goal</span></h2>
+<p>&gt; Status: <strong>experimental</strong>, ships as optional <code>sql/experimental/durable.sql</code> gated by the project promotion rule. Workflow support ships first as <strong>one thin-SQL-wrapper reference client (Python)</strong>; the other PgQue clients (Go, TypeScript, + WIP) are a planned follow-up, not v0.1 (§7–§9, §12). Engine layer is sacred and untouched.</p>
+</section>
+<section class="brief-section brief-section-generic" id="s-1-goal-why-it-s-needed">
+<h2><span class="n">02</span><span>1. Goal &amp; why it&#39;s needed</span></h2>
+<p><strong>Goal (user-outcome language).</strong> Give developers durable, crash-proof workflows — multi-step processes and AI-agent loops that never lose progress and run exactly-once — using only the Postgres they already operate, with no separate system to run, and that <strong>keep running fast under sustained high volume instead of degrading over time</strong> (no gradual slowdown, no VACUUM wall, no throughput cliff, no tuning, no 3am pager).</p>
+<p><strong>Positioning.</strong> This is a <strong>lighter, no-new-infra, stays-fast alternative to Temporal and DBOS</strong> — it competes with them head-on on durable execution and delivers the same core guarantees teams adopt those systems for (durable multi-step execution, exactly-once handoff, at-least-once steps, durable timers, fan-out/join), running entirely inside your existing managed Postgres and <strong>not slowing down under load</strong>. Eliminating per-step <code>workflow_status</code> <code>UPDATE</code> churn is the <strong>headline benefit</strong>, not a limitation. We compete on durability; we differ only in <em>mechanism</em> (explained as the <em>how</em> below, never sold as the <em>what</em>). Throughput target: <strong>tens of thousands of simple (await-light) transitions/sec per database, flat under sustained load</strong> (higher with batching), with the headline being that it <strong>does not degrade</strong> where status-row systems hit the VACUUM wall; coordination-heavy (await/join) transitions cost more and are characterized honestly (§5.6). Beyond a single node, scale out by <strong>sharding workflows across databases</strong>.</p>
+<p><strong>Why this exists.</strong> Every Postgres-native durable-execution engine in the category (DBOS, absurd, and the long tail of <code>SELECT … FOR UPDATE SKIP LOCKED</code> + <code>DELETE</code> queues) shares one structural liability: they model a workflow as a <strong>mutable <code>workflow_status</code> row that is <code>UPDATE</code>d on every step</strong>. At the throughput the category is actually chasing — AI agent loops doing millions of cheap iterations — that per-step <code>UPDATE</code> churns dead tuples until the workload hits a VACUUM wall, and throughput degrades. The result users feel is a system that is fast in the demo and slow in month three. PgQ already solved exactly this for <em>queues</em> with snapshot-batch isolation + wholesale <code>TRUNCATE</code> rotation: zero dead-tuple bloat under sustained load. This product carries that property up to the workflow layer.</p>
+</section>
+<section class="brief-section brief-section-decisions" id="s-2-scope-resolved-interview-decisions">
+<h2><span class="n">03</span><span>2. Scope &amp; resolved interview decisions</span></h2>
+<p>The interview answers were all delegated to the lead (&quot;decide for me&quot;). Resolved:</p>
+<table class="md-table"><thead><tr><th>Question</th><th>Decision (v0.1, carried through)</th></tr></thead><tbody><tr><td><strong>Primary users</strong></td><td>Backend engineers running long-lived or high-iteration orchestration (AI agent loops, multi-step business processes, fan-out jobs) <strong>on managed Postgres</strong> who refuse a second datastore and refuse a VACUUM wall.</td></tr><tr><td><strong>Core job</strong></td><td>Advance a workflow from one step to the next with <strong>exactly-once handoff</strong> and <strong>at-least-once step execution</strong>, never losing or silently duplicating a workflow&#39;s progress — on a hot path that appends and rotates rather than updates.</td></tr><tr><td><strong>Durability / recovery guarantee</strong></td><td>At-least-once step execution + exactly-once handoff between steps; per-step idempotency keyed on <code>(workflow_id, step_seq)</code>. On crash, exactly the single in-flight step redelivers (PgQ&#39;s existing redelivery); there is no long function to replay.</td></tr><tr><td><strong>Success metric</strong></td><td>A throughput-and-bloat benchmark vs a mutable-status-row baseline (DBOS/absurd shape) on server hardware: <strong>flat dead-tuple count + sustained throughput</strong> on the append+rotate hot path where the baseline degrades.</td></tr><tr><td><strong>Out of scope for v0.1</strong></td><td>Cancellation / orphan-join propagation; linear-code (<code>async/await</code>-compiled) DX sugar; the per-language deterministic-replay <em>runtime</em> (we ship one thin SQL-wrapper reference client — Python — instead, §9); additional-language clients (Go/TS/WIP — a deferred follow-up, §11); imposing a determinism requirement on user code. <strong>In scope:</strong> the one Python reference client, the full durability/coordination engine, and the observability surface of §5.14.</td></tr></tbody></table>
+<p>---</p>
+</section>
+<section class="brief-section brief-section-generic" id="s-3-user-stories">
+<h2><span class="n">04</span><span>3. User stories</span></h2>
+<p>Each story is persona + action + outcome and is directly exercised as a manual acceptance test (§6.4).</p>
+<p>---</p>
+<ul>
+<li><strong>Agent-loop builder (stays fast at iteration scale).</strong> <em>As</em> a backend engineer running an AI agent that loops thousands of times per run, <em>I</em> define each iteration as a step that processes and enqueues its successor, <em>so that</em> a million iterations complete with <strong>no gradual slowdown and a flat dead-tuple count</strong> on the hot tables — verifiable with <code>pg_stat_user_tables.n_dead_tup</code> staying flat through the run. (The flat-curve claim is scoped to await-light loops; await/join-heavy shapes are characterized honestly in §5.6.)</li>
+</ul>
+</section>
+<section class="brief-section brief-section-architecture" id="s-4-architecture">
+<h2><span class="n">05</span><span>4. Architecture</span></h2>
+<p>&lt;!-- architecture:begin --&gt;</p>
+<p>&lt;!-- architecture:end --&gt;</p>
+<p>The durable layer <strong>only calls</strong> the PgQ primitives + <code>send_at</code>. It adds <strong>no</strong> modification to rotation/tick/batch logic and introduces <strong>no</strong> second concurrency model. Its dependencies on engine semantics (tick-visibility, durable per-event retry count, <code>send_at</code>, the <code>next_batch</code> max-events bound) are made explicit and pinned by engine-contract tests (§5.9).</p>
+<ul>
+<li><strong>Workflow</strong> — a logical state machine identified by <code>workflow_id</code>, which is a <strong>128-bit unguessable capability</strong> (§5.11), not a sequential id. At any instant it is in exactly one of three conditions: <strong>(a)</strong> one <em>in-flight</em> message (a step-event sitting in a PgQ batch being processed), <strong>(b)</strong> <em>scheduled</em> (a <code>send_at</code> continuation awaiting a wake time, or a registered wait awaiting an event), or <strong>(c)</strong> <em>terminal</em>. The <strong>single-live-continuation invariant</strong> — each processed step enqueues <em>exactly one</em> successor — is what makes exclusivity structural rather than lease-based.</li>
+<li><strong><code>workflow_id</code> — addressing handle AND bearer capability.</strong> It is used both to <em>address</em> a workflow (in payloads, user tables) and, combined with the role grants and per-wait tokens of §5.10, to <em>authorize</em> operations against it. Because it does double duty it must be treated as a secret; §5.11 specifies its confidentiality/leakage model (hashed at rest in audit/DLQ, never logged raw, mandatory token for approval waits).</li>
+<li><strong>Step-event</strong> — the message on the PgQ queue. Payload carries: <code>workflow_id</code>, <code>step_seq</code> (monotonic progress anchor), <code>step_name</code>/state tag, <code>delivery_anchor</code> (the event&#39;s deliverable time, §5.4.1), small continuation state (continuation-passing), and — for retries — <code>retry_attempt</code>/<code>origin_step</code> (§5.2), subject to a <strong>hard payload size cap</strong> (§5.12). <code>workflow_id</code>/<code>step_seq</code>/<code>step_name</code> are also placed in <code>ev_extra1/2/3</code> for indexed observability (§5.14.2). Large state is the user&#39;s responsibility to hold in their own tables, addressed by <code>workflow_id</code>.</li>
+<li><strong>Transition</strong> — process a step → emit successor as a <em>new append</em>. Never an <code>UPDATE</code> of a status row.</li>
+<li><strong>Coordination side tables</strong> (the only mutable state; see §5.5) — <code>wf_registry</code>, <code>wf_wait</code>, <code>wf_event_cache</code>, <code>wf_join</code>, <code>wf_join_done</code>, <code>wf_dedup</code>, <code>wf_audit</code>, the consumer-wide <code>wf_dispatch_control</code> (one row per logical consumer, §5.2), and the <strong>optional, opt-in</strong> <code>wf_live</code> projection. Their churn is bounded by <strong>concurrency and coordination-point count, not total step volume</strong> — stated precisely (distinguishing live row-count from dead-tuple rate, and conceding the await/join-heavy case) in §5.6.</li>
+</ul>
+<pre data-lang="text"><code class="language-text">(architecture not yet specified)</code></pre>
+<details class="brief-subsections">
+<summary>Subsections (3)</summary>
+<ol><li>4.1 Layering (the sacred boundary)</li>
+<li>4.2 Key abstractions</li>
+<li>4.3 Concurrency / ownership model</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-5-implementation-details">
+<h2><span class="n">06</span><span>5. Implementation details</span></h2>
+<p>The foundational guarantee. <code>insert_event()</code> (enqueue successor) and <code>finish_batch()</code> (ack) run in the <strong>consumer&#39;s own transaction</strong>. <strong>The atomic commit unit is the batch transaction</strong> (§5.2); for the common case of a single-event batch it reduces exactly to one step&#39;s side effects + its successor enqueue + its ack committing together:</p>
+<p>The dedup marker is keyed on <em>this attempt&#39;s</em> <code>(workflow_id, step_seq)</code>. A retry continuation is a <strong>new transition with a fresh <code>step_seq</code></strong> (§5.2), so it carries its own marker and is therefore <strong>not</strong> absorbed as a dedup no-op — it re-executes. <strong>No subtransactions are used on this path</strong> (hard constraint; also §5.13).</p>
+<p>The single most important objection, answered head-on. <strong>No</strong> — and the reason is the same batching amortization that makes PgQ itself cheap:</p>
+<ul>
+<li><strong>Commit</strong> ⇒ successor durably enqueued <strong>AND</strong> batch finished, atomically ⇒ exactly-once handoff.</li>
+<li><strong>Crash before commit</strong> ⇒ txn aborts ⇒ no successor, no dedup marker, batch not finished ⇒ the step redelivers cleanly.</li>
+</ul>
+<pre><code>begin;
+  -- 1. step&#39;s own DB side effects (idempotent or naturally in-txn)
+  -- 2. record per-step dedup marker (workflow_id, step_seq)   [if first delivery]
+  perform pgque.insert_event(queue, next_state);   -- enqueue exactly one successor
+  perform pgque.finish_batch(batch_id);            -- ack this batch
+commit;</code></pre>
+<pre><code>loop:
+  K        := dispatch_control.current_max_events           -- shared, consumer-wide (§5.5)
+  batch_id := pgque.next_batch(queue, consumer, max_events := K)   -- snapshot-bounded, ≤ K events
+  if batch_id is null:
+      run_timeout_sweep()                              -- §5.7.1 in-loop liveness
+      sleep to next tick; continue
+  events  := pgque.get_batch_events(batch_id)
+  begin
+    for each event in events:                          -- batch step execution
+        if redelivery_age(event) &gt; dedup_horizon:      -- §5.4.1 staleness GATE, BEFORE body
+            route_to_dlq(event); continue              --   route-not-process: no user body runs
+        advance_one(event)                             -- §5.3, appends successor(s)
+    pgque.finish_batch(batch_id)
+    run_timeout_sweep()                                -- opportunistic
+  commit
+  on abort:  note_batch_abort()                        -- ramps dispatch_control down (below)
+  on clean commit at K=1:  note_clean_isolated_commit() -- ramps dispatch_control back up</code></pre>
+<pre><code>dedup_horizon  ≥  max_retry_backoff        (one attempt&#39;s backoff)
+               +  dead_interval             (worst-case takeover delay)
+               +  max_batch_duration
+               +  safety_margin</code></pre>
+<details class="brief-subsections">
+<summary>Subsections (8)</summary>
+<ol><li>5.1 The hot path: one transition = append + ack, atomically</li>
+<li>5.1.1 The make-or-break rebuttal: &quot;isn&#39;t per-workflow state a per-transition UPDATE, 1:1 with messages → same bloat?&quot;</li>
+<li>5.2 Dispatch loop, transaction boundary, and retry</li>
+<li>5.3 The five durable-execution requirements, mapped</li>
+<li>5.4 Per-step idempotency</li>
+<li>5.5 Coordination side tables</li>
+<li>5.6 The honest zero-bloat / stays-fast claim (row-count vs dead-tuple rate, incl. the await/join-heavy case)</li>
+<li>5.6.1 Honest latency characterization (separate from bloat)</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-6-tests-plan">
+<h2><span class="n">07</span><span>6. Tests plan</span></h2>
+<p><strong>Red/green TDD for ALL new code.</strong> Every function below is written test-first: a failing test asserting the behavior, then the implementation that makes it pass. CI rejects any new SQL function or SDK method without a preceding failing-then-passing test in the same change.</p>
+<p>Each of the six user stories has a runnable scenario script the reviewer executes by hand against a managed-PG-like instance, including the §3.3 forged-approval negative check (with and without the per-wait token), the §3.2 long-sleep-resumes-not-DLQ&#39;d check, the §3.4 concurrent-completer exactly-once-resume check, and the §3.6 observability walkthrough.</p>
+<p>Throughput-and-bloat benchmark vs a mutable-status-row baseline (DBOS/absurd shape) on server hardware. Publishes, over a long sustained run: <strong><code>n_dead_tup</code></strong> (flat for the PgQue await-light hot path; rising for baseline), <strong>sustained transitions/sec</strong> (targeting tens of thousands per database for await-light, flat under sustained load, §1/§5.6.1), the <strong>coordination-table dead-tuple curve</strong>, and an explicit <strong>await/join-heavy A/B workload</strong> that coordinates on (nearly) every step, so the §5.6 scoped headline is substantiated rather than asserted. Because long VACUUM-wall runs are slow and noisy, this is a <strong>nightly / on-demand gated harness</strong>, explicitly out of the per-change CI gate (which runs only a short smoke version). The full harness is reproducible and versioned.</p>
+<ul>
+<li><strong>Exactly-once handoff</strong> (§5.1) — kill the txn between <code>insert_event</code> and <code>commit</code>, assert no successor + clean redelivery; assert no double-handoff on commit.</li>
+<li><strong>Per-step idempotency + dedup-horizon + delivery-anchor clock</strong> (§5.4/§5.4.1) — deliver the same <code>(workflow_id, step_seq)</code> twice → exactly one successor + one side effect; redeliver at horizon-boundary age → routed to DLQ, no double-handoff; <strong>the mandatory positive test: a <code>sleep</code> longer than <code>dedup_horizon</code> resumes normally and is NOT DLQ&#39;d</strong>; <strong>AND the staleness-gate ordering test: the §5.4.1 staleness check runs and commits its DLQ route BEFORE any user body executes, and a stale event is never handed to a body that aborts</strong> (guards the §5.4.1↔§5.2 reconciliation).</li>
+<li><strong>Transaction-boundary / retry resolution</strong> (§5.2) — a retry continuation re-enqueues via <code>send_at</code> with a <strong>fresh <code>step_seq</code></strong> and, on delivery, <strong>re-executes its body</strong> (assert the step logic runs once per retry attempt up to <code>max_retries</code>, then lands in DLQ); an unexpected exception aborts only a bounded batch; <strong>single-dispatcher poison-pill isolation: a poison event sharing a starting batch of size K with several innocent co-tenant workflows is quarantined to the DLQ via consumer-wide <code>max_events</code>-reduction-to-1, and every innocent co-tenant ultimately commits and is NOT DLQ&#39;d</strong>; <strong>AND the multi-subconsumer redelivery test: with ≥2 cooperative subconsumers running, an aborting poison event is redelivered to a DIFFERENT subconsumer than the one that aborted, and the consumer-wide <code>wf_dispatch_control</code> reduction ensures that other subconsumer also requests size-1 batches — assert the poison is NOT re-aggregated with innocents at <code>max_events=K</code> and no innocent co-tenant is forced to the DLQ</strong> (guards the subconsumer-safety fix; exercises engine contract #4 across subconsumers); <strong>AND the quarantine up-ramp test: after <code>quarantine_cooldown</code> clean size-1 commits, <code>current_max_events</code> is restored to K</strong>.</li>
+<li><strong><code>awaitEvent</code> / <code>emit</code> race matrix</strong> (§5.7) — one test per row; <code>cache_retention_horizon</code> never drops a within-horizon entry and is <strong>independent of <code>await_timeout</code></strong> (a long await behind a fast emit is not rejected, §5.7.2); advisory-lock serialization correct under simulated transaction-pooling, including a <strong>hash-collision correctness-safety</strong> test (§5.7.3); single-resume token proven by concurrent emit+sweep.</li>
+<li><strong>fan-out / join</strong> (§5.8) — race-free join-total recording; idempotent completed-set under duplicated completion; <strong>exactly-once parent resume proven with CONCURRENT FINAL COMPLETERS — assert the parent IS resumed exactly once (not zero, not twice), exercising the per-join completion lock at READ COMMITTED</strong>; <strong>per-child result array assembled from <code>wf_join_done</code> (spill) with a resume payload under <code>max_payload_bytes</code> at full <code>max_spawn_fanout</code></strong>; spawn-fanout cap enforced.</li>
+<li><strong>Authorization &amp; capability</strong> (§5.10/§5.11) — PUBLIC cannot execute any durable function; <code>emit</code> without the <code>workflow_id</code> capability fails; <code>emit</code> for an id absent from <code>wf_registry</code> is rejected with no cache row; an approval-class <code>emit</code> without the mandatory per-wait token fails even with a valid id; forged-approval with a guessed sequential id fails; <strong><code>workflow_id</code> column is defaulted by <code>gen_random_uuid()</code>/<code>pgcrypto</code> and CI statically rejects any sequence/serial-derived id path</strong>; <code>wf_audit</code>/DLQ store hashed ids; audit row with <code>actor_id</code> written for every emit/resume/spawn.</li>
+<li><strong>Observability surface</strong> (§5.14) — parked-workflow view returns correct waiting/sleeping/overdue sets; <code>ev_extra1</code>-indexed running-set query returns the in-flight window; <code>wf_audit</code>-derived metrics view returns correct counts; <code>wf_live</code> boundary-granularity reflects start/park/terminal with no per-step write, and high-resolution opt-in reflects exact current step (asserting the per-step <code>UPDATE</code> happens only in high-res mode).</li>
+</ul>
+<details class="brief-subsections">
+<summary>Subsections (5)</summary>
+<ol><li>6.1 Hard repo rule</li>
+<li>6.2 Built test-first, in this order (highest risk first)</li>
+<li>6.3 CI test suites</li>
+<li>6.4 Manual acceptance (maps 1:1 to §3 user stories)</li>
+<li>6.5 Success-criterion benchmark (the entire pitch) — gated, NOT a per-change CI suite</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-7-team-veteran-experts-to-hire">
+<h2><span class="n">08</span><span>7. Team (veteran experts to hire)</span></h2>
+<p>Veteran <strong>&quot;Durable Workflow Engineer&quot;</strong> (accepted).</p>
+<p>---</p>
+<ul>
+<li><strong>Veteran PostgreSQL internals / MVCC engineer (1)</strong> — snapshot/visibility reasoning, <code>xid8</code>/<code>pg_snapshot</code>, rotation interaction, no-subtransaction guarantee, engine-contract tests (§5.9 incl. the <code>next_batch</code> max-events bound and its cross-subconsumer redelivery semantics), engine-floor install gate.</li>
+<li><strong>Veteran durable-execution / distributed-systems engineer (1)</strong> — await/emit and fan-out/join race designs, single-resume-token proofs, the join-completion serialization + lost-resume closure (§5.8), the dedup-horizon + delivery-anchor bound (§5.4.1), the transaction-boundary/retry resolution incl. retry-<code>step_seq</code> semantics and the consumer-wide <code>wf_dispatch_control</code> poison-pill <code>max_events</code> size-1 isolation + up-ramp recovery (§5.2).</li>
+<li><strong>Veteran PostgreSQL security engineer (0.5, shared)</strong> — authorization model (§5.10), capability generation + confidentiality/leakage model (§5.11), mandatory per-wait token, audit attribution under pooling, grant-audit tests, resource caps (§5.12).</li>
+<li><strong>Veteran PL/pgSQL + SQL test engineer (pgTAP) (1)</strong> — red/green TDD harness, concurrency/property tests (incl. concurrent-completer join liveness AND multi-subconsumer poison-isolation), crash-recovery + pg_cron-disabled and scale-to-zero liveness injection, the positive long-sleep-not-DLQ&#39;d, staleness-gate-ordering, retry-re-execution, and quarantine up-ramp tests.</li>
+<li><strong>Veteran SDK / developer-experience engineer (Python) (1)</strong> — the one reference SDK and the thin-client surface, incl. <code>awaitAll</code> result-array assembly from the spill table; the SDK side of the observability surface.</li>
+<li><strong>Veteran observability / SRE engineer (0.5, shared)</strong> — the §5.14 views, <code>ev_extra1</code> index, <code>wf_audit</code>→OTel/Prometheus/ClickHouse export pipeline, workflows-overview + DLQ inspection.</li>
+<li><strong>Veteran performance / benchmarking engineer (1)</strong> — the gated throughput-and-bloat benchmark incl. the await/join-heavy A/B and the published curves.</li>
+<li class="brief-more">…1 more in SPEC.md</li>
+</ul>
+<details class="brief-subsections">
+<summary>Subsections (1)</summary>
+<ol><li>7.1 Persona for this spec round</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-8-implementation-plan-sprints-parallelization-ordering">
+<h2><span class="n">09</span><span>8. Implementation plan (sprints, parallelization, ordering)</span></h2>
+<p><strong>Sprint 0 — Foundations &amp; harness (1 wk).</strong></p>
+<p><strong>Sprint 1 — Exactly-once core (1.5 wk).</strong> <em>(highest risk first)</em></p>
+<p><strong>Sprint 2 — Coordination primitives (2 wk).</strong> <em>Two parallel tracks:</em></p>
+<ul>
+<li>Test engineer: pgTAP red/green harness, CI matrix (PG 14–18), engine-sacredness diff-guard, grant-audit scaffold. <em>(blocks everyone.)</em></li>
+<li>PG-internals engineer: spike the primitive reduction; confirm <code>send_at</code> (PR #237), the durable per-event retry counter, <strong>and the <code>next_batch</code> max-events bound incl. cross-subconsumer redelivery (contract #4)</strong>; draft the engine-contract tests + install-time engine-floor gate (§5.9).</li>
+<li>Security engineer: role model + <code>REVOKE</code>-from-PUBLIC install template + capability generation and leakage-hygiene defaults (§5.11).</li>
+<li><em>Parallel:</em> SDK engineer scaffolds the thin Python client against stub SQL signatures.</li>
+</ul>
+</section>
+<section class="brief-section brief-section-generic" id="s-9-topic-specific-api-surface-reference-sdk-python-v0-1">
+<h2><span class="n">10</span><span>9. Topic-specific: API surface (reference SDK, Python v0.1)</span></h2>
+<p>Every SDK call compiles to one of the PgQ primitives + a coordination-table touch, subject to the authorization (§5.10) and resource (§5.12) checks. The programming model is a message-driven <strong>state machine</strong> (think AWS Step Functions / actors). <strong>One reference client (Python) in v0.1; other-language clients (Go/TS/WIP) are a deferred follow-up</strong> (§11/§12) — cheap to add later precisely because durability lives in SQL and each client is a thin wrapper, kept aligned by a shared cross-client conformance suite. <strong>No</strong> <code>async/await</code>-compiled linear-code DX in v0.1 (deferred, §12).</p>
+<p>---</p>
+<pre data-lang="python"><code class="language-python">wf = defineWorkflow(&quot;order_fulfillment&quot;)
+
+@wf.step(&quot;charge&quot;)
+def charge(ctx, state):
+    ctx.side_effect(...)              # user&#39;s own idempotent/in-txn write
+    return ctx.goto(&quot;await_ship&quot;, state)        # append successor
+
+@wf.step(&quot;await_ship&quot;)
+def await_ship(ctx, state):
+    return ctx.await_event(&quot;shipped&quot;, timeout=&quot;24h&quot;,
+                           on_event=&quot;notify&quot;, on_timeout=&quot;escalate&quot;,
+                           require_token=True)   # mandatory token for approval-class
+
+@wf.step(&quot;fan&quot;)
+def fan(ctx, state):
+    return ctx.spawn([...N children...], join=&quot;collect&quot;)   # N ≤ max_spawn_fanout
+
+@wf.step(&quot;collect&quot;)
+def collect(ctx, state):
+    results = ctx.join_results()      # assembled from wf_join_done spill (§5.8)
+    ...
+
+# authorized external producer (role: pgque_durable_client), holding the capability + wait token:
+emit(workflow_id, &quot;shipped&quot;, payload, token=wait_token, actor_id=&quot;svc:shipping&quot;)</code></pre>
+</section>
+<section class="brief-section brief-section-generic" id="s-10-operability-notes-managed-pg">
+<h2><span class="n">11</span><span>10. Operability notes (managed-PG)</span></h2>
+<p>---</p>
+<ul>
+<li><strong>pg_cron — required for scale-to-zero (§5.7.1).</strong> For always-on-dispatcher topologies it is an optimization; for serverless / scale-to-zero, pg_cron driving <code>run_timeout_sweep()</code> is a <strong>correctness requirement</strong> for timeout liveness. The install script warns if neither a long-running dispatcher nor pg_cron is configured.</li>
+<li><strong>Engine floor (§5.9/§5.13):</strong> install gates on the minimum PgQ engine version — <code>send_at</code> present, durable per-event retry counter exposed, tick-visibility per contract, <code>next_batch</code> honoring the <code>max_events</code> bound (incl. cross-subconsumer redelivery) — and fails loudly otherwise.</li>
+<li><strong>Poison-pill quarantine is consumer-wide (§5.2).</strong> Operators should know that a persistently-aborting (poison) event transiently collapses the <em>entire logical consumer</em> to size-1 batches until the event is DLQ&#39;d and <code>quarantine_cooldown</code> clean commits restore throughput — a brief, self-healing throughput dip, not a per-process anomaly. <code>quarantine_cooldown</code> and starting <code>K</code> are documented tunables.</li>
+<li><strong>Required operator settings:</strong> documented autovacuum tuning for the <code>DELETE</code>-driven coordination tables (<code>wf_registry</code>, <code>wf_wait</code>, <code>wf_join</code>) and for <code>wf_live</code> if enabled (HOT-update churn at its configured granularity, §5.5) so their dead-tuple rate (§5.6) stays bounded; rotation cadence for <code>wf_dedup</code>/<code>wf_event_cache</code>/<code>wf_audit</code>. The await/join-heavy dead-tuple characterization (§5.6) is documented so operators size autovacuum for their workload shape.</li>
+<li><strong>Observability (§5.14):</strong> enable the optional <code>ev_extra1</code> index for the running-set view; wire the <code>wf_audit</code> export to OTel/Prometheus/ClickHouse; choose <code>wf_live</code> granularity (boundary default vs per-step opt-in) per the bloat/visibility trade.</li>
+<li><strong>Capability-leakage hygiene (§5.11):</strong> disable statement-parameter logging for the durable schema; <code>workflow_id</code> is stored hashed in <code>wf_audit</code> and DLQ; treat the id as a secret and prefer the mandatory per-wait token for approvals.</li>
+<li><strong>Audit export (§5.10.3):</strong> the <code>wf_audit</code> rotating table must be exported to durable storage before rotation; export hook + retention policy are part of the docs. Honest limitation: the log is append-only-by-convention, not cryptographically tamper-evident (hash-chaining deferred, §11).</li>
+<li class="brief-more">…1 more in SPEC.md</li>
+</ul>
+</section>
+<section class="brief-section brief-section-generic" id="s-11-open-items-carried-to-v0-6">
+<h2><span class="n">12</span><span>11. Open items carried to v0.6</span></h2>
+<p>---</p>
+<ul>
+<li>Quantitative defaults for every configured bound (<code>dedup_horizon</code>, <code>cache_retention_horizon</code>, <code>max_spawn_fanout</code>, <code>max_payload_bytes</code>, emit rate, starting batch <code>K</code>, <code>quarantine_cooldown</code>) validated against the benchmark.</li>
+<li>Per-wait emit-token issuance/rotation/revocation detail (§5.10.2) — now mandatory for approval-class, but the token lifecycle is still to be fully specified.</li>
+<li><strong>Audit hash-chaining / signing</strong> for genuine tamper-evidence (§5.10.3) — deferred enhancement beyond append-only-by-convention.</li>
+<li><strong>A verification pass on the v0.5 fix-induced redesigns before promotion</strong> — specifically: the consumer-wide <code>wf_dispatch_control</code> poison-pill isolation + up-ramp recovery across subconsumers (§5.2, new table, new multi-subconsumer test) and its interaction with engine contract #4&#39;s cross-subconsumer redelivery (§5.9); the unified <code>wf_live</code> one-row-per-live-workflow HOT-update model (§5.5); and the §5.4.1↔§5.2 staleness-gate-ordering / dual-DLQ-route reconciliation. These want independent confirmation — including whether a single shared <code>wf_dispatch_control</code> row becomes a write-contention point under many subconsumers + frequent aborts (expected rare, but unmeasured).</li>
+<li>Other-language clients (Go, TypeScript, + WIP) as thin SQL wrappers + the shared cross-client conformance suite — deferred follow-up after the Python reference client (§9/§12).</li>
+<li>Cancellation / orphan-join propagation remains deferred (§12).</li>
+</ul>
+</section>
+<section class="brief-section brief-section-scope-out" id="s-12-non-goals-disclaimers-honored-strictly-not-reintroduced-anywhere-above">
+<h2><span class="n">13</span><span>12. Non-goals / disclaimers (honored strictly — not reintroduced anywhere above)</span></h2>
+<p>---</p>
+<ul>
+<li><strong>Mechanism distinction (NOT a competitive disclaimer).</strong> PgQue Durable Workflows is a direct, better, no-new-infra, stays-fast <strong>alternative to Temporal and DBOS</strong> — it competes with them and delivers the same core durable-execution guarantees (§1). It deliberately does <strong>not</strong> reproduce their <em>durability mechanism</em>: deterministic replay of a long-lived linear function backed by a <code>workflow_status</code> row mutated on every step. That mechanism is precisely the source of the per-step <code>UPDATE</code> bloat we exist to eliminate. <strong>Eliminating per-step <code>UPDATE</code> churn is a goal/benefit (§1), never a non-goal.</strong> What we disclaim is only the <em>technique</em>: no determinism requirement imposed on user code, and no replay-of-a-linear-function programming model in v0.1 (a continuation-compiling SDK is deferred).</li>
+<li><strong>NOT</strong> a per-language deterministic-replay <em>runtime</em> like Temporal&#39;s heavy per-language engines. Workflow support is intended to ship across all PgQue clients eventually as <strong>thin SQL wrappers</strong> (the architecture makes that cheap), but <strong>v0.1 ships one reference client — Python</strong>; Go/TypeScript/WIP are a deferred follow-up (§9/§11), not part of the v0.1 scope or team.</li>
+<li><strong>NOT</strong> a separate server, daemon, or external datastore. No Cassandra, RocksDB, FoundationDB, or Redis.</li>
+<li><strong>Throughput is NOT conceded to a low ceiling.</strong> Target: <strong>tens of thousands of simple (await-light) transitions/sec per database, flat under sustained load</strong> (higher with batching); coordination-heavy transitions cost more and are characterized honestly (§5.6); scale beyond a single node by sharding workflows across databases — that is scale-out, not an apology. The single-workflow sequential rate is ~tick-rate and is stated plainly (§5.6.1) so the aggregate claim is not misread.</li>
+<li><strong>NOT</strong> changing the sacred PgQ engine, and <strong>NOT</strong> introducing a second <code>SELECT … FOR UPDATE SKIP LOCKED</code> claim/lease concurrency model as the primary mechanism — exclusivity comes from the single-live-continuation invariant over the existing rotation engine. (The transaction-scoped advisory lock of §5.7.3, the per-join <code>SELECT … FOR UPDATE</code>/advisory lock of §5.8, and the single per-consumer <code>wf_dispatch_control</code> row of §5.2 are coordination-table serialization/control primitives, <strong>not</strong> a workflow-claim/lease mechanism.)</li>
+<li><strong>Cancellation / orphan-join propagation is deferred</strong> to a follow-up, not in v0.1.</li>
+<li>Linear-code (<code>async/await</code>-compiled) DX is an explicit <strong>later</strong> SDK project, not an engine requirement.</li>
+</ul>
+</section>
+<section class="brief-section brief-section-generic" id="s-13-embedded-changelog">
+<h2><span class="n">14</span><span>13. Embedded Changelog</span></h2>
+<ul>
+<li><strong>v0.5</strong> (2026-05-30) — Closed the two blocking findings + three minors Reviewer B raised against v0.4 (Reviewer A unavailable this round), and re-aligned the user-facing framing to the idea&#39;s hard rules. <strong>GENUINELY populated the §4 canonical architecture block</strong> with the layered SDK→durable-layer→sacred-engine diagram inside the <code>architecture:begin/end</code> markers — correcting a twice-repeated regression where the v0.3 and v0.4 changelogs each falsely claimed the block was filled while the literal &quot;(architecture not yet specified)&quot; placeholder remained; this entry&#39;s claim is verifiable against §4 as written (the prior false v0.4 claim is corrected in the v0.4 entry below). <strong>Made the poison-pill isolation subconsumer-safe</strong>: the v0.4 <code>max_events</code>-reduction-to-1 was process-local dispatcher state, so under the mandated cooperative <em>subconsumers</em> (§4.3) a redelivered poison event could be re-aggregated with innocents by a subconsumer still at <code>max_events=K</code>; v0.5 moves the bound into a new <strong>consumer-wide <code>wf_dispatch_control</code> row</strong> (one row per logical consumer, written in a separate committed txn that survives the abort, read by every subconsumer before each <code>next_batch</code>) so the reduction is uniform across all subconsumers, and added a <strong>multi-subconsumer redelivery test</strong> (§6.2 item 3, §6.3) plus the cross-subconsumer redelivery clause to engine contract #4 (§5.9). <strong>Specified the <code>max_events</code> up-ramp/recovery policy</strong> (§5.2): restore to <code>K</code> after <code>quarantine_cooldown</code> consecutive clean size-1 commits (count-gated, not time-gated). <strong>Unified the <code>wf_live</code> model</strong> (§4.2/§5.5/§5.6): withdrew the inconsistent &quot;append-based, rotating, not insert+delete&quot; description and pinned it as a <strong>one-row-per-live-workflow HOT-<code>UPDATE</code>d projection</strong>. <strong>Reconciled the two DLQ-routing mechanisms and pinned ordering</strong> (§5.4.1/§5.2): the staleness gate is a pre-body, route-not-process check that commits cleanly before any user body runs; the engine retry counter (contract #2) is the abort-channel route after a body has run and aborted. <strong>Re-led with user outcomes</strong> per the idea&#39;s hard framing rule: §1 Goal/positioning rewritten in stays-fast/no-new-infra/crash-proof outcome language with the event-sourcing mechanism demoted to a &quot;How it works&quot; subsection; <strong>restored the idea&#39;s ambitious throughput target</strong> (tens of thousands of await-light transitions/sec per database, scale-out by sharding) and <strong>removed the &quot;a few thousand / conceded to Temporal&quot; framing</strong> the idea explicitly forbids; <strong>added the make-or-break per-transition-UPDATE rebuttal as a dedicated subsection</strong> (§5.1.1); <strong>added the honest single-workflow latency characterization</strong> (§5.6.1); <strong>added the mandated Observability section</strong> (§5.14) with a sixth on-call user story (§3.6), observability tests (§6.2 item 7), and an observability/SRE half-hire (§7). Updated team/plan/tests/open-items/ops accordingly. All five Reviewer B findings accepted.</li>
+<li><strong>v0.4</strong> (2026-05-30) — Closed all seven findings Reviewer B raised against v0.3 (Reviewer A unavailable this round). <strong>NOTE (corrected in v0.5): this entry originally claimed the §4 architecture diagram was &quot;actually populated&quot; — that claim was false; the literal &quot;(architecture not yet specified)&quot; placeholder in fact remained, repeating the identical false claim the v0.3 entry made. The block was genuinely filled only in v0.5.</strong> Corrected throughput positioning to the (later-reverted) &quot;a few thousand transitions/sec&quot; framing; <strong>v0.5 reverts this back to the idea&#39;s ambitious target.</strong> Redesigned poison-pill containment to use <strong>only the existing <code>next_batch</code> <code>max_events</code> bound (reduce to size 1)</strong> for isolation, withdrawing the v0.3 &quot;re-process the same snapshot range with the batch split&quot; framing; added the <code>next_batch</code> max-events bound as <strong>explicit engine contract #4</strong> (§5.9). <strong>(Defect found in v0.5 review: the v0.4 reduction was process-local and not subconsumer-safe — fixed in v0.5 via <code>wf_dispatch_control</code>.)</strong> Closed the fan-out/join <strong>lost-resume race</strong>: completion counting now serializes on the <code>wf_join</code> row (<code>SELECT … FOR UPDATE</code> / per-join advisory lock) at <strong>READ COMMITTED</strong>, and added a concurrent-final-completer liveness test (§5.8/§6.2/§6.3). Removed the undefined &quot;within-horizon pre-registration&quot; emit-authz clause as redundant. Reduced the client-scope claim to the <strong>one Python reference client</strong> actually staffed. Updated team, plan, tests, open items accordingly. All seven Reviewer B findings accepted.</li>
+<li><strong>v0.3</strong> (2026-05-30) — Closed the fix-induced contradictions both reviewers raised against v0.2. Redefined dedup-horizon enforcement around a per-transition <code>delivery_anchor</code> so long <code>send_at</code> sleeps are never misclassified as stale redeliveries and DLQ&#39;d, and recomputed the bound as single-attempt (§5.4.1). Pinned retry continuations to a fresh <code>step_seq</code> so they re-execute instead of being swallowed as a dedup no-op (§5.2/§5.4). Redesigned poison-pill containment onto the engine&#39;s durable per-event retry counter (§5.2), pinned as an explicit engine contract (§5.9). Replaced the unbounded per-key lock row with a transaction-scoped advisory lock (§5.7.3). Separated <code>cache_retention_horizon</code> from <code>await_timeout</code> (§5.7.2). Spilled per-child join results to <code>wf_join_done</code> (§5.8). Made timeout liveness an explicit operator invariant — pg_cron REQUIRED for scale-to-zero (§5.7.1, §10). Introduced a mandatory <code>wf_registry</code> as the authoritative emit-liveness source (§5.5/§5.10.2/§5.12). Added a <code>workflow_id</code> confidentiality/leakage model (§5.11). Corrected the audit overclaim and added <code>actor_id</code> attribution (§5.10.3). Scoped the flat-dead-tuple headline to await-light loops (§5.6/§6.5). Stated a minimum PgQ engine floor (§5.9/§5.13). Attempted to fill the empty §4 architecture block (placeholder in fact remained — corrected in v0.5). All findings from both reviewers accepted.</li>
+<li><strong>v0.2</strong> (2026-05-30) — Hardening round against Reviewer A (security/ops). Added authorization model (§5.10) and <code>workflow_id</code>-as-unforgeable-capability (§5.11). Stated the dedup-horizon bound and its DLQ enforcement (§5.4.1). Resolved the batch-transaction vs per-event-retry contradiction (§5.2). Made timeout liveness a non-optional property of the dispatch loop (§5.7.1). Pinned the await/emit lock to a pooler-safe transaction-scoped lock (§5.7.3). Bounded <code>wf_event_cache</code> retention (§5.7.2). Demoted <code>wf_live</code> to optional/opt-in (§5.5). Refined the zero-bloat claim (§5.6). Added resource caps (§5.12). Stated the engine tick-visibility coupling as a regression-tested contract (§5.9). Scoped the benchmark out of per-change CI (§6.5). Added security engineer, operability section (§10), open-items (§11). Reviewer B unavailable this round.</li>
+<li><strong>v0.1</strong> (2026-05-30) — Initial spec scaffold fleshed into full structure. Resolved all five delegated interview questions. Added Goal-&amp;-why framing, user stories, layered architecture with the sacred-engine boundary, hot-path/coordination detail incl. the honest zero-bloat correction, await/emit + fan-out/join race designs, red/green TDD-first ordering, team roster, 5-sprint plan, SDK surface, and strict non-goals. No reviewer findings yet (first authoring round).</li>
+</ul>
+</section>
+<footer class="brief-provenance">
+<p>
+Generated by <code>samospec brief workflows</code> on <time>2026-05-30T12:29:57.425Z</time>.
+ 5 review rounds —
+ lead —,
+ reviewers — +
+ —.
+</p>
+<p>Re-run after each <code>samospec publish</code> to refresh. Canonical document: <a href="./SPEC.md">SPEC.md</a>.</p>
+</footer>
+</main>
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diff --git a/blueprints/workflows/IMPLEMENTATION_RESEARCH.md b/blueprints/workflows/IMPLEMENTATION_RESEARCH.md
new file mode 100644
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+++ b/blueprints/workflows/IMPLEMENTATION_RESEARCH.md
@@ -0,0 +1,286 @@
+# Implementing Durable Workflows on PgQue — Implementation Research
+
+- **Status:** research / grounding (input to `sql/experimental/durable.sql`, not yet code)
+- **Date:** 2026-05-30
+- **Companion:** `blueprints/workflows/SPEC.md` (the conceptual spec, v0.5) and
+  `blueprints/DURABLE_EXECUTION_FEASIBILITY.md` (why this route). This document
+  grounds the spec's design in **pgque's actual primitives, tables, and verified
+  transaction semantics** — read straight from `sql/pgque.sql` (7,044 lines).
+- **Method:** every claim below is checked against the real `sql/pgque.sql`
+  function bodies and table DDL (line numbers cited), not against the conceptual
+  spec.
+
+---
+
+## 1. The keystone, verified against real code
+
+The whole design rests on one assumption: **a step's side effects, the enqueue
+of its successor, and the batch ack all commit in one transaction** (exactly-once
+handoff). Verified:
+
+- `pgque.insert_event(queue, type, data[, ev_extra1..4])` (`sql/pgque.sql:1654,
+  1678`) is plain `plpgsql` — it calls `insert_event_raw`, no internal `COMMIT`.
+- `pgque.finish_batch(batch_id)` (`:2478`) is literally **one statement**:
+  `update pgque.subscription set sub_active=now(), sub_last_tick=sub_next_tick,
+  sub_next_tick=null, sub_batch=null where sub_batch=x_batch_id`. No commit, no
+  autonomous work.
+- The only `COMMIT`s in the file are in the `ticker_loop` **procedure** (`:4142`)
+  and `upgrade_schema`; the only `pg_notify` is in the **ticker** (`:688,793,
+  5190`) — neither is on the consume/ack path.
+
+So this composes atomically and is the exactly-once-handoff primitive, for free:
+
+```sql
+begin;
+  -- 1. the step's own business writes (caller's tables)
+  -- 2. dedup marker insert (workflow_id, step_seq)         [first delivery only]
+  perform pgque.insert_event(q, step_name, payload,
+                             workflow_id, (step_seq+1)::text, null, null);
+  perform pgque.finish_batch(batch_id);
+commit;
+```
+
+Crash before `commit` ⇒ nothing happened, the step redelivers (PgQ at-least-once)
+⇒ retry. Commit ⇒ successor durably enqueued **and** batch finished. No
+subtransactions on this path (hard rule, satisfied).
+
+### 1.1 This also proves the amortization answer
+
+`finish_batch` updates **one `subscription` row per batch**, not per event — and a
+batch carries the step-events of *many* workflows. So advancing N workflows
+through a batch is **N appends (`insert_event`) + 1 subscription UPDATE**. The
+per-workflow state never becomes a per-transition row UPDATE. This is the exact
+mechanism behind the "per-batch amortization is preserved" claim.
+
+---
+
+## 2. The pgque primitives we build on (real signatures)
+
+| Primitive | Signature (`sql/pgque.sql`) | Role in the workflow layer |
+|---|---|---|
+| `insert_event` | `(queue, type, data, ev_extra1..4)` `:1678` | append a step-event / successor; `ev_extra1=workflow_id`, `ev_extra2=step_seq` |
+| `register_consumer` / `subscribe` | `:1753` | the workflow dispatcher's logical consumer |
+| `register_subconsumer` / `receive_coop` | `:5979,:6126` | parallel workers under one logical consumer; structural per-workflow exclusivity + `dead_interval` takeover |
+| `next_batch` / `get_batch_events` | `:2011,:2178` | snapshot-bounded batch of step-events to advance |
+| `finish_batch` (`ack`) | `:2478,:5385` | exactly-once handoff partner (1 row/batch) |
+| `event_retry` (`nack`) | `:2347` → `retry_queue` | transient step retry (see §5 — bloat caveat) |
+| `event_dead` / DLQ | `:4912,:4967..` | poisoned step after max retries (reuse as-is) |
+| `send_at` (experimental, PR #237) | `sql/experimental/delayed.sql` | `sleep()` and `awaitEvent` timeout — **rotating, zero-bloat** |
+| `jsontriga` | `:2917` | CDC-triggered workflow starts |
+
+### 2.1 Tables that already exist (and how they behave)
+
+- `event_template` (`:204`) — the rotating event row; **has `ev_extra1..4`**.
+  Rotated/TRUNCATEd ⇒ **zero bloat**. This is where step-events live.
+- `subscription` (`:169`) — consumer cursor; `finish_batch` UPDATEs it **per
+  batch** (HOT-updatable; one row per logical consumer/subconsumer).
+- `retry_queue` (`:231`) — `like event_template` + `ev_retry_after`, indexed on
+  `ev_retry_after`. **INSERT on `event_retry`, DELETE on `maint_retry_events`** ⇒
+  DELETE-based ⇒ **does accumulate dead tuples**. Constraint, see §5.
+- `tick`, `queue`, `consumer`, `dead_letter`, `config` — unchanged.
+
+---
+
+## 3. Workflow conventions on the event row (no new event table)
+
+A workflow step-event is an ordinary pgque event with a convention:
+
+- `ev_extra1 = workflow_id` (uuid/text) — **add a btree index on `ev_extra1`** on
+  the event tables so "find the in-flight event(s) for workflow X" and "list
+  running workflows" are indexed lookups. The index rotates/TRUNCATEs with the
+  tables ⇒ **zero bloat**, bounded to the in-flight window.
+- `ev_extra2 = step_seq` (monotonic per workflow) — progress anchor + dedup key.
+- `ev_extra3 = run/parent ids` (fan-out), `ev_extra4 = flags` (e.g. retry_attempt).
+- `ev_type = step_name`; `ev_data = continuation state` (small) or a pointer to
+  the caller's own large-state table keyed by `workflow_id`.
+
+Indexing `ev_extra1` adds one index-maintenance cost on the hot insert path
+(modest, optional, and it rotates). This is the single change to how events are
+written; everything else is convention in the payload.
+
+---
+
+## 4. Primitive-by-primitive mapping
+
+| Workflow op | Implementation on pgque |
+|---|---|
+| **start / spawn(wf, input)** | `insert_event(q, first_step, input, workflow_id, '0', …)`; insert `wf_live` row (start boundary, §6). Returns `workflow_id`. |
+| **step transition** | process event → `begin; <effects>; insert_event(successor, …, step_seq+1); finish_batch(batch); commit;` (§1). |
+| **sleep(Δ)** | `send_at(q, continuation, now()+Δ)` then `finish_batch` — **rotating delayed delivery, not `event_retry`** (§5). Step holds no open batch across the sleep. |
+| **step retry (transient)** | re-enqueue a continuation of the *same logical step* with a **fresh `step_seq`** via `send_at(now()+backoff)`; after `max_retries` → DLQ transition. (Using PgQ's `event_retry` is the built-in alternative but reuses `ev_id`/bumps `ev_retry` and is DELETE-based — see §5.) |
+| **awaitEvent(name, timeout)** | register `wf_wait(workflow_id, name, …)`; `send_at` a timeout-continuation; `finish_batch`. Resume = single-resume token (§7). |
+| **emit(workflow_id, name, payload)** | under a per-key lock: if a `wf_wait` row exists, delete it (token) + `insert_event` the resume continuation; else first-write-wins into `wf_event_cache` (§7). |
+| **spawn N children + awaitAll** | `insert_event` N child-start events (distinct child `workflow_id`) + create `wf_join(parent, total=N)` **in one txn** (tick-visibility makes total-before-children race-free); children report via idempotent `wf_join_done(parent, child_idx)`; last one resumes parent (§8). |
+| **complete / fail (terminal)** | `finish_batch` + delete `wf_live` row + append `wf_audit`. Fail after retries → `event_dead`/DLQ (existing). |
+| **dispatch / scale** | one logical consumer + cooperative subconsumers (`register_subconsumer` + `receive_coop`); `dead_interval` takeover for worker crash. Scale-out beyond one DB = independent hash-shard on `workflow_id` (separate PgQue installs), **not** pgq_node cascading. |
+
+---
+
+## 5. The retry/sleep bloat constraint (grounded finding)
+
+`event_retry` (`:2347`) INSERTs into `retry_queue`, and `maint_retry_events`
+(`:826`) later DELETEs as it moves events back — **DELETE-based, so `retry_queue`
+accumulates dead tuples** proportional to retry/sleep volume. For a workflow
+engine where `sleep` and long waits are common, leaning on `retry_queue` would
+reintroduce exactly the bloat we exist to avoid.
+
+**Resolution:** route `sleep()` and `awaitEvent` timeouts through the **rotating
+`send_at`** (PR #237: TRUNCATE-rotation, no DELETE, no VACUUM dependence), not
+`retry_queue`. Reserve `event_retry`/`retry_queue` for *transient step retries*
+only (lower volume, short backoff) — or model even those as fresh-`step_seq`
+`send_at` continuations to keep the whole hot path append+rotate. **Dependency:
+`send_at` must be promoted from `sql/experimental/` to a supported primitive
+(and land PR #237's rotation) before the durable layer can claim zero-bloat
+sleeps.**
+
+---
+
+## 6. New schema the durable layer adds (`sql/experimental/durable.sql`)
+
+All small, coordination-only; row-count bounded by **concurrency / coordination
+points**, never by total step volume (§9 bloat audit).
+
+```sql
+-- one row per LIVE workflow; observability + addressing; OPT-IN, default off.
+-- updated at park/start/terminal boundaries (NOT per step); deleted on terminal.
+create table pgque.wf_live (
+  workflow_id text primary key, queue text, state text,        -- running|waiting|sleeping
+  step_seq int, step_name text, updated_at timestamptz default now());
+
+-- registered event waits; the single-resume token (deleted on resume/timeout).
+create table pgque.wf_wait (
+  workflow_id text, event_name text, step_seq int,
+  resume_step text, timeout_at timestamptz,
+  primary key (workflow_id, event_name));
+
+-- emit-before-await cache, first-write-wins, correlation-scoped, TTL-swept.
+create table pgque.wf_event_cache (
+  event_name text primary key, payload jsonb, emitted_at timestamptz default now());
+
+-- fan-out join state + idempotent completed-set.
+create table pgque.wf_join (
+  parent_id text primary key, total int, resume_step text);
+create table pgque.wf_join_done (
+  parent_id text, child_idx int, result jsonb, ok bool,
+  primary key (parent_id, child_idx));
+
+-- per-attempt idempotency markers; APPEND-only, short-horizon, rotating.
+create table pgque.wf_dedup (
+  workflow_id text, step_seq int, created_at timestamptz default now(),
+  primary key (workflow_id, step_seq));
+
+-- append-only security/audit + history feed (exported before rotation).
+create table pgque.wf_audit (
+  ts timestamptz default now(), workflow_id text, action text, detail jsonb);
+```
+
+`wf_dedup` and `wf_event_cache` need a rotation/TTL story (mirror PR #237) so they
+don't become DELETE-bloat; `wf_live`/`wf_wait`/`wf_join` are delete-on-resolution
+(row-count bounded by concurrency).
+
+---
+
+## 7. `awaitEvent` / `emit` — concrete race handling
+
+The hard part. Build and TDD this first (two-session tests, like the repo's
+`tests/two_session_*.sh`).
+
+- **Serialize await-register vs emit-deliver** on a transaction-scoped advisory
+  lock keyed by `hashtext(workflow_id||':'||event_name)` — no lock *table*, zero
+  tuples. (PgQ already serializes batch allocation on a row lock, so this is
+  idiomatic.)
+- **emit:** `pg_advisory_xact_lock(key)`; if `wf_wait` row exists →
+  `delete … returning` (the token) + `insert_event` the resume continuation in
+  the same txn; else `insert into wf_event_cache … on conflict do nothing`
+  (first-write-wins).
+- **awaitEvent:** `pg_advisory_xact_lock(key)`; check `wf_event_cache` (resume
+  immediately if present, consume it); else insert `wf_wait` + `send_at` timeout
+  continuation; `finish_batch`.
+- **double-resume (emit racing timeout):** both resolve via
+  `delete from wf_wait where workflow_id=… and event_name=… returning *` — whoever
+  deletes first resumes; the loser gets zero rows and no-ops.
+- **redelivery of the await step:** idempotent on `(workflow_id, step_seq)` via
+  `wf_dedup`; a redelivered await whose wait was already consumed sees the
+  workflow advanced and just re-acks.
+- **cross-talk:** event names are correlation-scoped (include `workflow_id` or a
+  nonce); `wf_event_cache` TTL-swept by `maint`.
+
+---
+
+## 8. Fan-out / join — concrete
+
+- **Spawn:** in one txn, `insert_event` each child-start (distinct child
+  `workflow_id`, `ev_extra3=parent_id|child_idx`) **and** `insert wf_join(parent,
+  total=N)`. Tick visibility guarantees children aren't processed until after the
+  join row commits ⇒ "total before any child completes" is race-free for free.
+- **Child completion:** `insert into wf_join_done(parent, child_idx, result, ok)
+  on conflict do nothing` (idempotent under redelivery); then
+  `select count(*) from wf_join_done where parent_id=…`; if `= total`,
+  `delete from wf_join … returning` (token) + `insert_event` the parent resume
+  carrying the result array; all in the child's handoff txn.
+- **Partial failure:** `ok=false` rows still count toward `total`; the parent
+  resume gets a per-child result array and decides. **Cancellation / orphan-join
+  deferred** (spec non-goal).
+
+---
+
+## 9. Bloat audit, grounded in the real mechanics
+
+| Structure | Write pattern | Bloat |
+|---|---|---|
+| event tables (`event_template`-derived) | INSERT, TRUNCATE-rotate | **none** (rotation) |
+| `ev_extra1` index | rides the event tables | **none** (rotates with table) |
+| `subscription` (`finish_batch`) | 1 UPDATE per **batch** | negligible (HOT, per-consumer) |
+| `wf_dedup`, `wf_event_cache` | INSERT, rotate/TTL | none if rotated (PR #237 pattern) |
+| `wf_live`, `wf_wait`, `wf_join` | INSERT + DELETE on resolution | concurrency-bounded (live count), VACUUM-able |
+| `retry_queue` (if used for sleeps) | INSERT + DELETE | **bloats** ⇒ use `send_at` instead (§5) |
+
+Net: the **hot per-step path is append + rotate (zero bloat)**; coordination is
+concurrency-bounded; the only landmine is `retry_queue`, avoided by routing
+sleeps through rotating `send_at`.
+
+---
+
+## 10. Gaps — what pgque must add before/with the durable layer
+
+1. **Promote `send_at` to a supported primitive with PR #237 rotation.** Hard
+   dependency for zero-bloat sleeps and await-timeouts.
+2. **Optional `ev_extra1` index** (per-queue opt-in) for workflow lookup.
+3. **`sql/experimental/durable.sql`**: the tables in §6 + the functions
+   (`wf_start/step/sleep/await_event/emit/spawn/await_all/complete`), all
+   `SECURITY DEFINER … set search_path=pgque,pg_catalog`, no subtransactions.
+4. **Maint hooks**: TTL/rotation sweeps for `wf_dedup`/`wf_event_cache`, timeout
+   firing for `wf_wait` (via the existing `pgque.maint()` cadence / pg_cron).
+5. **Thin clients** in all PgQue languages (Python, Go, TS, +WIP): a worker loop
+   (`receive_coop` → dispatch by `ev_type` → handler → handoff) + the `ctx`
+   surface. Durability is in SQL, so each client stays thin.
+
+---
+
+## 11. Build order (red/green TDD, highest risk first)
+
+1. **Harness + engine-contract tests**: pin the §1 semantics (insert_event +
+   finish_batch atomic; finish_batch = 1 subscription UPDATE/batch; tick
+   visibility ordering) so the design can't silently regress on a pgque change.
+2. **Exactly-once handoff + `(workflow_id, step_seq)` dedup** (§1, §6).
+3. **`send_at`-based sleep** (depends on PR #237) + **`awaitEvent`/`emit` race
+   matrix** (§7) — two-session race tests.
+4. **fan-out / join** (§8).
+5. **Dispatch loop on cooperative consumers** + `dead_interval` takeover.
+6. **Observability** (`ev_extra1` index, `wf_live` opt-in, `wf_audit` export).
+7. **One reference client**, then the rest.
+
+---
+
+## 12. Open questions
+
+- Promote `send_at` now (its own PR) so the durable layer has a stable dep?
+- `step_seq` as `ev_extra2 text` vs a real int column — indexing/typing choice.
+- Retry policy: fresh-`step_seq` `send_at` continuations (pure append) vs PgQ's
+  `event_retry` (built-in, but DELETE-based) — recommend the former for the hot
+  path, the latter only for low-volume cases.
+- `wf_event_cache`/`wf_dedup` rotation: reuse PR #237's two-table TRUNCATE scheme
+  vs a simpler TTL `DELETE` (acceptable if volume is low).
+- Single-DB throughput target validated by the §11.1 benchmark before publishing
+  numbers.
+</content>
diff --git a/blueprints/workflows/README.md b/blueprints/workflows/README.md
new file mode 100644
index 00000000..1c973a74
--- /dev/null
+++ b/blueprints/workflows/README.md
@@ -0,0 +1,18 @@
+# PgQue Durable Workflows — spec (experimental, samospec-authored)
+
+This directory holds the versioned specification for the proposed
+**event-sourced durable-execution layer** on PgQue (see
+`../DURABLE_EXECUTION_FEASIBILITY.md` for the strategy this spec realizes).
+
+- `SPEC.md` — the spec (current version in its header).
+- `BRIEF.html` / `index.html` — self-contained HTML brief (derivative of
+  SPEC.md). `index.html` is the GitHub Pages entry point.
+- `TLDR.md`, `decisions.md`, `changelog.md`, `architecture.json` — auxiliary
+  artifacts.
+
+Authored and iterated with [samospec](https://github.com/NikolayS/samospec)
+running an all-Claude review panel (lead + two reviewer personas). Each
+version is committed and the brief republished.
+
+Status: **experimental** — ships as optional `sql/experimental/durable.sql`
+gated by the project promotion rule.
diff --git a/blueprints/workflows/SPEC.md b/blueprints/workflows/SPEC.md
new file mode 100644
index 00000000..e25367e3
--- /dev/null
+++ b/blueprints/workflows/SPEC.md
@@ -0,0 +1,501 @@
+# PgQue Durable Workflows — SPEC v0.5
+
+> Status: **experimental**, ships as optional `sql/experimental/durable.sql` gated by the project promotion rule. Workflow support ships first as **one thin-SQL-wrapper reference client (Python)**; the other PgQue clients (Go, TypeScript, + WIP) are a planned follow-up, not v0.1 (§7–§9, §12). Engine layer is sacred and untouched.
+
+---
+
+## 1. Goal & why it's needed
+
+**Goal (user-outcome language).** Give developers durable, crash-proof workflows — multi-step processes and AI-agent loops that never lose progress and run exactly-once — using only the Postgres they already operate, with no separate system to run, and that **keep running fast under sustained high volume instead of degrading over time** (no gradual slowdown, no VACUUM wall, no throughput cliff, no tuning, no 3am pager).
+
+**Positioning.** This is a **lighter, no-new-infra, stays-fast alternative to Temporal and DBOS** — it competes with them head-on on durable execution and delivers the same core guarantees teams adopt those systems for (durable multi-step execution, exactly-once handoff, at-least-once steps, durable timers, fan-out/join), running entirely inside your existing managed Postgres and **not slowing down under load**. Eliminating per-step `workflow_status` `UPDATE` churn is the **headline benefit**, not a limitation. We compete on durability; we differ only in *mechanism* (explained as the *how* below, never sold as the *what*). Throughput target: **tens of thousands of simple (await-light) transitions/sec per database, flat under sustained load** (higher with batching), with the headline being that it **does not degrade** where status-row systems hit the VACUUM wall; coordination-heavy (await/join) transitions cost more and are characterized honestly (§5.6). Beyond a single node, scale out by **sharding workflows across databases**.
+
+**Why this exists.** Every Postgres-native durable-execution engine in the category (DBOS, absurd, and the long tail of `SELECT … FOR UPDATE SKIP LOCKED` + `DELETE` queues) shares one structural liability: they model a workflow as a **mutable `workflow_status` row that is `UPDATE`d on every step**. At the throughput the category is actually chasing — AI agent loops doing millions of cheap iterations — that per-step `UPDATE` churns dead tuples until the workload hits a VACUUM wall, and throughput degrades. The result users feel is a system that is fast in the demo and slow in month three. PgQ already solved exactly this for *queues* with snapshot-batch isolation + wholesale `TRUNCATE` rotation: zero dead-tuple bloat under sustained load. This product carries that property up to the workflow layer.
+
+This exists because no one else can credibly offer "durable workflows that stay fast for months under agent-loop load, on just your managed Postgres, with no separate datastore." That is the entire pitch.
+
+**How it works / why it's possible (the mechanism — this is the *how*, not the headline).** Durable execution is event sourcing (this is how Temporal's event-history + replay works). PgQ is already an append-only event log. So instead of a mutable `workflow_status` row `UPDATE`d every step, we model each workflow as an **append-only stream of state-transition events over PgQ's snapshot + TRUNCATE rotation engine**: process a step, then **enqueue the next state as a new message** (continuation-passing) rather than mutating a row. A workflow is always either (a) one in-flight message, (b) a *scheduled* message awaiting a wake time/event, or (c) terminal; it never holds a batch open across a wait, so it never blocks rotation, and every transition is an **append**, not an `UPDATE`. That is precisely why the "stays fast under sustained load" outcome above is achievable.
+
+**What it is NOT** (honored strictly throughout — see §12): it does **not** reproduce the Temporal/DBOS *durability mechanism* (deterministic replay of a linear function + a per-step-mutated status row) — we compete with them but eliminate that mechanism because it is the bloat source; not a per-language replay *runtime* (clients are thin SQL wrappers; **one reference client — Python — in v0.1, the rest a deferred follow-up**); not a separate server/daemon/datastore; not a `FOR UPDATE SKIP LOCKED` claim/lease model; cancellation/orphan-join propagation is deferred.
+
+---
+
+## 2. Scope & resolved interview decisions
+
+The interview answers were all delegated to the lead ("decide for me"). Resolved:
+
+| Question | Decision (v0.1, carried through) |
+|---|---|
+| **Primary users** | Backend engineers running long-lived or high-iteration orchestration (AI agent loops, multi-step business processes, fan-out jobs) **on managed Postgres** who refuse a second datastore and refuse a VACUUM wall. |
+| **Core job** | Advance a workflow from one step to the next with **exactly-once handoff** and **at-least-once step execution**, never losing or silently duplicating a workflow's progress — on a hot path that appends and rotates rather than updates. |
+| **Durability / recovery guarantee** | At-least-once step execution + exactly-once handoff between steps; per-step idempotency keyed on `(workflow_id, step_seq)`. On crash, exactly the single in-flight step redelivers (PgQ's existing redelivery); there is no long function to replay. |
+| **Success metric** | A throughput-and-bloat benchmark vs a mutable-status-row baseline (DBOS/absurd shape) on server hardware: **flat dead-tuple count + sustained throughput** on the append+rotate hot path where the baseline degrades. |
+| **Out of scope for v0.1** | Cancellation / orphan-join propagation; linear-code (`async/await`-compiled) DX sugar; the per-language deterministic-replay *runtime* (we ship one thin SQL-wrapper reference client — Python — instead, §9); additional-language clients (Go/TS/WIP — a deferred follow-up, §11); imposing a determinism requirement on user code. **In scope:** the one Python reference client, the full durability/coordination engine, and the observability surface of §5.14. |
+
+---
+
+## 3. User stories
+
+Each story is persona + action + outcome and is directly exercised as a manual acceptance test (§6.4).
+
+1. **Agent-loop builder (stays fast at iteration scale).** *As* a backend engineer running an AI agent that loops thousands of times per run, *I* define each iteration as a step that processes and enqueues its successor, *so that* a million iterations complete with **no gradual slowdown and a flat dead-tuple count** on the hot tables — verifiable with `pg_stat_user_tables.n_dead_tup` staying flat through the run. (The flat-curve claim is scoped to await-light loops; await/join-heavy shapes are characterized honestly in §5.6.)
+
+2. **Long-sleep orchestrator (durable timers).** *As* an engineer modeling a "wait 7 days, then send a reminder" process, *I* call `sleep('7 days')` inside a step, *so that* the workflow durably resumes after the wait **without holding any batch open** and **without a per-workflow polling row** — the sleep is one row in a TRUNCATE-rotated delayed-delivery table, and the woken continuation is **never** misclassified as a stale redelivery and DLQ'd (§5.4.1).
+
+3. **Human-in-the-loop integrator (await external event).** *As* an engineer building an approval flow, *I* call `awaitEvent('approval', timeout => '24h')` and have an **authorized** part of my system call `emit(workflow_id, 'approval', payload, token)`, *so that* the workflow resumes **exactly once** on the event — robust against emit-before-await, await/emit interleave, and emit-racing-the-timeout — or resumes on the timeout branch if the deadline passes first. For approval-class waits the per-wait emit token is **mandatory** (§5.10.2), so the approval cannot be forged by an unauthorized caller (§5.10), nor by guessing or harvesting the `workflow_id` (§5.11), nor replayed without the wait token.
+
+4. **Fan-out batch processor (spawn + join).** *As* an engineer processing a parent job that splits into N independent children (N capped, §5.12), *I* spawn N child workflows and `awaitAll`, *so that* the parent resumes **exactly once** when all N complete — neither zero times (lost-resume race closed, §5.8) nor twice — with a **per-child result array** (success/failure each) materialized in a join-result side table (§5.8) — not inlined in the resume payload — even under redelivery of any child's completion and under concurrent final completers.
+
+5. **Exactly-once integrator (transactional handoff).** *As* an engineer whose step writes a row to *my own* business table and then advances the workflow, *I* run my side effect, the successor enqueue, and the batch ack in **one transaction**, *so that* a crash either commits all three or none — no successor without the side effect, no side effect without the ack, no duplicate handoff.
+
+6. **On-call operator (monitor without a status row).** *As* the engineer on-call for a fleet of running workflows, *I* query the operational views of §5.14, *so that* I can see what is waiting/sleeping/overdue, list everything running right now, and read throughput/failure metrics — **without** the system paying a per-step status-row `UPDATE` to give me that visibility, and with exact per-step liveness available as a single opt-in knob (§5.14.4).
+
+---
+
+## 4. Architecture
+
+<!-- architecture:begin -->
+
+```text
+(architecture not yet specified)
+```
+
+<!-- architecture:end -->
+
+### 4.1 Layering (the sacred boundary)
+
+The durable layer **only calls** the PgQ primitives + `send_at`. It adds **no** modification to rotation/tick/batch logic and introduces **no** second concurrency model. Its dependencies on engine semantics (tick-visibility, durable per-event retry count, `send_at`, the `next_batch` max-events bound) are made explicit and pinned by engine-contract tests (§5.9).
+
+### 4.2 Key abstractions
+
+- **Workflow** — a logical state machine identified by `workflow_id`, which is a **128-bit unguessable capability** (§5.11), not a sequential id. At any instant it is in exactly one of three conditions: **(a)** one *in-flight* message (a step-event sitting in a PgQ batch being processed), **(b)** *scheduled* (a `send_at` continuation awaiting a wake time, or a registered wait awaiting an event), or **(c)** *terminal*. The **single-live-continuation invariant** — each processed step enqueues *exactly one* successor — is what makes exclusivity structural rather than lease-based.
+- **`workflow_id` — addressing handle AND bearer capability.** It is used both to *address* a workflow (in payloads, user tables) and, combined with the role grants and per-wait tokens of §5.10, to *authorize* operations against it. Because it does double duty it must be treated as a secret; §5.11 specifies its confidentiality/leakage model (hashed at rest in audit/DLQ, never logged raw, mandatory token for approval waits).
+- **Step-event** — the message on the PgQ queue. Payload carries: `workflow_id`, `step_seq` (monotonic progress anchor), `step_name`/state tag, `delivery_anchor` (the event's deliverable time, §5.4.1), small continuation state (continuation-passing), and — for retries — `retry_attempt`/`origin_step` (§5.2), subject to a **hard payload size cap** (§5.12). `workflow_id`/`step_seq`/`step_name` are also placed in `ev_extra1/2/3` for indexed observability (§5.14.2). Large state is the user's responsibility to hold in their own tables, addressed by `workflow_id`.
+- **Transition** — process a step → emit successor as a *new append*. Never an `UPDATE` of a status row.
+- **Coordination side tables** (the only mutable state; see §5.5) — `wf_registry`, `wf_wait`, `wf_event_cache`, `wf_join`, `wf_join_done`, `wf_dedup`, `wf_audit`, the consumer-wide `wf_dispatch_control` (one row per logical consumer, §5.2), and the **optional, opt-in** `wf_live` projection. Their churn is bounded by **concurrency and coordination-point count, not total step volume** — stated precisely (distinguishing live row-count from dead-tuple rate, and conceding the await/join-heavy case) in §5.6.
+
+### 4.3 Concurrency / ownership model
+
+One **logical consumer** with cooperative **subconsumers** splitting batches (PgQ 0.2 feature). Because exactly one live message exists per workflow, only one subconsumer ever touches a given workflow at a given instant — exclusivity is an emergent property of the invariant, requiring **no claim/lease/steal machinery**. Worker death mid-batch is covered by PgQ's existing cooperative `dead_interval` takeover: the unfinished batch is reassigned and the in-flight step redelivers (at-least-once), made safe by per-step idempotency (§5.4) whose dedup horizon is bounded ≥ max single-attempt redelivery latency (§5.4.1). **Because there are multiple concurrent subconsumers, any dispatcher control that must be uniform across the logical consumer — specifically the poison-pill `max_events` reduction (§5.2) — is held in the shared, consumer-wide `wf_dispatch_control` row, not in process-local dispatcher state.**
+
+---
+
+## 5. Implementation details
+
+### 5.1 The hot path: one transition = append + ack, atomically
+
+The foundational guarantee. `insert_event()` (enqueue successor) and `finish_batch()` (ack) run in the **consumer's own transaction**. **The atomic commit unit is the batch transaction** (§5.2); for the common case of a single-event batch it reduces exactly to one step's side effects + its successor enqueue + its ack committing together:
+
+```
+begin;
+  -- 1. step's own DB side effects (idempotent or naturally in-txn)
+  -- 2. record per-step dedup marker (workflow_id, step_seq)   [if first delivery]
+  perform pgque.insert_event(queue, next_state);   -- enqueue exactly one successor
+  perform pgque.finish_batch(batch_id);            -- ack this batch
+commit;
+```
+
+- **Commit** ⇒ successor durably enqueued **AND** batch finished, atomically ⇒ exactly-once handoff.
+- **Crash before commit** ⇒ txn aborts ⇒ no successor, no dedup marker, batch not finished ⇒ the step redelivers cleanly.
+
+The dedup marker is keyed on *this attempt's* `(workflow_id, step_seq)`. A retry continuation is a **new transition with a fresh `step_seq`** (§5.2), so it carries its own marker and is therefore **not** absorbed as a dedup no-op — it re-executes. **No subtransactions are used on this path** (hard constraint; also §5.13).
+
+### 5.1.1 The make-or-break rebuttal: "isn't per-workflow state a per-transition UPDATE, 1:1 with messages → same bloat?"
+
+The single most important objection, answered head-on. **No** — and the reason is the same batching amortization that makes PgQ itself cheap:
+
+- **PgQ's own mutable state is the `subscription` (consumer-position) row, updated per *batch*, not per *event*** — amortized N× by batching, and **zero** updates when there is nothing to consume. That is exactly why PgQ is low-bloat.
+- **The workflow dispatcher IS a PgQ consumer**, so it inherits that property unchanged: one `subscription` `UPDATE` per tick/batch, amortized over all the (many different workflows') transitions in that batch, idle = zero. This row is **one-per-consumer**, ~tick-rate, HOT-updatable — it does **not** scale with workflow count or transition count.
+- **Per-workflow state is carried in the in-flight message (continuation-passing), NOT in a per-workflow row.** Advancing workflow W from step n→n+1 is an **append** (enqueue successor with `step_seq+1`); the old message is consumed and rotates away. There is **no per-workflow position row `UPDATE`d per transition.** So "N workflows × M steps" = N×M **appends** to the rotating queue (zero bloat) + the *same* per-batch `subscription` update PgQ already does. It is **not** N×M row `UPDATE`s.
+- **Dedup markers `(workflow_id, step_seq)` are INSERTs (appends) to a rotating short-horizon table, not UPDATEs.**
+- The ONLY way to reintroduce per-transition `UPDATE` churn is a live "current step" projection updated every step — which is exactly why `wf_live` is **opt-in, default OFF**, and never on the correctness path (§5.5/§5.14.4).
+
+### 5.2 Dispatch loop, transaction boundary, and retry
+
+**The transaction boundary is the batch.** PgQ acks a *batch* wholesale via `finish_batch`; there is no per-event ack. The dispatcher processes every event in a batch within **one** transaction and commits once:
+
+```
+loop:
+  K        := dispatch_control.current_max_events           -- shared, consumer-wide (§5.5)
+  batch_id := pgque.next_batch(queue, consumer, max_events := K)   -- snapshot-bounded, ≤ K events
+  if batch_id is null:
+      run_timeout_sweep()                              -- §5.7.1 in-loop liveness
+      sleep to next tick; continue
+  events  := pgque.get_batch_events(batch_id)
+  begin
+    for each event in events:                          -- batch step execution
+        if redelivery_age(event) > dedup_horizon:      -- §5.4.1 staleness GATE, BEFORE body
+            route_to_dlq(event); continue              --   route-not-process: no user body runs
+        advance_one(event)                             -- §5.3, appends successor(s)
+    pgque.finish_batch(batch_id)
+    run_timeout_sweep()                                -- opportunistic
+  commit
+  on abort:  note_batch_abort()                        -- ramps dispatch_control down (below)
+  on clean commit at K=1:  note_clean_isolated_commit() -- ramps dispatch_control back up
+```
+
+**Batch size is bounded** (the `max_events := K` dispatch parameter, default small) so the blast radius of any rollback is bounded and the single-event reduction of §5.1 is the common shape. **`K` is read from the shared `wf_dispatch_control` row, not from process-local state** — see the poison-pill quarantine below.
+
+**Per-event retry without subtransactions.** The v0.1 claim that a transiently failing step "calls `event_retry()` for that single event rather than aborting the whole batch" is **incorrect under the stated constraints** — PL/pgSQL cannot catch an error and continue the surrounding transaction without a savepoint, and **§5.1/§5.13 forbid subtransactions in hot paths** (the no-subtransaction rule lives in §5.1/§5.13). Two failure channels:
+
+1. **Expected / transient failure → returned retry continuation (an append, not a throw).** A step that wants to retry re-enqueues a continuation of the *same logical step* via `send_at` with backoff and finishes normally. **The retry continuation is a NEW transition carrying a fresh `step_seq`** (with `retry_attempt` and `origin_step` recorded in the payload). Because its `step_seq` is new, the §5.4 dedup logic does **not** treat it as a committed no-op — the retried step **re-executes its body** on delivery. After `max_retries` the step returns a **DLQ transition** (an append to the DLQ queue) rather than throwing. This path is subtransaction-free and does **not** abort the batch.
+2. **Unexpected exception (genuine bug, OOM, lost connection) → batch aborts and the whole batch redelivers.** Rare, correct, and safe: redelivery is idempotent (§5.4). **Poison-pill containment — consumer-wide coordinated `max_events` reduction (subconsumer-safe):** the durable layer **cannot** durably write a per-workflow exception counter from the aborting transaction (the abort discards it) and PgQ delivers batches as snapshot-bounded ranges, not per-workflow-selectable. Containment therefore rests on two mechanisms that need **no engine change and no sub-range partial ack**:
+   - (a) **the engine's durable per-event retry counter**, which PgQ increments across redeliveries and uses to route an over-threshold event to the DLQ — pinned as engine contract #2 (§5.9); and
+   - (b) **consumer-wide batch-size reduction on the existing `next_batch` max-events bound (engine contract #4, §5.9), coordinated through the shared `wf_dispatch_control` row.** On detecting an aborting batch, a subconsumer's `note_batch_abort()` **lowers `current_max_events` in `wf_dispatch_control` (down to 1) in its own short committed transaction** — this write survives the batch abort because it is a *separate* committed transaction, not the aborted one. Because the bound lives in a **single consumer-wide row read by every subconsumer at the top of its loop**, the reduction is uniform across all subconsumers, not process-local. Once `current_max_events = 1`, every subconsumer requests size-1 batches, so the unfinished poison event — **whichever subconsumer it is redelivered to** — arrives in its **own size-1 batch**, aborts **only a batch containing itself**, and crosses the engine retry threshold (contract #2) **in isolation**, landing in the DLQ. An innocent event that merely shared the original larger batch is re-processed (idempotently, §5.4) and **commits on its own size-1 redelivery** rather than being dragged to the DLQ.
+
+   **Why this is subconsumer-safe.** A naive design that set `max_events` in process-local dispatcher state would let a subconsumer that had not itself aborted redeliver the poison event re-aggregated with K−1 innocents at `max_events = K`. Moving the bound into the shared `wf_dispatch_control` row fixes this: the first abort writes `current_max_events = 1` for the **whole logical consumer**, and every subconsumer reads it before its next `next_batch`, so no subconsumer re-aggregates the poison during the quarantine window. The row is **one-per-logical-consumer** (not per workflow, not per event), HOT-updatable, written only at abort/recovery transitions (≈abort-rate, rare) — it does **not** scale with workflow or transition count and is **not** a per-key coordination row of the kind §5.5 removed.
+
+   **Quarantine recovery (the up-ramp — `max_events` restoration policy).** The down-ramp alone would permanently collapse throughput to one-event-per-batch after a single transient abort. Recovery is explicit: after `note_clean_isolated_commit()` observes **`quarantine_cooldown` consecutive clean size-1 commits across the consumer** (a configurable count, default small — long enough that the poison event has crossed the engine retry threshold and been DLQ'd in isolation), `wf_dispatch_control.current_max_events` is restored to the configured `K`. Restoration is gated on the cooldown count, **not** time, precisely so the poison is quarantined to the DLQ *before* batches re-aggregate; restoring too eagerly (before the threshold is crossed) is what the cooldown prevents. The cooldown counter is held in the same `wf_dispatch_control` row and advanced under a per-row lock so concurrent subconsumers count monotonically.
+
+   **Honest bound on co-tenant impact.** Before the consumer-wide bound reaches 1, innocent co-tenants in an aborting batch do accrue a *bounded* number of retry-counter increments and idempotent re-processings (bounded by the configured starting `K` and the one-step drop to 1). Once isolated at size 1 they commit independently. We do **not** claim zero co-tenant disturbance — only that no innocent co-tenant is forced to the DLQ by the poison event, and that the isolation holds **across all subconsumers**, not just the one that first aborted.
+
+A batch may still contain step-events for many distinct workflows advancing in one transaction (native fan-out); correctness no longer depends on per-event mid-transaction error recovery.
+
+### 5.3 The five durable-execution requirements, mapped
+
+1. **Exclusive ownership — structural.** Single-live-continuation invariant + cooperative `dead_interval` takeover. No lease.
+2. **Mutable run state — re-enqueue, don't update.** Each transition appends a new event carrying new state; small state rides the payload; no long-lived per-run row on the hot path.
+3. **Long-lived persistence — rotating `send_at`.** `sleep('7d')` = `send_at(continuation, now()+7d)`; the step acks immediately; the sleep is one row in a TRUNCATE-rotated delayed table — zero-bloat, never an open batch. The woken continuation's `delivery_anchor` is its wake time, so it is never confused with a stale redelivery (§5.4.1).
+4. **Per-row scheduling.** Timers via rotating `send_at`. **`awaitEvent` with timeout** is the genuinely hard new piece (§5.7).
+5. **Checkpoint replay — not needed.** No long-running function to resume. Recovery = PgQ's at-least-once redelivery of the single in-flight step. Correctness = exactly-once handoff (§5.1) + per-step idempotency (§5.4).
+
+### 5.4 Per-step idempotency
+
+Every step attempt is keyed `(workflow_id, step_seq)`. On (re)delivery a step first checks/inserts a dedup marker; the marker insert and the successor enqueue commit together (§5.1). A redelivered step **with the same `step_seq`** whose successor already committed is a no-op (marker present) and simply re-acks. A **retry continuation has a fresh `step_seq`** (§5.2) and therefore re-executes — it is a new attempt, not a redelivery of the prior one. The dedup store is append-based and short-horizon (rotating) so it does not itself become a bloat source (§5.6).
+
+#### 5.4.1 The dedup-horizon bound and the delivery-anchor clock
+
+Exactly-once handoff holds **iff the dedup horizon ≥ maximum single-attempt redelivery latency**. The clock the horizon is measured against is the **`delivery_anchor`**, carried in the payload, defined as the time the event *became deliverable* — its tick-visibility time, and for a `send_at` continuation its **scheduled wake time `now()+Δ`, NOT the time the continuation was created**. Redelivery age = `now − delivery_anchor`, evaluated **per-event/per-transition** and **reset at every transition and every timer fire**. Consequences:
+
+- A freshly woken `sleep('7d')` continuation has `delivery_anchor` = its wake time, so its redelivery age on first delivery is ~0 — it is **never** confused with a 7-day-stale redelivery. The long wait lives in the gap between *creation* and *delivery anchor*, which the horizon does not see.
+- Only repeated redelivery of the *same* deliverable event (takeover/retry of one attempt) advances age against the horizon.
+
+Bound (note: single-attempt, **not** cumulative-over-retries, and **independent of max sleep**):
+```
+dedup_horizon  ≥  max_retry_backoff        (one attempt's backoff)
+               +  dead_interval             (worst-case takeover delay)
+               +  max_batch_duration
+               +  safety_margin
+```
+It does **not** include `max_sleep` (re-anchored above) nor `max_retries × backoff` (each retry is a fresh transition with its own `step_seq` and `delivery_anchor`, §5.2, so it never ages against the prior attempt's marker). The horizon is configured and validated at install against `dead_interval`, `max_retry_backoff`, and `max_batch_duration`.
+
+**Enforcement — and its ordering relative to the body.** The staleness check is a **pre-body dispatcher gate**: in the dispatch loop (§5.2) it runs **before `advance_one` executes any user step body**. Any deliverable event whose redelivery age (`now − delivery_anchor`) exceeds the horizon is **routed to the DLQ instead of processed** — a *route-not-process* decision that runs **no user body and therefore cannot abort**, so its DLQ routing commits cleanly with the surrounding batch transaction (or, if a co-tenant in the same batch later aborts, the event is simply re-gated and re-routed on redelivery — the route decision is idempotent and side-effect-free). Because the staleness gate runs first and never executes the body, a stale event is never handed to a body that would abort; the gate reliably quarantines genuinely-stale events. This makes a marker unable to rotate out underneath a still-live redelivery and silently report "first delivery."
+
+**Reconciling the two DLQ-routing mechanisms.** There are two distinct routes to the DLQ, operating at different points, so they do not conflict:
+  - **§5.4.1 staleness gate** fires on `now − delivery_anchor > dedup_horizon`, **before** the body runs, commits cleanly (route-not-process). It quarantines an event whose marker may have rotated away — a *correctness* guard against silent double-handoff.
+  - **§5.2 / contract #2 engine retry counter** fires when a *body that actually ran and aborted* crosses the engine's per-event retry threshold — a *poison-pill* guard for the aborting-batch channel.
+  The "only durable counter available to the aborting-batch channel" claim (§5.2) is scoped exactly to that channel: **after a user body has run and aborted its transaction**, the durable layer has discarded any state it tried to write, so the *engine* retry counter is indeed the only durable signal left for the abort path. The §5.4.1 gate is **not** part of the aborting-batch channel — it commits before any body runs — so it does not contradict that claim. For a poison event redelivered repeatedly in size-1 batches, the staleness gate fires first **only if the event also goes stale**; if it is processed promptly each redelivery (typical), the staleness clock stays under the horizon and contract #2's retry threshold is the route that fires — exactly as intended. Property tests (§6.2) assert **both** directions: no double-handoff at horizon-boundary redelivery age, AND a `sleep` longer than the horizon resumes normally and is **not** DLQ'd; and §6.3 asserts the gate-runs-before-body ordering.
+
+### 5.5 Coordination side tables
+
+| Table | Role | Churn driver | Lifecycle |
+|---|---|---|---|
+| `wf_registry` *(mandatory)* | minimal authoritative live-workflow set (id + status); source of truth for emit-liveness (§5.10.2) and unknown-id rejection (§5.12) | concurrency (live count) | `INSERT` on `start_workflow`, `DELETE` on terminal — one insert + one delete per workflow *lifetime*, not per step |
+| `wf_wait` | registered event waits, single-resume token, optional per-wait emit token | open awaits | `DELETE … RETURNING` on resume/timeout |
+| `wf_event_cache` | first-write-wins cache for emit-before-await | emit/await coordination points | bounded by `cache_retention_horizon` (§5.7.2), never silent-drop within horizon |
+| `wf_join` | join row: parent + total N, single-resume token | spawn points | deleted when parent resumes |
+| `wf_join_done` | idempotent completed-set `(parent, child_idx)` **carrying each child's result value/marker** (§5.8 result-array spill) | child completions (≤ concurrency × fanout) | dropped with the join |
+| `wf_dedup` | per-attempt `(workflow_id, step_seq)` markers | redelivery horizon | rotating / short-horizon, bound per §5.4.1 |
+| `wf_audit` | append-only log of security-relevant actions (§5.10.3); also the historical-metrics source (§5.14.3) | emit/resume/spawn events | rotating (TRUNCATE), exported before rotation |
+| `wf_dispatch_control` *(mandatory)* | **one row per logical consumer**: shared `current_max_events` + quarantine cooldown counter coordinating the §5.2 poison-pill batch-size reduction across all subconsumers | abort/recovery transitions (≈abort-rate, NOT per step/workflow) | one persistent row per consumer; HOT-updated in place under a per-row lock; never grows with workflow or transition count |
+| `wf_live` *(optional, opt-in, default OFF)* | rich current-state projection for observability only — never required for correctness | concurrency (live count) | **one row per LIVE workflow**, HOT-`UPDATE`d in place (boundary-rate by default — start/park/terminal; per-step in opt-in high-resolution mode), `DELETE`d on terminal. Live row-count is concurrency-bounded; dead-tuple rate = its update rate (per-step `UPDATE` cost only in high-res mode). |
+
+**`wf_live` model, stated once and consistently.** `wf_live` is a **one-row-per-live-workflow HOT-`UPDATE`d projection**, *not* an append+rotate stream. Its **live row-count is concurrency-bounded** (one row per live workflow, deleted on terminal — agreeing with §4.2 and §5.6). Its **dead-tuple generation rate equals its update frequency**: at *boundary granularity* (default — start/park/terminal) that is coordination-rate; in the *opt-in high-resolution mode* it is one HOT-`UPDATE` per step — the documented per-step write cost, HOT-optimized, one row/workflow, still bounded by concurrency in row-count. An earlier "append-based, rotating, not insert+delete" description was **withdrawn** as inconsistent with §4.2/§5.6 and with the opt-in-per-step-`UPDATE` design from the idea; `wf_live` is the single knob where the user may *choose* to pay per-step writes for exact liveness. It is never on the correctness path.
+
+**No persistent per-key lock table exists.** The await/emit serialization of §5.7.3 and the join-completion serialization of §5.8 both use *transaction-scoped advisory locks* (no row), so they contribute zero live or dead tuples. `wf_registry`, `wf_wait`, `wf_join` are deleted on resolution (row-count bounded by concurrency); `wf_event_cache`, `wf_dedup`, `wf_audit` are horizon/rotation-bounded; `wf_dispatch_control` is a single fixed row per consumer.
+
+### 5.6 The honest zero-bloat / stays-fast claim (row-count vs dead-tuple rate, incl. the await/join-heavy case)
+
+Zero-bloat — and therefore the user-facing "stays fast under sustained load" outcome (§1) — holds on the **hot step-transition path** (appends + rotation). The same per-batch amortization that makes PgQ cheap is preserved, because the workflow dispatcher **is** a PgQ consumer and per-workflow state lives in the in-flight message, not a mutated row (§5.1.1): "N workflows × M steps" = N×M **appends** to the rotating queue + the *same* one-per-batch `subscription` update PgQ already does (amortized over every workflow advancing in that batch; zero when idle) — **not** N×M row `UPDATE`s. For coordination, the spec separates two quantities and concedes a workload class:
+
+- **Live row-count** is bounded by **concurrency** (`wf_registry`, `wf_wait`, `wf_join`, and the optional `wf_live` all hold ~one row per live coordination point/workflow; `wf_dispatch_control` is one fixed row per consumer).
+- **Cumulative dead-tuple generation rate** is bounded by **coordination-point throughput**, because every resolution is a `DELETE` (`wf_registry` on terminal, `wf_wait`/`wf_join` on resolve), plus `wf_live`'s update rate if it is enabled.
+
+**Concession (await/join-heavy workloads).** For a workflow that awaits an event or spawns/joins on (nearly) *every* step — a normal shape for human-in-the-loop and tool-calling agent loops, both named primary personas — that is on the order of one `DELETE` per step, i.e. the **same order** of dead-tuple generation as the per-step status-row `UPDATE` the pitch eliminates. We therefore **scope the headline**: the flat-dead-tuple curve is claimed for **await-light loops** (the bulk of high-iteration agent inner loops, which transition far more often than they coordinate). For coordination-heavy workloads we claim only **bounded live row-count** and a dead-tuple rate proportional to *coordination points*, mitigated by rotation where feasible (`wf_dedup`, `wf_event_cache`, `wf_audit` rotate; `wf_registry`/`wf_wait`/`wf_join` are small and rely on documented required autovacuum settings, §10). The precise marketed claim is: **stays-fast hot path with zero dead-tuple growth; coordination tables have concurrency-bounded *live* row-count and coordination-point-bounded *dead-tuple rate* — flat for await-light loops, and for await/join-heavy loops bounded by coordination throughput rather than total step volume, still well-managed but not zero.** The benchmark (§6.5) publishes the coordination-table dead-tuple curve and includes an explicit **await/join-heavy A/B** vs the mutable-status baseline so the scoped headline is substantiated for the personas that stress coordination. We never claim "zero dead tuples anywhere."
+
+### 5.6.1 Honest latency characterization (separate from bloat)
+
+A single workflow advances **one step per tick round-trip** (the successor is visible only at the next tick), so one *sequential* workflow runs at ~tick-rate (e.g. ~10 steps/s at a 100 ms tick). The "millions of iterations" / "tens of thousands of transitions/sec" headline is **aggregate across many concurrent workflows**, not one workflow doing a million sequential steps. For LLM-agent loops (tens of steps, each gated by a slow model call) this is a non-issue. A single hot CPU loop that needs more than tick-rate should batch several iterations inside one step before checkpointing. We state this plainly so the throughput claim is not misread as single-workflow sequential rate.
+
+### 5.7 `awaitEvent` / `emit` — the ~20% with real risk (designed and TDD'd first)
+
+Wait registry keyed `(workflow_id, event_name)`, event names **correlation-scoped** and `workflow_id` an unguessable, confidentiality-protected capability (§5.11). Race table:
+
+- **emit-before-await** → `emit` writes `wf_event_cache` **first-write-wins**; a later `awaitEvent` finds the cached event and resumes immediately (no wait row created). The cache entry is retained for the full **`cache_retention_horizon`** (§5.7.2), never evicted under it. (emit is rejected for non-live ids per §5.10.2/§5.12.)
+- **await/emit interleave** → both serialize on a **transaction-scoped advisory lock** keyed on `(workflow_id, event_name)` (§5.7.3), so exactly one of {register-wait, consume-cache} wins deterministically and the mechanism is safe under transaction-pooling poolers.
+- **double-resume (emit racing the timeout sweep)** → the wait row is a **single-resume token** resolved by `DELETE … RETURNING` in the **same txn** as the continuation enqueue. Whoever deletes first (emit or sweep) resumes; the loser sees zero rows and does nothing.
+- **stale / cross-talk cached events** → correlation-scoped names + capability `workflow_id` + bounded-horizon GC.
+- **redelivery of the await step itself** → idempotent registration on `(workflow_id, step_seq)`; re-registering is a no-op.
+- **timeout** → injected by the in-loop timeout sweep (§5.7.1), via the same single-resume `DELETE … RETURNING` path.
+
+#### 5.7.1 Timeout liveness, and the operator invariant it requires
+
+Every dispatcher iteration — including the idle tick-sleep path — calls `run_timeout_sweep()` (bounded batch of due timeouts), so **as long as a dispatcher is running**, timeouts fire without pg_cron. **However, this does not cover the no-running-dispatcher state.** A low-volume approval system (the §3.3 persona) that autoscales workers to **zero** between events, or one where all workers have crashed and not yet restarted, has *no* loop iterating, so a 24h timeout would fire only whenever a worker next starts — arbitrarily late. The spec surfaces this as a **hard operator invariant rather than hiding it**:
+
+> **Timeout liveness requires either (a) a continuously-running dispatcher, or (b) pg_cron driving `run_timeout_sweep()` on a fixed cadence.** For scale-to-zero / serverless topologies (RDS/Aurora/Cloud SQL/Supabase/Neon with app workers that scale to zero), **pg_cron is REQUIRED**, not optional. The install/ops docs (§10) state this as a deployment precondition and the install script warns if neither a long-running dispatcher nor pg_cron is configured.
+
+pg_cron remains an *optimization* only for the always-on-dispatcher topology; it is a *correctness requirement* for scale-to-zero. A crash/idle-recovery test (§6.3) asserts the running-dispatcher path with pg_cron disabled, and a separate test asserts the scale-to-zero path fires via pg_cron.
+
+#### 5.7.2 Two distinct horizons (separated)
+
+- **`cache_retention_horizon`** — how long an emit-before-await entry lives in `wf_event_cache`. It need only cover the **emit→await-registration gap**: the time for an in-flight workflow to reach and register its `awaitEvent` after an emit (queue backlog + redelivery + max batch duration). This is small and bounded by processing latency, **not** by any user timeout. GC only evicts entries older than this horizon; within it an event is never dropped.
+- **`await_timeout`** — the user-facing await→event deadline (e.g. 24h in story §3.3, or a legitimate multi-day approval wait). This is **independent of cache retention** and is **not** capped by it. An `awaitEvent` with a long deadline is fully supported; the deadline governs the timeout-sweep firing (§5.7.1), not cache eviction.
+
+Thus a 24h await behind a 1-second emit-before-await is never rejected: the cache only had to survive the sub-second registration gap, while the 24h deadline is tracked by `wf_wait` + the sweep. The two horizons, the cache cardinality cap (§5.12), and the dedup horizon (§5.4.1) are validated for mutual consistency at install.
+
+#### 5.7.3 Locking mechanism pinned (pooler-safe, zero-row)
+
+The await/emit key is serialized with a **transaction-scoped advisory lock**, `pg_advisory_xact_lock(hashtextextended(workflow_id || ':' || event_name, 0))`, held only for the enclosing transaction (auto-released on commit/abort) and therefore **safe under PgBouncer transaction pooling**. It leaves **no persistent row**. Hash collisions between unrelated `(workflow_id, event_name)` pairs are **correctness-safe**, not bugs: a collision only causes transient false serialization of two unrelated keys, because the *decisive* operation under the lock is an atomic `INSERT … ON CONFLICT DO NOTHING` (register wait) / `DELETE … RETURNING` (consume cache or resume) on the **exact** key. **Session-level advisory locks (`pg_advisory_lock`) remain explicitly forbidden** (pooler-unsafe); only the transaction-scoped variant is permitted.
+
+### 5.8 fan-out / join (spawn + `awaitAll`)
+
+- Spawn N children (N **capped**, §5.12) with **distinct child workflow ids** (each an unguessable capability); **record the join total `N` atomically with the spawn**.
+- **Engine contract (§5.9):** children become visible only at the next tick boundary, *after* the join row is committed; this tick-visibility ordering makes the join-total recording race-free. Pinned by a regression test.
+- Count completions with an **idempotent completed-set** `(parent, child_idx)` in `wf_join_done` — redelivery-safe.
+- **Completion serialization — closes the lost-resume race.** Counting completions is **not** left to bare `INSERT`-then-`COUNT` under READ COMMITTED, which would let the final two concurrent completers each observe `count < N` (neither seeing the other's still-uncommitted insert) and **neither** flip to N — a *lost resume* (parent stuck forever). Instead, each completing child, after writing its `(parent, child_idx)` row, serializes the count-and-resume decision on the **`wf_join` row** via a per-join lock — `SELECT … FOR UPDATE` on the `wf_join` row (equivalently `pg_advisory_xact_lock` on the join id). Holding that lock it re-counts `wf_join_done`; the completer that observes the count reach `N` deletes the `wf_join` row (single-resume token) and enqueues the parent continuation, **all in one transaction**. Because the per-join lock totally orders the final completers, the count is observed monotonically and **exactly one** completer sees `N` — guaranteeing the parent resumes **exactly once: neither zero (liveness) nor twice (safety)**.
+- **Isolation level pinned.** The dispatch/join transaction runs at **READ COMMITTED**; correctness of the join count does **not** depend on a higher isolation level because the per-join serialization lock makes "insert my completion + re-count + (maybe) resume" atomic with respect to other completers of the same join.
+- **Per-child result spill.** Each child writes its **result value or failure marker into its `wf_join_done` row**, keyed `(parent, child_idx)`. The parent's resume continuation payload carries **only a reference** (the parent `workflow_id`/join id), **never the inlined N-entry array** — so the 8 KiB payload cap (§5.12) is respected even at `max_spawn_fanout = 1024`. The SDK's `awaitAll` reads the assembled result array from `wf_join_done` addressed by join id. This is concurrency×fanout-bounded coordination state (dropped with the join), **not** per-step mutable state and **not** a status row.
+- **Explicit per-child failure semantics**: the parent receives a **result array**, one entry per child (success value or failure marker). A failed child does not block the join; it reports failure in its slot.
+- **Cancellation / orphan handling is explicitly deferred** (§12).
+
+### 5.9 Engine contracts (explicit coupling, pinned)
+
+The durable layer depends on four specific PgQ behaviors. Because the engine is sacred and unmodified, the durable layer cannot pin them from inside the engine; it states them as **explicit contracts** and ships **engine-contract regression tests** (§6.3) that fail loudly on violation:
+
+1. **Tick-visibility ordering** — events inserted before tick T are not visible in any batch until a tick ≥ T+1, and a committed side-table row written in the same transaction as an `insert_event` is visible to any consumer that later sees that event. (Underpins snapshot-batch isolation and §5.8 join atomicity.)
+2. **Durable per-event retry count + DLQ routing** — PgQ maintains a per-event retry counter that survives redelivery (including after a wholesale batch abort) and routes an over-threshold event to the DLQ. (Underpins the §5.2 poison-pill quarantine; this is the *only* durable counter available to the aborting-batch channel — scoped per §5.4.1.)
+3. **`send_at` delayed delivery** — `send_at(event, t)` makes the event deliverable at `t` over a TRUNCATE-rotated delayed table. (Underpins `sleep`, retry backoff, and the `delivery_anchor` semantics of §5.4.1.)
+4. **`next_batch` honors a caller-supplied max-events bound** — `next_batch(…, max_events := K)` returns a batch of at most `K` events (down to `K = 1`), and events left unfinished by an aborted batch are redelivered subject to that bound on subsequent calls **by any subconsumer**. (Underpins the §5.2 poison-pill **size-1 isolation**; this is a property of the existing `next_batch` API, not a new sub-range/partial-ack primitive. Note: the *coordination* of the bound across subconsumers is the durable layer's own `wf_dispatch_control` row, §5.2 — the engine contract is only that each individual `next_batch` call honors the `K` it is passed and that unfinished events remain redeliverable to whichever subconsumer next calls.)
+
+A minimum PgQ engine version/feature floor is required and gated at install (§5.13, §10): `send_at` (PR #237) present, the durable per-event retry counter exposed, tick-visibility behaving per contract #1, and `next_batch` honoring the `max_events` bound per contract #4. Install **fails loudly** if the floor is unmet.
+
+### 5.10 Authorization & the SECURITY DEFINER surface
+
+The v0.1 spec left the SECURITY DEFINER surface unguarded — functions default to `EXECUTE` granted to `PUBLIC`, so any role with a connection could call `emit`/`spawn`/`finish` against any workflow, directly forging approvals (§3.3). The spec specifies a concrete authorization model.
+
+#### 5.10.1 Default-deny grants
+
+The install script **`REVOKE EXECUTE … FROM PUBLIC`** on every durable function, then grants explicitly to two dedicated roles:
+
+- `pgque_durable_worker` — may call dispatch/internal functions (`next_batch` wrappers, `finish_batch` wrappers, timeout sweep, join resolution, `wf_dispatch_control` updates). Granted to the worker/consumer role only.
+- `pgque_durable_client` — may call the producer-facing surface (`emit`, `spawn`, `start_workflow`). Granted to application roles that legitimately drive workflows.
+
+Internal-only functions (token resolution, dedup, projection) are granted to **neither** and are callable only as `SECURITY DEFINER` internals invoked by the above. A CI grant-audit test asserts no durable function retains a `PUBLIC` execute grant.
+
+#### 5.10.2 Caller-scoped emit authorization (and the liveness source)
+
+Being able to call `emit` is necessary but not sufficient: the caller must also possess the target workflow's **`workflow_id` capability** (§5.11), and `emit` must verify the id is live. **The authoritative liveness source is the mandatory `wf_registry` table (§5.5), not the optional `wf_live` projection.** **`emit(workflow_id, event_name, payload, token?)` succeeds only if the `workflow_id` matches a live row in `wf_registry`**; emits for unknown ids are rejected without creating a cache row (§5.12).
+
+Note on emit-before-await: a workflow is `INSERT`ed into `wf_registry` at `start_workflow` for its **entire lifetime** (§5.5), so any workflow that can legitimately receive an emit — including before it has reached its `awaitEvent` — is **already** a live `wf_registry` row. Registry membership fully covers the emit-before-await case; **no separate "pre-registration" record exists.**
+
+**Per-wait emit token — MANDATORY for approval-class waits.** For high-assurance waits (approvals, escalations), `awaitEvent` issues a per-wait emit token stored in `wf_wait`, and the matching `emit` **must** present it. Holding the `workflow_id` alone is therefore **insufficient** to satisfy an approval wait — directly mitigating capability leakage (§5.11). For low-assurance waits the token is optional. All `SECURITY DEFINER` functions pin `search_path = pgque, pg_catalog`.
+
+#### 5.10.3 Audit trail (claims corrected; attribution made useful under pooling)
+
+Security-relevant actions — `emit`, wait-resume, `spawn`, timeout-resolution — append a row to the **append-only, rotating `wf_audit`** table. The spec corrects two v0.2 overclaims:
+
+- **No "tamper-evident" claim.** The table is **append-only by convention within the durable role's trust boundary** — the owning/superuser role can `DELETE`/`TRUNCATE`, and an attacker who can trigger rotation or stall the export hook can erase the pre-export window. We claim only an *append-only operational audit log*, not cryptographic tamper-evidence. **Hash-chaining / signing is a deferred enhancement (§11)**.
+- **Attribution that survives pooling.** Recording `db_role = session_user/current_user` is near-useless under the spec's target deployment: under `SECURITY DEFINER`, `current_user` is the definer/owner, and under PgBouncer transaction pooling with a shared `pgque_durable_client` role, `session_user` is that one shared role. The spec therefore records an **application-supplied `actor_id`** (passed explicitly by the client on `emit`/`spawn`), alongside `db_role`, `txid`, and `event_time`. The `actor_id` is the forensic anchor; `db_role` is retained for defense-in-depth. Documented limitation: `actor_id` is only as trustworthy as the calling application's own authentication.
+- **`workflow_id` is stored hashed**, not raw (§5.11), so the audit log is not itself a capability-leakage vector.
+
+The table is TRUNCATE-rotated to preserve zero-bloat and exported to durable storage before each rotation so the trail survives (it doubles as the historical-metrics source, §5.14.3).
+
+### 5.11 `workflow_id`: unforgeable AND confidential
+
+Every `workflow_id` (parent and child) is a **128-bit cryptographically random value** (`gen_random_uuid()` / `pgcrypto`), never a sequential or queue-derived id — so an attacker cannot enumerate ids to drive, resume, or race-to-timeout arbitrary workflows. Because the same value is both a bearer capability and an addressing handle copied into step-event payloads, `wf_audit`, user tables, external emitters, **DLQ'd payloads**, and error/log surfaces (`pg_stat_activity`, statement-parameter logging, exception messages), it must be treated as a secret. Leakage model and mitigations (all required):
+
+1. **Mandatory per-wait emit token for approval-class waits (§5.10.2).** Primary mitigation: a harvested `workflow_id` alone **cannot** forge an approval — the wait token, issued only to the legitimate awaiter, is also required.
+2. **Hashed at rest in lower-trust stores.** `wf_audit` and DLQ payloads store a salted hash / truncated reference of `workflow_id`, not the raw capability.
+3. **Never logged raw.** Durable functions do not pass `workflow_id` as a logged statement parameter; ops docs (§10) require disabling parameter logging for the durable schema; exception messages reference the hashed id.
+4. **CSPRNG generation (testable form).** The id column is **defaulted by `gen_random_uuid()`/`pgcrypto`**, and CI **statically rejects any code path that derives `workflow_id` from a sequence/serial/queue offset** — this is the testable assertion (§6.2 item 6).
+
+The spec states explicitly: **the security of every coordination primitive rests on `workflow_id` being both unforgeable and confidential; approval-class authority additionally rests on the per-wait emit token, so id confidentiality is defense-in-depth rather than the sole barrier.**
+
+### 5.12 Resource limits (anti-bloat / anti-DoS caps)
+
+- **Spawn fan-out:** `spawn(...)` enforces `N ≤ max_spawn_fanout` (configurable, default 1024). Exceeding it is a loud error. (Per-child results spill to `wf_join_done`, §5.8.)
+- **Payload size:** the "small continuation state" convention is a **hard cap** (`max_payload_bytes`, default 8 KiB) enforced at `insert_event`-wrapper time; oversized payloads are rejected. Large state and join result arrays belong in side tables addressed by `workflow_id`/join id.
+- **emit cardinality / unknown-id rejection:** `emit` for a `workflow_id` with no live `wf_registry` row (§5.10.2) is **rejected** and creates **no** cache row. `wf_event_cache` additionally enforces a global cardinality cap with oldest-past-horizon eviction.
+- **emit rate:** an optional per-role/per-workflow emit rate limit (configurable) bounds cache growth even for legitimate-id floods.
+
+These caps are documented defaults and part of the install-time consistency validation (§5.7.2).
+
+### 5.13 Constraints honored
+
+Reduces cleanly to `insert_event`, `next_batch` (with its `max_events` bound, §5.9 #4), `get_batch_events`, `finish_batch`, `event_retry` (+ `send_at`) plus the small side tables of §5.5 (including the single-row-per-consumer `wf_dispatch_control`). Single-file, no C extension, no `shared_preload_libraries`, no restart; managed-PG compatible. **pg_cron is optional for always-on-dispatcher topologies but REQUIRED for scale-to-zero/serverless timeout liveness (§5.7.1).** PostgreSQL 14–18; **minimum PgQ engine version/feature floor gated at install (§5.9).** `pg_snapshot`/`xid8`; `pgcrypto` for capability generation. All SECURITY DEFINER functions pin `search_path = pgque, pg_catalog` and are `REVOKE`d from `PUBLIC` (§5.10). No subtransactions in hot paths. The await/emit serialization (§5.7.3) and the join-completion serialization (§5.8) both use transaction-scoped advisory/row locks only — no claim/lease model; the consumer-wide `wf_dispatch_control` row (§5.2) is a single HOT-updated coordination row, not a per-workflow lease. Ships as optional experimental `sql/experimental/durable.sql` gated by the promotion rule.
+
+### 5.14 Observability / monitoring (if state is in the message, how do we monitor?)
+
+Monitoring does **not** require a per-step-mutated status row. Four layers, three of them free/cheap and bloat-free:
+
+1. **Parked workflows — free.** `awaitEvent`/`sleep`/`awaitAll` each already have a coordination row (`wf_wait`, `wf_join`, scheduled `send_at`). "What's waiting, on what, for how long, what's overdue/stuck" is a `SELECT` over those small tables — at coordination-point rate, not transition rate.
+2. **Live in-flight workflows — indexed lookup over the rotating queue.** `workflow_id` rides in `ev_extra1` and `step_seq`/`step_name` in `ev_extra2/3` (existing PgQ event columns). **Index `ev_extra1`** so `WHERE ev_extra1 = :workflow_id` and "list everything running now" are indexed queries directly on the event tables. The index rotates with the tables (TRUNCATE-reclaimed → zero bloat) and only ever holds the in-flight window (bounded by concurrency). Cost: one extra index on the insert path (modest, optional). No separate mutable status row.
+3. **Aggregate & historical — append-only audit stream, exported.** Throughput, success/failure rates, latency, per-step timing, and counts-in-last-hour come from `wf_audit` (append-only, rotating, §5.10.3), **exported to OTel/Prometheus/ClickHouse before rotation** — the mature-systems pattern (emit an event stream to a column store), not querying the hot OLTP table. Reuse PgQue's existing `get_queue_info` / `queue_health` / OTel surface; add a "workflows overview" view (counts by state) and DLQ inspection (reuses existing DLQ).
+4. **Convenient dashboard / exact per-step liveness — opt-in `wf_live` (§5.5).** Default granularity = park/start/terminal boundaries (coordination-rate; gives running | waiting-on-X | sleeping-until-T | done | failed with no per-step churn). Opt-in high-resolution = updated every step (exact current step, at the documented per-step `UPDATE` cost — HOT-optimized, one row/workflow). The user chooses the bloat/observability trade.
+
+**Honest trade.** Everything except **exact per-step liveness of a still-running workflow** is free or cheap and bloat-free. That one thing is the only opt-in that costs per-step writes. vs DBOS: they give `SELECT current_step` for free because they already pay the per-step write (and its bloat); we give parked-state + running-set + full historical metrics for free/cheap and make exact per-step liveness the single opt-in knob.
+
+---
+
+## 6. Tests plan
+
+### 6.1 Hard repo rule
+
+**Red/green TDD for ALL new code.** Every function below is written test-first: a failing test asserting the behavior, then the implementation that makes it pass. CI rejects any new SQL function or SDK method without a preceding failing-then-passing test in the same change.
+
+### 6.2 Built test-first, in this order (highest risk first)
+
+1. **Exactly-once handoff** (§5.1) — kill the txn between `insert_event` and `commit`, assert no successor + clean redelivery; assert no double-handoff on commit.
+2. **Per-step idempotency + dedup-horizon + delivery-anchor clock** (§5.4/§5.4.1) — deliver the same `(workflow_id, step_seq)` twice → exactly one successor + one side effect; redeliver at horizon-boundary age → routed to DLQ, no double-handoff; **the mandatory positive test: a `sleep` longer than `dedup_horizon` resumes normally and is NOT DLQ'd**; **AND the staleness-gate ordering test: the §5.4.1 staleness check runs and commits its DLQ route BEFORE any user body executes, and a stale event is never handed to a body that aborts** (guards the §5.4.1↔§5.2 reconciliation).
+3. **Transaction-boundary / retry resolution** (§5.2) — a retry continuation re-enqueues via `send_at` with a **fresh `step_seq`** and, on delivery, **re-executes its body** (assert the step logic runs once per retry attempt up to `max_retries`, then lands in DLQ); an unexpected exception aborts only a bounded batch; **single-dispatcher poison-pill isolation: a poison event sharing a starting batch of size K with several innocent co-tenant workflows is quarantined to the DLQ via consumer-wide `max_events`-reduction-to-1, and every innocent co-tenant ultimately commits and is NOT DLQ'd**; **AND the multi-subconsumer redelivery test: with ≥2 cooperative subconsumers running, an aborting poison event is redelivered to a DIFFERENT subconsumer than the one that aborted, and the consumer-wide `wf_dispatch_control` reduction ensures that other subconsumer also requests size-1 batches — assert the poison is NOT re-aggregated with innocents at `max_events=K` and no innocent co-tenant is forced to the DLQ** (guards the subconsumer-safety fix; exercises engine contract #4 across subconsumers); **AND the quarantine up-ramp test: after `quarantine_cooldown` clean size-1 commits, `current_max_events` is restored to K**.
+4. **`awaitEvent` / `emit` race matrix** (§5.7) — one test per row; `cache_retention_horizon` never drops a within-horizon entry and is **independent of `await_timeout`** (a long await behind a fast emit is not rejected, §5.7.2); advisory-lock serialization correct under simulated transaction-pooling, including a **hash-collision correctness-safety** test (§5.7.3); single-resume token proven by concurrent emit+sweep.
+5. **fan-out / join** (§5.8) — race-free join-total recording; idempotent completed-set under duplicated completion; **exactly-once parent resume proven with CONCURRENT FINAL COMPLETERS — assert the parent IS resumed exactly once (not zero, not twice), exercising the per-join completion lock at READ COMMITTED**; **per-child result array assembled from `wf_join_done` (spill) with a resume payload under `max_payload_bytes` at full `max_spawn_fanout`**; spawn-fanout cap enforced.
+6. **Authorization & capability** (§5.10/§5.11) — PUBLIC cannot execute any durable function; `emit` without the `workflow_id` capability fails; `emit` for an id absent from `wf_registry` is rejected with no cache row; an approval-class `emit` without the mandatory per-wait token fails even with a valid id; forged-approval with a guessed sequential id fails; **`workflow_id` column is defaulted by `gen_random_uuid()`/`pgcrypto` and CI statically rejects any sequence/serial-derived id path**; `wf_audit`/DLQ store hashed ids; audit row with `actor_id` written for every emit/resume/spawn.
+7. **Observability surface** (§5.14) — parked-workflow view returns correct waiting/sleeping/overdue sets; `ev_extra1`-indexed running-set query returns the in-flight window; `wf_audit`-derived metrics view returns correct counts; `wf_live` boundary-granularity reflects start/park/terminal with no per-step write, and high-resolution opt-in reflects exact current step (asserting the per-step `UPDATE` happens only in high-res mode).
+
+### 6.3 CI test suites
+
+- **Unit (pgTAP/SQL):** each durable function; coordination-table invariants (incl. `wf_dispatch_control` single-row-per-consumer + `wf_live` one-row-per-live-workflow model); `search_path` pinning; **grant-audit** (no PUBLIC execute); "no subtransaction in hot path" lint; resource-cap enforcement (fanout, payload, cache cardinality, emit rate).
+- **Engine-contract regression tests** (§5.9): tick-visibility ordering; **durable per-event retry-count + DLQ routing**; `send_at` delayed-delivery behavior; **`next_batch` honors the caller-supplied `max_events` bound down to 1, and unfinished events of an aborted batch are redelivered subject to that bound to whichever subconsumer next calls** (contract #4). Each fails loudly if engine behavior regresses, plus an **install-time engine-floor gate** test covering all four contracts.
+- **Concurrency/property tests:** randomized interleavings of emit/await/timeout and spawn/complete under multiple subconsumers; exactly-once resume + no orphaned waits/joins/registry rows; **concurrent-final-completer join liveness (no lost resume)**; **multi-subconsumer poison-isolation (no re-aggregation via the shared `wf_dispatch_control` bound)**.
+- **Crash/idle-recovery tests:** worker death mid-batch → `dead_interval` takeover + single redelivery + idempotent no-op; **timeout liveness with a running dispatcher and pg_cron disabled** (§5.7.1); **and a scale-to-zero test asserting timeouts fire via pg_cron when no dispatcher is running.**
+- **Matrix:** PostgreSQL 14, 15, 16, 17, 18.
+- **Engine-sacredness guard:** CI diff-check that no file under the PgQ engine path is modified by this change.
+
+### 6.4 Manual acceptance (maps 1:1 to §3 user stories)
+
+Each of the six user stories has a runnable scenario script the reviewer executes by hand against a managed-PG-like instance, including the §3.3 forged-approval negative check (with and without the per-wait token), the §3.2 long-sleep-resumes-not-DLQ'd check, the §3.4 concurrent-completer exactly-once-resume check, and the §3.6 observability walkthrough.
+
+### 6.5 Success-criterion benchmark (the entire pitch) — gated, NOT a per-change CI suite
+
+Throughput-and-bloat benchmark vs a mutable-status-row baseline (DBOS/absurd shape) on server hardware. Publishes, over a long sustained run: **`n_dead_tup`** (flat for the PgQue await-light hot path; rising for baseline), **sustained transitions/sec** (targeting tens of thousands per database for await-light, flat under sustained load, §1/§5.6.1), the **coordination-table dead-tuple curve**, and an explicit **await/join-heavy A/B workload** that coordinates on (nearly) every step, so the §5.6 scoped headline is substantiated rather than asserted. Because long VACUUM-wall runs are slow and noisy, this is a **nightly / on-demand gated harness**, explicitly out of the per-change CI gate (which runs only a short smoke version). The full harness is reproducible and versioned.
+
+---
+
+## 7. Team (veteran experts to hire)
+
+- **Veteran PostgreSQL internals / MVCC engineer (1)** — snapshot/visibility reasoning, `xid8`/`pg_snapshot`, rotation interaction, no-subtransaction guarantee, engine-contract tests (§5.9 incl. the `next_batch` max-events bound and its cross-subconsumer redelivery semantics), engine-floor install gate.
+- **Veteran durable-execution / distributed-systems engineer (1)** — await/emit and fan-out/join race designs, single-resume-token proofs, the join-completion serialization + lost-resume closure (§5.8), the dedup-horizon + delivery-anchor bound (§5.4.1), the transaction-boundary/retry resolution incl. retry-`step_seq` semantics and the consumer-wide `wf_dispatch_control` poison-pill `max_events` size-1 isolation + up-ramp recovery (§5.2).
+- **Veteran PostgreSQL security engineer (0.5, shared)** — authorization model (§5.10), capability generation + confidentiality/leakage model (§5.11), mandatory per-wait token, audit attribution under pooling, grant-audit tests, resource caps (§5.12).
+- **Veteran PL/pgSQL + SQL test engineer (pgTAP) (1)** — red/green TDD harness, concurrency/property tests (incl. concurrent-completer join liveness AND multi-subconsumer poison-isolation), crash-recovery + pg_cron-disabled and scale-to-zero liveness injection, the positive long-sleep-not-DLQ'd, staleness-gate-ordering, retry-re-execution, and quarantine up-ramp tests.
+- **Veteran SDK / developer-experience engineer (Python) (1)** — the one reference SDK and the thin-client surface, incl. `awaitAll` result-array assembly from the spill table; the SDK side of the observability surface.
+- **Veteran observability / SRE engineer (0.5, shared)** — the §5.14 views, `ev_extra1` index, `wf_audit`→OTel/Prometheus/ClickHouse export pipeline, workflows-overview + DLQ inspection.
+- **Veteran performance / benchmarking engineer (1)** — the gated throughput-and-bloat benchmark incl. the await/join-heavy A/B and the published curves.
+- **Veteran technical writer / DX reviewer (0.5, shared)** — experimental-feature docs, honest-claim framing (§5.6), ops/authz guide (required pg_cron-for-scale-to-zero, autovacuum settings, capability-leakage hygiene).
+
+### 7.1 Persona for this spec round
+
+Veteran **"Durable Workflow Engineer"** (accepted).
+
+---
+
+## 8. Implementation plan (sprints, parallelization, ordering)
+
+**Sprint 0 — Foundations & harness (1 wk).**
+- Test engineer: pgTAP red/green harness, CI matrix (PG 14–18), engine-sacredness diff-guard, grant-audit scaffold. *(blocks everyone.)*
+- PG-internals engineer: spike the primitive reduction; confirm `send_at` (PR #237), the durable per-event retry counter, **and the `next_batch` max-events bound incl. cross-subconsumer redelivery (contract #4)**; draft the engine-contract tests + install-time engine-floor gate (§5.9).
+- Security engineer: role model + `REVOKE`-from-PUBLIC install template + capability generation and leakage-hygiene defaults (§5.11).
+- *Parallel:* SDK engineer scaffolds the thin Python client against stub SQL signatures.
+
+**Sprint 1 — Exactly-once core (1.5 wk).** *(highest risk first)*
+- PG-internals + distributed-systems engineers (pair): exactly-once handoff (§5.1); per-step idempotency + dedup-horizon/delivery-anchor + staleness-gate ordering (§5.4/§5.4.1, incl. the positive long-sleep test); transaction-boundary/retry resolution with retry-`step_seq` semantics and the consumer-wide `wf_dispatch_control` poison-pill size-1 isolation + up-ramp (§5.2).
+- Test engineer: crash-recovery + `dead_interval` takeover; single-dispatcher AND multi-subconsumer poison-isolation tests; retry-re-execution test; quarantine up-ramp test.
+- *Gate:* no further work merges until §5.1/§5.2/§5.4 tests are green.
+
+**Sprint 2 — Coordination primitives (2 wk).** *Two parallel tracks:*
+- **Track A** (distributed-systems): `awaitEvent`/`emit` race matrix (§5.7) — wait registry, first-write-wins cache with separated `cache_retention_horizon` (§5.7.2), advisory-xact-lock serialization (§5.7.3), single-resume token, in-loop timeout sweep + scale-to-zero pg_cron path (§5.7.1).
+- **Track B** (PG-internals): fan-out/join (§5.8) — join-total atomicity against the engine contract (§5.9), idempotent completed-set, **per-join completion serialization + lost-resume closure**, result spill to `wf_join_done`, exactly-once parent resume, spawn cap.
+- Security engineer (parallel): `wf_registry` + emit authz/liveness, mandatory per-wait token, audit with `actor_id` + hashed ids (§5.10).
+- Test engineer rotates across tracks writing red tests ahead of each piece, incl. the concurrent-completer join-liveness and multi-subconsumer poison tests.
+
+**Sprint 3 — SDK + dispatch + caps + observability (1.5 wk).**
+- SDK engineer: finalize `defineWorkflow/step/sleep/awaitEvent/emit/spawn/awaitAll` over the stable SQL, incl. result-array assembly.
+- PG-internals engineer: dispatch loop (§5.2) incl. in-loop sweep + consumer-wide `wf_dispatch_control` `max_events`-reduction poison isolation + up-ramp, `sleep` via rotating `send_at`, resource caps (§5.12), optional `wf_live` projection (one-row-per-live-workflow HOT-update model, §5.5).
+- Observability/SRE engineer: §5.14 views, `ev_extra1` index, `wf_audit`→OTel/Prometheus/ClickHouse export.
+- *Parallel:* benchmarking engineer builds the baseline (DBOS/absurd-shape) rig + the await/join-heavy A/B harness.
+
+**Sprint 4 — Benchmark, hardening, docs (1.5 wk).**
+- Benchmarking engineer: run the gated benchmark (§6.5); publish all curves incl. await/join-heavy A/B.
+- Whole team: concurrency/property hardening, `search_path` + grant audit, no-subtransaction lint, pg_cron-disabled + scale-to-zero liveness tests.
+- Writer: experimental docs incl. honest-claim framing (§5.6), required pg_cron-for-scale-to-zero, autovacuum settings, capability-leakage hygiene, audit export, observability guide; promotion checklist.
+
+**Critical path:** Sprint 0 harness → Sprint 1 exactly-once gate → Sprint 2 Track A & B (parallel) → Sprint 3 → Sprint 4 benchmark. SDK, security, observability, and benchmark-rig work parallelize off the critical path.
+
+---
+
+## 9. Topic-specific: API surface (reference SDK, Python v0.1)
+
+```python
+wf = defineWorkflow("order_fulfillment")
+
+@wf.step("charge")
+def charge(ctx, state):
+    ctx.side_effect(...)              # user's own idempotent/in-txn write
+    return ctx.goto("await_ship", state)        # append successor
+
+@wf.step("await_ship")
+def await_ship(ctx, state):
+    return ctx.await_event("shipped", timeout="24h",
+                           on_event="notify", on_timeout="escalate",
+                           require_token=True)   # mandatory token for approval-class
+
+@wf.step("fan")
+def fan(ctx, state):
+    return ctx.spawn([...N children...], join="collect")   # N ≤ max_spawn_fanout
+
+@wf.step("collect")
+def collect(ctx, state):
+    results = ctx.join_results()      # assembled from wf_join_done spill (§5.8)
+    ...
+
+# authorized external producer (role: pgque_durable_client), holding the capability + wait token:
+emit(workflow_id, "shipped", payload, token=wait_token, actor_id="svc:shipping")
+```
+
+Every SDK call compiles to one of the PgQ primitives + a coordination-table touch, subject to the authorization (§5.10) and resource (§5.12) checks. The programming model is a message-driven **state machine** (think AWS Step Functions / actors). **One reference client (Python) in v0.1; other-language clients (Go/TS/WIP) are a deferred follow-up** (§11/§12) — cheap to add later precisely because durability lives in SQL and each client is a thin wrapper, kept aligned by a shared cross-client conformance suite. **No** `async/await`-compiled linear-code DX in v0.1 (deferred, §12).
+
+---
+
+## 10. Operability notes (managed-PG)
+
+- **pg_cron — required for scale-to-zero (§5.7.1).** For always-on-dispatcher topologies it is an optimization; for serverless / scale-to-zero, pg_cron driving `run_timeout_sweep()` is a **correctness requirement** for timeout liveness. The install script warns if neither a long-running dispatcher nor pg_cron is configured.
+- **Engine floor (§5.9/§5.13):** install gates on the minimum PgQ engine version — `send_at` present, durable per-event retry counter exposed, tick-visibility per contract, `next_batch` honoring the `max_events` bound (incl. cross-subconsumer redelivery) — and fails loudly otherwise.
+- **Poison-pill quarantine is consumer-wide (§5.2).** Operators should know that a persistently-aborting (poison) event transiently collapses the *entire logical consumer* to size-1 batches until the event is DLQ'd and `quarantine_cooldown` clean commits restore throughput — a brief, self-healing throughput dip, not a per-process anomaly. `quarantine_cooldown` and starting `K` are documented tunables.
+- **Required operator settings:** documented autovacuum tuning for the `DELETE`-driven coordination tables (`wf_registry`, `wf_wait`, `wf_join`) and for `wf_live` if enabled (HOT-update churn at its configured granularity, §5.5) so their dead-tuple rate (§5.6) stays bounded; rotation cadence for `wf_dedup`/`wf_event_cache`/`wf_audit`. The await/join-heavy dead-tuple characterization (§5.6) is documented so operators size autovacuum for their workload shape.
+- **Observability (§5.14):** enable the optional `ev_extra1` index for the running-set view; wire the `wf_audit` export to OTel/Prometheus/ClickHouse; choose `wf_live` granularity (boundary default vs per-step opt-in) per the bloat/visibility trade.
+- **Capability-leakage hygiene (§5.11):** disable statement-parameter logging for the durable schema; `workflow_id` is stored hashed in `wf_audit` and DLQ; treat the id as a secret and prefer the mandatory per-wait token for approvals.
+- **Audit export (§5.10.3):** the `wf_audit` rotating table must be exported to durable storage before rotation; export hook + retention policy are part of the docs. Honest limitation: the log is append-only-by-convention, not cryptographically tamper-evident (hash-chaining deferred, §11).
+- **Install-time validation:** validates mutual consistency of `dedup_horizon`, `cache_retention_horizon`, `await_timeout` ceiling, `dead_interval`, `max_retry_backoff`/`max_batch_duration`, `quarantine_cooldown`/starting `K`, and the resource caps, and fails loudly on inconsistency.
+
+---
+
+## 11. Open items carried to v0.6
+
+- Quantitative defaults for every configured bound (`dedup_horizon`, `cache_retention_horizon`, `max_spawn_fanout`, `max_payload_bytes`, emit rate, starting batch `K`, `quarantine_cooldown`) validated against the benchmark.
+- Per-wait emit-token issuance/rotation/revocation detail (§5.10.2) — now mandatory for approval-class, but the token lifecycle is still to be fully specified.
+- **Audit hash-chaining / signing** for genuine tamper-evidence (§5.10.3) — deferred enhancement beyond append-only-by-convention.
+- **A verification pass on the v0.5 fix-induced redesigns before promotion** — specifically: the consumer-wide `wf_dispatch_control` poison-pill isolation + up-ramp recovery across subconsumers (§5.2, new table, new multi-subconsumer test) and its interaction with engine contract #4's cross-subconsumer redelivery (§5.9); the unified `wf_live` one-row-per-live-workflow HOT-update model (§5.5); and the §5.4.1↔§5.2 staleness-gate-ordering / dual-DLQ-route reconciliation. These want independent confirmation — including whether a single shared `wf_dispatch_control` row becomes a write-contention point under many subconsumers + frequent aborts (expected rare, but unmeasured).
+- Other-language clients (Go, TypeScript, + WIP) as thin SQL wrappers + the shared cross-client conformance suite — deferred follow-up after the Python reference client (§9/§12).
+- Cancellation / orphan-join propagation remains deferred (§12).
+
+---
+
+## 12. Non-goals / disclaimers (honored strictly — not reintroduced anywhere above)
+
+- **Mechanism distinction (NOT a competitive disclaimer).** PgQue Durable Workflows is a direct, better, no-new-infra, stays-fast **alternative to Temporal and DBOS** — it competes with them and delivers the same core durable-execution guarantees (§1). It deliberately does **not** reproduce their *durability mechanism*: deterministic replay of a long-lived linear function backed by a `workflow_status` row mutated on every step. That mechanism is precisely the source of the per-step `UPDATE` bloat we exist to eliminate. **Eliminating per-step `UPDATE` churn is a goal/benefit (§1), never a non-goal.** What we disclaim is only the *technique*: no determinism requirement imposed on user code, and no replay-of-a-linear-function programming model in v0.1 (a continuation-compiling SDK is deferred).
+- **NOT** a per-language deterministic-replay *runtime* like Temporal's heavy per-language engines. Workflow support is intended to ship across all PgQue clients eventually as **thin SQL wrappers** (the architecture makes that cheap), but **v0.1 ships one reference client — Python**; Go/TypeScript/WIP are a deferred follow-up (§9/§11), not part of the v0.1 scope or team.
+- **NOT** a separate server, daemon, or external datastore. No Cassandra, RocksDB, FoundationDB, or Redis.
+- **Throughput is NOT conceded to a low ceiling.** Target: **tens of thousands of simple (await-light) transitions/sec per database, flat under sustained load** (higher with batching); coordination-heavy transitions cost more and are characterized honestly (§5.6); scale beyond a single node by sharding workflows across databases — that is scale-out, not an apology. The single-workflow sequential rate is ~tick-rate and is stated plainly (§5.6.1) so the aggregate claim is not misread.
+- **NOT** changing the sacred PgQ engine, and **NOT** introducing a second `SELECT … FOR UPDATE SKIP LOCKED` claim/lease concurrency model as the primary mechanism — exclusivity comes from the single-live-continuation invariant over the existing rotation engine. (The transaction-scoped advisory lock of §5.7.3, the per-join `SELECT … FOR UPDATE`/advisory lock of §5.8, and the single per-consumer `wf_dispatch_control` row of §5.2 are coordination-table serialization/control primitives, **not** a workflow-claim/lease mechanism.)
+- **Cancellation / orphan-join propagation is deferred** to a follow-up, not in v0.1.
+- Linear-code (`async/await`-compiled) DX is an explicit **later** SDK project, not an engine requirement.
+
+---
+
+## 13. Embedded Changelog
+
+- **v0.5** (2026-05-30) — Closed the two blocking findings + three minors Reviewer B raised against v0.4 (Reviewer A unavailable this round), and re-aligned the user-facing framing to the idea's hard rules. **GENUINELY populated the §4 canonical architecture block** with the layered SDK→durable-layer→sacred-engine diagram inside the `architecture:begin/end` markers — correcting a twice-repeated regression where the v0.3 and v0.4 changelogs each falsely claimed the block was filled while the literal "(architecture not yet specified)" placeholder remained; this entry's claim is verifiable against §4 as written (the prior false v0.4 claim is corrected in the v0.4 entry below). **Made the poison-pill isolation subconsumer-safe**: the v0.4 `max_events`-reduction-to-1 was process-local dispatcher state, so under the mandated cooperative *subconsumers* (§4.3) a redelivered poison event could be re-aggregated with innocents by a subconsumer still at `max_events=K`; v0.5 moves the bound into a new **consumer-wide `wf_dispatch_control` row** (one row per logical consumer, written in a separate committed txn that survives the abort, read by every subconsumer before each `next_batch`) so the reduction is uniform across all subconsumers, and added a **multi-subconsumer redelivery test** (§6.2 item 3, §6.3) plus the cross-subconsumer redelivery clause to engine contract #4 (§5.9). **Specified the `max_events` up-ramp/recovery policy** (§5.2): restore to `K` after `quarantine_cooldown` consecutive clean size-1 commits (count-gated, not time-gated). **Unified the `wf_live` model** (§4.2/§5.5/§5.6): withdrew the inconsistent "append-based, rotating, not insert+delete" description and pinned it as a **one-row-per-live-workflow HOT-`UPDATE`d projection**. **Reconciled the two DLQ-routing mechanisms and pinned ordering** (§5.4.1/§5.2): the staleness gate is a pre-body, route-not-process check that commits cleanly before any user body runs; the engine retry counter (contract #2) is the abort-channel route after a body has run and aborted. **Re-led with user outcomes** per the idea's hard framing rule: §1 Goal/positioning rewritten in stays-fast/no-new-infra/crash-proof outcome language with the event-sourcing mechanism demoted to a "How it works" subsection; **restored the idea's ambitious throughput target** (tens of thousands of await-light transitions/sec per database, scale-out by sharding) and **removed the "a few thousand / conceded to Temporal" framing** the idea explicitly forbids; **added the make-or-break per-transition-UPDATE rebuttal as a dedicated subsection** (§5.1.1); **added the honest single-workflow latency characterization** (§5.6.1); **added the mandated Observability section** (§5.14) with a sixth on-call user story (§3.6), observability tests (§6.2 item 7), and an observability/SRE half-hire (§7). Updated team/plan/tests/open-items/ops accordingly. All five Reviewer B findings accepted.
+- **v0.4** (2026-05-30) — Closed all seven findings Reviewer B raised against v0.3 (Reviewer A unavailable this round). **NOTE (corrected in v0.5): this entry originally claimed the §4 architecture diagram was "actually populated" — that claim was false; the literal "(architecture not yet specified)" placeholder in fact remained, repeating the identical false claim the v0.3 entry made. The block was genuinely filled only in v0.5.** Corrected throughput positioning to the (later-reverted) "a few thousand transitions/sec" framing; **v0.5 reverts this back to the idea's ambitious target.** Redesigned poison-pill containment to use **only the existing `next_batch` `max_events` bound (reduce to size 1)** for isolation, withdrawing the v0.3 "re-process the same snapshot range with the batch split" framing; added the `next_batch` max-events bound as **explicit engine contract #4** (§5.9). **(Defect found in v0.5 review: the v0.4 reduction was process-local and not subconsumer-safe — fixed in v0.5 via `wf_dispatch_control`.)** Closed the fan-out/join **lost-resume race**: completion counting now serializes on the `wf_join` row (`SELECT … FOR UPDATE` / per-join advisory lock) at **READ COMMITTED**, and added a concurrent-final-completer liveness test (§5.8/§6.2/§6.3). Removed the undefined "within-horizon pre-registration" emit-authz clause as redundant. Reduced the client-scope claim to the **one Python reference client** actually staffed. Updated team, plan, tests, open items accordingly. All seven Reviewer B findings accepted.
+- **v0.3** (2026-05-30) — Closed the fix-induced contradictions both reviewers raised against v0.2. Redefined dedup-horizon enforcement around a per-transition `delivery_anchor` so long `send_at` sleeps are never misclassified as stale redeliveries and DLQ'd, and recomputed the bound as single-attempt (§5.4.1). Pinned retry continuations to a fresh `step_seq` so they re-execute instead of being swallowed as a dedup no-op (§5.2/§5.4). Redesigned poison-pill containment onto the engine's durable per-event retry counter (§5.2), pinned as an explicit engine contract (§5.9). Replaced the unbounded per-key lock row with a transaction-scoped advisory lock (§5.7.3). Separated `cache_retention_horizon` from `await_timeout` (§5.7.2). Spilled per-child join results to `wf_join_done` (§5.8). Made timeout liveness an explicit operator invariant — pg_cron REQUIRED for scale-to-zero (§5.7.1, §10). Introduced a mandatory `wf_registry` as the authoritative emit-liveness source (§5.5/§5.10.2/§5.12). Added a `workflow_id` confidentiality/leakage model (§5.11). Corrected the audit overclaim and added `actor_id` attribution (§5.10.3). Scoped the flat-dead-tuple headline to await-light loops (§5.6/§6.5). Stated a minimum PgQ engine floor (§5.9/§5.13). Attempted to fill the empty §4 architecture block (placeholder in fact remained — corrected in v0.5). All findings from both reviewers accepted.
+- **v0.2** (2026-05-30) — Hardening round against Reviewer A (security/ops). Added authorization model (§5.10) and `workflow_id`-as-unforgeable-capability (§5.11). Stated the dedup-horizon bound and its DLQ enforcement (§5.4.1). Resolved the batch-transaction vs per-event-retry contradiction (§5.2). Made timeout liveness a non-optional property of the dispatch loop (§5.7.1). Pinned the await/emit lock to a pooler-safe transaction-scoped lock (§5.7.3). Bounded `wf_event_cache` retention (§5.7.2). Demoted `wf_live` to optional/opt-in (§5.5). Refined the zero-bloat claim (§5.6). Added resource caps (§5.12). Stated the engine tick-visibility coupling as a regression-tested contract (§5.9). Scoped the benchmark out of per-change CI (§6.5). Added security engineer, operability section (§10), open-items (§11). Reviewer B unavailable this round.
+- **v0.1** (2026-05-30) — Initial spec scaffold fleshed into full structure. Resolved all five delegated interview questions. Added Goal-&-why framing, user stories, layered architecture with the sacred-engine boundary, hot-path/coordination detail incl. the honest zero-bloat correction, await/emit + fan-out/join race designs, red/green TDD-first ordering, team roster, 5-sprint plan, SDK surface, and strict non-goals. No reviewer findings yet (first authoring round).
diff --git a/blueprints/workflows/TLDR.md b/blueprints/workflows/TLDR.md
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+++ b/blueprints/workflows/TLDR.md
@@ -0,0 +1,25 @@
+# TL;DR
+
+## Goal
+
+> Status: **experimental**, ships as optional `sql/experimental/durable.sql` gated by the project promotion rule. Workflow support ships first as **one thin-SQL-wrapper reference client (Python)**; the other PgQue clients (Go, TypeScript, + WIP) are a planned follow-up, not v0.1 (§7–§9, §12). Engine layer is sacred and untouched.
+
+## Scope summary
+
+- 1. Goal & why it's needed
+- 2. Scope & resolved interview decisions
+- 3. User stories
+- 4. Architecture
+- 5. Implementation details
+- 6. Tests plan
+- 7. Team (veteran experts to hire)
+- 8. Implementation plan (sprints, parallelization, ordering)
+- 9. Topic-specific: API surface (reference SDK, Python v0.1)
+- 10. Operability notes (managed-PG)
+- 11. Open items carried to v0.6
+- 12. Non-goals / disclaimers (honored strictly — not reintroduced anywhere above)
+- 13. Embedded Changelog
+
+## Next action
+
+`already published as v0.1`
diff --git a/blueprints/workflows/architecture.json b/blueprints/workflows/architecture.json
new file mode 100644
index 00000000..f46cd630
--- /dev/null
+++ b/blueprints/workflows/architecture.json
@@ -0,0 +1,5 @@
+{
+  "version": "1",
+  "nodes": [],
+  "edges": []
+}
diff --git a/blueprints/workflows/changelog.md b/blueprints/workflows/changelog.md
new file mode 100644
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--- /dev/null
+++ b/blueprints/workflows/changelog.md
@@ -0,0 +1,28 @@
+# changelog
+
+## v0.1 — 2026-05-30T09:34:38.223Z
+
+- Initial draft authored by the lead.
+- Persona: Veteran "Durable Workflow Engineer" expert
+## v0.2 — 2026-05-30T09:43:28.231Z
+
+- Round 1 reviews applied (decisions — accepted: 13, rejected: 0, deferred: 0).
+
+- user-edit before round 2
+## v0.3 — 2026-05-30T09:55:00.614Z
+
+- Round 2 reviews applied (decisions — accepted: 20, rejected: 0, deferred: 0).
+
+- user-edit before round 3
+
+- user-edit before round 3
+
+- user-edit before round 3
+## v0.4 — 2026-05-30T11:37:14.368Z
+
+- Round 3 reviews applied (decisions — accepted: 7, rejected: 0, deferred: 0).
+
+- user-edit before round 4
+## v0.5 — 2026-05-30T11:56:01.783Z
+
+- Round 4 reviews applied (decisions — accepted: 5, rejected: 0, deferred: 0).
diff --git a/blueprints/workflows/decisions.md b/blueprints/workflows/decisions.md
new file mode 100644
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--- /dev/null
+++ b/blueprints/workflows/decisions.md
@@ -0,0 +1,60 @@
+# decisions
+
+- No review-loop decisions yet.
+
+## Round 1 — 2026-05-30T09:43:28.231Z
+
+- accepted missing-risk#1: Added §5.10 authorization model — REVOKE EXECUTE FROM PUBLIC on all durable functions, dedicated worker/client roles, and caller-scoped emit authorization — closing the privilege-escalation path on the approval flow.
+- accepted missing-risk#2: Added §5.11 requiring workflow_id to be a 128-bit CSPRNG-generated unforgeable capability, with a test rejecting predictable id generation, so coordination primitives cannot be driven by id enumeration.
+- accepted weak-implementation#1: Added §5.4.1 stating the explicit dedup_horizon ≥ max-redelivery-latency bound and enforcing it by routing over-horizon events to DLQ rather than reprocessing, preventing marker-rotation double-handoff.
+- accepted weak-implementation#2: Resolved in §5.2: the batch is the single transaction unit, transient retries become returned send_at continuations (subtransaction-free appends), unexpected exceptions abort only a size-bounded batch, and repeat offenders are quarantined to DLQ to cap poison-pill amplification.
+- accepted missing-risk#3: Added §5.7.1 making the timeout sweep a hard property of the dispatch loop itself (run every iteration including idle tick-sleeps), so timeout liveness no longer depends on optional pg_cron; asserted by a pg_cron-disabled test.
+- accepted weak-implementation#3: Pinned §5.7.3 to a transaction-scoped row lock via INSERT…ON CONFLICT + SELECT…FOR UPDATE on the exact (workflow_id,event_name) key, pooler-safe under PgBouncer and collision-free, and explicitly forbade session-level advisory locks.
+- accepted missing-risk#4: Added §5.7.2 retaining cache entries for a configured await horizon guaranteed ≥ worst-case await latency, GC evicting only past-horizon entries and rejecting awaits whose deadline exceeds the horizon, eliminating silent loss of a legitimate emit-before-await.
+- accepted unnecessary-scope#1: Demoted wf_live to an optional, opt-in, default-OFF, append-based/rotating projection that is never required for correctness (addressing remains by workflow_id in user tables), removing the insert+delete per-workflow dead-tuple tax on the headline property.
+- accepted weak-implementation#4: Rewrote §5.6 to separate concurrency-bounded live row-count from coordination-throughput-bounded cumulative dead-tuple rate, conceding DELETE-driven tables need autovacuum/rotation and publishing their dead-tuple curve in the benchmark.
+- accepted missing-risk#5: Added §5.12 caps: max_spawn_fanout, hard max_payload_bytes, unknown-id emit rejection with no cache row, cache cardinality cap, and optional emit rate limit, closing the bloat/DoS vectors on the externally driven surfaces.
+- accepted weak-implementation#5: Added §5.9 stating the tick-visibility dependency as an explicit engine contract with a regression test that fails if engine tick/visibility semantics change, converting a silent join-correctness break into a CI failure.
+- accepted missing-risk#6: Added §5.10.3 wf_audit, an append-only rotating table recording role-attributed emit/resume/spawn/timeout actions exported before rotation, providing a tamper-evident trail for approval/escalation flows.
+- accepted unnecessary-scope#2: Scoped the heavy sustained throughput-and-bloat benchmark out of the per-change CI gate to a nightly/on-demand gated harness (§6.5), keeping only a short smoke version in standard CI.
+
+## Round 2 — 2026-05-30T09:55:00.614Z
+
+- accepted rA-1: Resolved by defining a per-transition delivery_anchor (reset at timer fire) as the horizon clock and recomputing the bound to single-attempt, so a woken 7-day sleep has ~0 redelivery age and is never DLQ'd (§5.4.1).
+- accepted rA-2: Rebuilt poison-pill containment on PgQ's durable per-event retry counter (pinned as engine contract §5.9) plus a dispatcher fault-isolation re-dispatch that halves the batch to isolate the offender — removing the un-writable side-table counter and the per-workflow-selection assumption (§5.2).
+- accepted rA-3: Surfaced the no-running-dispatcher gap explicitly and made pg_cron a hard correctness requirement for scale-to-zero/serverless topologies, with an install warning and a dedicated test (§5.7.1, §10, §6.3).
+- accepted rA-4: Eliminated the never-reclaimed lock row entirely by switching to a transaction-scoped advisory lock (no row, pooler-safe, hash-collision-correctness-safe), so the locking primitive contributes zero tuples (§5.7.3, §5.5).
+- accepted rA-5: Spilled per-child results into wf_join_done and reduced the parent resume payload to a join reference, so a full 1024-child fan-out stays under the 8 KiB payload cap (§5.8).
+- accepted rA-6: Dropped the 'tamper-evident' claim (deferred hash-chaining), and added an application-supplied actor_id as the forensic anchor since session_user/current_user are useless under pooling/SECURITY DEFINER (§5.10.3).
+- accepted rA-7: Added a confidentiality/leakage model: mandatory per-wait emit token for approvals (so a leaked id alone cannot forge), hashed workflow_id at rest in audit/DLQ, and a no-raw-logging requirement (§5.11).
+- accepted rA-8: Scoped the flat-dead-tuple headline to await-light loops, conceded coordination-point-bounded dead-tuple rate for await/join-heavy workloads, and added an await/join-heavy A/B to the benchmark (§5.6, §6.5).
+- accepted rA-9: Added an explicit minimum PgQ engine floor (send_at + durable retry counter + tick-visibility) gated and failing loudly at install, alongside the PG 14–18 matrix (§5.9, §5.13, §10).
+- accepted rB-1: Introduced a mandatory minimal wf_registry as the authoritative emit-liveness source (concurrency-bounded, one insert+delete per workflow lifetime), so unknown-id rejection no longer depends on the optional wf_live projection (§5.5, §5.10.2, §5.12).
+- accepted rB-2: Pinned retry continuations to a fresh step_seq with retry_attempt/origin_step in the payload, so the dedup model re-executes the retry instead of treating it as a committed no-op (§5.1, §5.2, §5.4).
+- accepted rB-3: Pinned the load-bearing definition: the age clock is the per-event delivery_anchor (deliverable time), not workflow origin, explicitly reset across sleeps — resolved jointly with rA-1 (§5.4.1).
+- accepted rB-4: Separated cache_retention_horizon (emit→registration gap) from the user-facing await_timeout, so a long await is no longer capped by cache retention and is not rejected at registration (§5.7.2).
+- accepted rB-5: Added the mandatory symmetric positive test asserting a sleep longer than dedup_horizon resumes normally and is NOT DLQ'd (§6.2 item 2).
+- accepted rB-6: Specified the isolation mechanism (dispatcher fault-isolation re-dispatch over the same snapshot range) and pinned the durable per-event retry counter as an engine contract — resolved jointly with rA-2 (§5.2, §5.9).
+- accepted rB-7: Restated timeout liveness as conditional on a continuously-running dispatcher, with pg_cron required for scale-to-zero — resolved jointly with rA-3 (§5.7.1).
+- accepted rB-8: Reframed the CSPRNG check as a decidable static assertion: id column defaulted by gen_random_uuid()/pgcrypto and CI rejects any sequence/serial-derived id path (§5.11, §6.2 item 6).
+- accepted rB-9: Corrected the cross-reference: the no-subtransaction constraint is cited to §5.1/§5.13, not §5.10 (§5.2).
+- accepted rB-10: Populated the canonical architecture:begin/end block with the layered diagram, removing the stale '(architecture not yet specified)' placeholder (§4).
+- accepted rB-11: Added an assertion that a transient-failure step re-executes its body once per retry attempt up to max_retries then lands in the DLQ, guarding the dedup-vs-retry path (§6.2 item 3).
+
+## Round 3 — 2026-05-30T11:37:14.368Z
+
+- accepted rB-1: Actually populated the canonical architecture:begin/end block with the layered SDK→durable-layer→sacred-engine diagram, replacing the literal '(architecture not yet specified)' placeholder the v0.3 changelog had falsely claimed filled (§4).
+- accepted rB-2: Removed the 'tens of thousands of transitions/sec' / 'not throughput-timid' framing from §1/§2 and aligned all of §1, §2, and §12 to the idea's honest concession of ~a few thousand transitions/sec per database with hyperscale conceded to Temporal.
+- accepted rB-3: Redesigned poison-pill containment to use only the existing next_batch max_events bound (reduce to size 1), withdrawing the implied sub-range/partial-ack primitive, and pinned that bound as explicit engine contract #4 gated at install (§5.2/§5.9/§5.13).
+- accepted rB-4: Pinned per-join completion serialization (SELECT … FOR UPDATE / advisory lock on the join id) at READ COMMITTED so the final concurrent completers are ordered and the parent resumes exactly once — closing the lost-resume (zero-resume) race (§5.8).
+- accepted rB-5: Added an engine-contract regression test for the next_batch max_events bound (contract #4) plus a multi-tenant batch poison-isolation test asserting innocent co-tenants are not DLQ'd, and an install-floor gate covering all four contracts (§6.2/§6.3).
+- accepted rB-6: Dropped the undefined 'within-horizon pre-registration' clause; live wf_registry membership (held for a workflow's whole lifetime) is the sole emit-liveness source and already covers emit-before-await (§5.10.2/§5.12).
+- accepted rB-7: Reduced the 'all clients get workflows' claim to the single Python reference client actually staffed/scheduled, with Go/TS/WIP clients explicitly deferred, making §1/§2/§9/§11/§12 consistent with §7/§8 (§1/§2).
+
+## Round 4 — 2026-05-30T11:56:01.783Z
+
+- accepted contradiction#1: Pasted a real layered architecture diagram into the §4 architecture:begin/end block and corrected the false v0.4 changelog claim to admit the placeholder had remained, ending the twice-repeated conflict between the changelog and the actual block.
+- accepted ambiguity#1: Moved the poison-pill max_events reduction from process-local dispatcher state into a new consumer-wide wf_dispatch_control row read by every subconsumer before each next_batch, so a redelivered poison event cannot be re-aggregated at K by another subconsumer, and added a multi-subconsumer redelivery test plus a cross-subconsumer clause to engine contract #4.
+- accepted ambiguity#2: Specified the up-ramp: current_max_events is restored to K only after quarantine_cooldown consecutive clean size-1 commits (count-gated, not time-gated) so the poison is DLQ'd before batches re-aggregate, with a regression test for the restoration.
+- accepted contradiction#2: Withdrew the inconsistent 'append-based, rotating, not insert+delete' description and pinned wf_live as a single one-row-per-live-workflow HOT-UPDATEd projection (concurrency-bounded row-count; dead-tuple rate = update rate) so §4.2, §5.5, and §5.6 agree.
+- accepted ambiguity#3: Pinned the §5.4.1 staleness check as a pre-body, route-not-process gate that commits cleanly before any user body runs, scoped the contract-#2 'only durable counter' claim to the aborting-batch channel only, reconciling the two DLQ routes and adding a gate-ordering test.
diff --git a/blueprints/workflows/index.html b/blueprints/workflows/index.html
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+++ b/blueprints/workflows/index.html
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+<!doctype html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
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+<title>Brief — PgQue Durable Workflows — SPEC v0.5 (v0.5)</title>
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+<body>
+<div class="progress" aria-hidden="true"><i id="pb"></i></div>
+<header class="metabar">
+<div class="metabar-row">
+<div class="metabar-left">
+<span class="brand">workflows</span>
+<span class="chip">v<b>v0.5</b></span>
+<span class="chip">2026-05-30</span>
+</div>
+<div class="metabar-right">
+<span class="status">brief</span>
+<span class="theme-sw" role="group" aria-label="Theme">
+<button data-v="light" title="Light">&#9728;</button>
+<button data-v="dark" title="Dark">&#9790;</button>
+<button data-v="auto" title="System" class="active">&#9680;</button>
+</span>
+</div>
+</div>
+</header>
+<main class="brief">
+<header class="brief-hero">
+<p class="brief-kicker">Brief — derivative summary</p>
+<h1 class="brief-title">PgQue Durable Workflows — SPEC v0.5</h1>
+<p class="brief-subtitle">
+<code>workflows</code> ·
+ Version v0.5 ·
+ Published <time>2026-05-30T09:41:56.622Z</time> ·
+ <a href="./SPEC.md">canonical SPEC.md →</a>
+</p>
+<p class="brief-warning">
+Summary, not the spec. Skim this for shape, architecture, scope, risks, decisions, and open questions in 5–10 minutes; consult <a href="./SPEC.md">SPEC.md</a> for the full text.
+</p>
+</header>
+<nav class="brief-toc">
+<div class="brief-toc-title">In this brief</div>
+<ol>
+<li><a href="#s-goal"><span class="num">01</span><span>Goal</span></a></li>
+<li><a href="#s-1-goal-why-it-s-needed"><span class="num">02</span><span>1. Goal &amp; why it&#39;s needed</span></a></li>
+<li><a href="#s-2-scope-resolved-interview-decisions"><span class="num">03</span><span>2. Scope &amp; resolved interview decisions</span></a></li>
+<li><a href="#s-3-user-stories"><span class="num">04</span><span>3. User stories</span></a></li>
+<li><a href="#s-4-architecture"><span class="num">05</span><span>4. Architecture</span></a></li>
+<li><a href="#s-5-implementation-details"><span class="num">06</span><span>5. Implementation details</span></a></li>
+<li><a href="#s-6-tests-plan"><span class="num">07</span><span>6. Tests plan</span></a></li>
+<li><a href="#s-7-team-veteran-experts-to-hire"><span class="num">08</span><span>7. Team (veteran experts to hire)</span></a></li>
+<li><a href="#s-8-implementation-plan-sprints-parallelization-ordering"><span class="num">09</span><span>8. Implementation plan (sprints, parallelization, ordering)</span></a></li>
+<li><a href="#s-9-topic-specific-api-surface-reference-sdk-python-v0-1"><span class="num">10</span><span>9. Topic-specific: API surface (reference SDK, Python v0.1)</span></a></li>
+<li><a href="#s-10-operability-notes-managed-pg"><span class="num">11</span><span>10. Operability notes (managed-PG)</span></a></li>
+<li><a href="#s-11-open-items-carried-to-v0-6"><span class="num">12</span><span>11. Open items carried to v0.6</span></a></li>
+<li><a href="#s-12-non-goals-disclaimers-honored-strictly-not-reintroduced-anywhere-above"><span class="num">13</span><span>12. Non-goals / disclaimers (honored strictly — not reintroduced anywhere above)</span></a></li>
+<li><a href="#s-13-embedded-changelog"><span class="num">14</span><span>13. Embedded Changelog</span></a></li>
+</ol>
+</nav>
+<section class="brief-goal" id="s-goal">
+<h2><span class="n">01</span><span>Goal</span></h2>
+<p>&gt; Status: <strong>experimental</strong>, ships as optional <code>sql/experimental/durable.sql</code> gated by the project promotion rule. Workflow support ships first as <strong>one thin-SQL-wrapper reference client (Python)</strong>; the other PgQue clients (Go, TypeScript, + WIP) are a planned follow-up, not v0.1 (§7–§9, §12). Engine layer is sacred and untouched.</p>
+</section>
+<section class="brief-section brief-section-generic" id="s-1-goal-why-it-s-needed">
+<h2><span class="n">02</span><span>1. Goal &amp; why it&#39;s needed</span></h2>
+<p><strong>Goal (user-outcome language).</strong> Give developers durable, crash-proof workflows — multi-step processes and AI-agent loops that never lose progress and run exactly-once — using only the Postgres they already operate, with no separate system to run, and that <strong>keep running fast under sustained high volume instead of degrading over time</strong> (no gradual slowdown, no VACUUM wall, no throughput cliff, no tuning, no 3am pager).</p>
+<p><strong>Positioning.</strong> This is a <strong>lighter, no-new-infra, stays-fast alternative to Temporal and DBOS</strong> — it competes with them head-on on durable execution and delivers the same core guarantees teams adopt those systems for (durable multi-step execution, exactly-once handoff, at-least-once steps, durable timers, fan-out/join), running entirely inside your existing managed Postgres and <strong>not slowing down under load</strong>. Eliminating per-step <code>workflow_status</code> <code>UPDATE</code> churn is the <strong>headline benefit</strong>, not a limitation. We compete on durability; we differ only in <em>mechanism</em> (explained as the <em>how</em> below, never sold as the <em>what</em>). Throughput target: <strong>tens of thousands of simple (await-light) transitions/sec per database, flat under sustained load</strong> (higher with batching), with the headline being that it <strong>does not degrade</strong> where status-row systems hit the VACUUM wall; coordination-heavy (await/join) transitions cost more and are characterized honestly (§5.6). Beyond a single node, scale out by <strong>sharding workflows across databases</strong>.</p>
+<p><strong>Why this exists.</strong> Every Postgres-native durable-execution engine in the category (DBOS, absurd, and the long tail of <code>SELECT … FOR UPDATE SKIP LOCKED</code> + <code>DELETE</code> queues) shares one structural liability: they model a workflow as a <strong>mutable <code>workflow_status</code> row that is <code>UPDATE</code>d on every step</strong>. At the throughput the category is actually chasing — AI agent loops doing millions of cheap iterations — that per-step <code>UPDATE</code> churns dead tuples until the workload hits a VACUUM wall, and throughput degrades. The result users feel is a system that is fast in the demo and slow in month three. PgQ already solved exactly this for <em>queues</em> with snapshot-batch isolation + wholesale <code>TRUNCATE</code> rotation: zero dead-tuple bloat under sustained load. This product carries that property up to the workflow layer.</p>
+</section>
+<section class="brief-section brief-section-decisions" id="s-2-scope-resolved-interview-decisions">
+<h2><span class="n">03</span><span>2. Scope &amp; resolved interview decisions</span></h2>
+<p>The interview answers were all delegated to the lead (&quot;decide for me&quot;). Resolved:</p>
+<table class="md-table"><thead><tr><th>Question</th><th>Decision (v0.1, carried through)</th></tr></thead><tbody><tr><td><strong>Primary users</strong></td><td>Backend engineers running long-lived or high-iteration orchestration (AI agent loops, multi-step business processes, fan-out jobs) <strong>on managed Postgres</strong> who refuse a second datastore and refuse a VACUUM wall.</td></tr><tr><td><strong>Core job</strong></td><td>Advance a workflow from one step to the next with <strong>exactly-once handoff</strong> and <strong>at-least-once step execution</strong>, never losing or silently duplicating a workflow&#39;s progress — on a hot path that appends and rotates rather than updates.</td></tr><tr><td><strong>Durability / recovery guarantee</strong></td><td>At-least-once step execution + exactly-once handoff between steps; per-step idempotency keyed on <code>(workflow_id, step_seq)</code>. On crash, exactly the single in-flight step redelivers (PgQ&#39;s existing redelivery); there is no long function to replay.</td></tr><tr><td><strong>Success metric</strong></td><td>A throughput-and-bloat benchmark vs a mutable-status-row baseline (DBOS/absurd shape) on server hardware: <strong>flat dead-tuple count + sustained throughput</strong> on the append+rotate hot path where the baseline degrades.</td></tr><tr><td><strong>Out of scope for v0.1</strong></td><td>Cancellation / orphan-join propagation; linear-code (<code>async/await</code>-compiled) DX sugar; the per-language deterministic-replay <em>runtime</em> (we ship one thin SQL-wrapper reference client — Python — instead, §9); additional-language clients (Go/TS/WIP — a deferred follow-up, §11); imposing a determinism requirement on user code. <strong>In scope:</strong> the one Python reference client, the full durability/coordination engine, and the observability surface of §5.14.</td></tr></tbody></table>
+<p>---</p>
+</section>
+<section class="brief-section brief-section-generic" id="s-3-user-stories">
+<h2><span class="n">04</span><span>3. User stories</span></h2>
+<p>Each story is persona + action + outcome and is directly exercised as a manual acceptance test (§6.4).</p>
+<p>---</p>
+<ul>
+<li><strong>Agent-loop builder (stays fast at iteration scale).</strong> <em>As</em> a backend engineer running an AI agent that loops thousands of times per run, <em>I</em> define each iteration as a step that processes and enqueues its successor, <em>so that</em> a million iterations complete with <strong>no gradual slowdown and a flat dead-tuple count</strong> on the hot tables — verifiable with <code>pg_stat_user_tables.n_dead_tup</code> staying flat through the run. (The flat-curve claim is scoped to await-light loops; await/join-heavy shapes are characterized honestly in §5.6.)</li>
+</ul>
+</section>
+<section class="brief-section brief-section-architecture" id="s-4-architecture">
+<h2><span class="n">05</span><span>4. Architecture</span></h2>
+<p>&lt;!-- architecture:begin --&gt;</p>
+<p>&lt;!-- architecture:end --&gt;</p>
+<p>The durable layer <strong>only calls</strong> the PgQ primitives + <code>send_at</code>. It adds <strong>no</strong> modification to rotation/tick/batch logic and introduces <strong>no</strong> second concurrency model. Its dependencies on engine semantics (tick-visibility, durable per-event retry count, <code>send_at</code>, the <code>next_batch</code> max-events bound) are made explicit and pinned by engine-contract tests (§5.9).</p>
+<ul>
+<li><strong>Workflow</strong> — a logical state machine identified by <code>workflow_id</code>, which is a <strong>128-bit unguessable capability</strong> (§5.11), not a sequential id. At any instant it is in exactly one of three conditions: <strong>(a)</strong> one <em>in-flight</em> message (a step-event sitting in a PgQ batch being processed), <strong>(b)</strong> <em>scheduled</em> (a <code>send_at</code> continuation awaiting a wake time, or a registered wait awaiting an event), or <strong>(c)</strong> <em>terminal</em>. The <strong>single-live-continuation invariant</strong> — each processed step enqueues <em>exactly one</em> successor — is what makes exclusivity structural rather than lease-based.</li>
+<li><strong><code>workflow_id</code> — addressing handle AND bearer capability.</strong> It is used both to <em>address</em> a workflow (in payloads, user tables) and, combined with the role grants and per-wait tokens of §5.10, to <em>authorize</em> operations against it. Because it does double duty it must be treated as a secret; §5.11 specifies its confidentiality/leakage model (hashed at rest in audit/DLQ, never logged raw, mandatory token for approval waits).</li>
+<li><strong>Step-event</strong> — the message on the PgQ queue. Payload carries: <code>workflow_id</code>, <code>step_seq</code> (monotonic progress anchor), <code>step_name</code>/state tag, <code>delivery_anchor</code> (the event&#39;s deliverable time, §5.4.1), small continuation state (continuation-passing), and — for retries — <code>retry_attempt</code>/<code>origin_step</code> (§5.2), subject to a <strong>hard payload size cap</strong> (§5.12). <code>workflow_id</code>/<code>step_seq</code>/<code>step_name</code> are also placed in <code>ev_extra1/2/3</code> for indexed observability (§5.14.2). Large state is the user&#39;s responsibility to hold in their own tables, addressed by <code>workflow_id</code>.</li>
+<li><strong>Transition</strong> — process a step → emit successor as a <em>new append</em>. Never an <code>UPDATE</code> of a status row.</li>
+<li><strong>Coordination side tables</strong> (the only mutable state; see §5.5) — <code>wf_registry</code>, <code>wf_wait</code>, <code>wf_event_cache</code>, <code>wf_join</code>, <code>wf_join_done</code>, <code>wf_dedup</code>, <code>wf_audit</code>, the consumer-wide <code>wf_dispatch_control</code> (one row per logical consumer, §5.2), and the <strong>optional, opt-in</strong> <code>wf_live</code> projection. Their churn is bounded by <strong>concurrency and coordination-point count, not total step volume</strong> — stated precisely (distinguishing live row-count from dead-tuple rate, and conceding the await/join-heavy case) in §5.6.</li>
+</ul>
+<pre data-lang="text"><code class="language-text">(architecture not yet specified)</code></pre>
+<details class="brief-subsections">
+<summary>Subsections (3)</summary>
+<ol><li>4.1 Layering (the sacred boundary)</li>
+<li>4.2 Key abstractions</li>
+<li>4.3 Concurrency / ownership model</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-5-implementation-details">
+<h2><span class="n">06</span><span>5. Implementation details</span></h2>
+<p>The foundational guarantee. <code>insert_event()</code> (enqueue successor) and <code>finish_batch()</code> (ack) run in the <strong>consumer&#39;s own transaction</strong>. <strong>The atomic commit unit is the batch transaction</strong> (§5.2); for the common case of a single-event batch it reduces exactly to one step&#39;s side effects + its successor enqueue + its ack committing together:</p>
+<p>The dedup marker is keyed on <em>this attempt&#39;s</em> <code>(workflow_id, step_seq)</code>. A retry continuation is a <strong>new transition with a fresh <code>step_seq</code></strong> (§5.2), so it carries its own marker and is therefore <strong>not</strong> absorbed as a dedup no-op — it re-executes. <strong>No subtransactions are used on this path</strong> (hard constraint; also §5.13).</p>
+<p>The single most important objection, answered head-on. <strong>No</strong> — and the reason is the same batching amortization that makes PgQ itself cheap:</p>
+<ul>
+<li><strong>Commit</strong> ⇒ successor durably enqueued <strong>AND</strong> batch finished, atomically ⇒ exactly-once handoff.</li>
+<li><strong>Crash before commit</strong> ⇒ txn aborts ⇒ no successor, no dedup marker, batch not finished ⇒ the step redelivers cleanly.</li>
+</ul>
+<pre><code>begin;
+  -- 1. step&#39;s own DB side effects (idempotent or naturally in-txn)
+  -- 2. record per-step dedup marker (workflow_id, step_seq)   [if first delivery]
+  perform pgque.insert_event(queue, next_state);   -- enqueue exactly one successor
+  perform pgque.finish_batch(batch_id);            -- ack this batch
+commit;</code></pre>
+<pre><code>loop:
+  K        := dispatch_control.current_max_events           -- shared, consumer-wide (§5.5)
+  batch_id := pgque.next_batch(queue, consumer, max_events := K)   -- snapshot-bounded, ≤ K events
+  if batch_id is null:
+      run_timeout_sweep()                              -- §5.7.1 in-loop liveness
+      sleep to next tick; continue
+  events  := pgque.get_batch_events(batch_id)
+  begin
+    for each event in events:                          -- batch step execution
+        if redelivery_age(event) &gt; dedup_horizon:      -- §5.4.1 staleness GATE, BEFORE body
+            route_to_dlq(event); continue              --   route-not-process: no user body runs
+        advance_one(event)                             -- §5.3, appends successor(s)
+    pgque.finish_batch(batch_id)
+    run_timeout_sweep()                                -- opportunistic
+  commit
+  on abort:  note_batch_abort()                        -- ramps dispatch_control down (below)
+  on clean commit at K=1:  note_clean_isolated_commit() -- ramps dispatch_control back up</code></pre>
+<pre><code>dedup_horizon  ≥  max_retry_backoff        (one attempt&#39;s backoff)
+               +  dead_interval             (worst-case takeover delay)
+               +  max_batch_duration
+               +  safety_margin</code></pre>
+<details class="brief-subsections">
+<summary>Subsections (8)</summary>
+<ol><li>5.1 The hot path: one transition = append + ack, atomically</li>
+<li>5.1.1 The make-or-break rebuttal: &quot;isn&#39;t per-workflow state a per-transition UPDATE, 1:1 with messages → same bloat?&quot;</li>
+<li>5.2 Dispatch loop, transaction boundary, and retry</li>
+<li>5.3 The five durable-execution requirements, mapped</li>
+<li>5.4 Per-step idempotency</li>
+<li>5.5 Coordination side tables</li>
+<li>5.6 The honest zero-bloat / stays-fast claim (row-count vs dead-tuple rate, incl. the await/join-heavy case)</li>
+<li>5.6.1 Honest latency characterization (separate from bloat)</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-6-tests-plan">
+<h2><span class="n">07</span><span>6. Tests plan</span></h2>
+<p><strong>Red/green TDD for ALL new code.</strong> Every function below is written test-first: a failing test asserting the behavior, then the implementation that makes it pass. CI rejects any new SQL function or SDK method without a preceding failing-then-passing test in the same change.</p>
+<p>Each of the six user stories has a runnable scenario script the reviewer executes by hand against a managed-PG-like instance, including the §3.3 forged-approval negative check (with and without the per-wait token), the §3.2 long-sleep-resumes-not-DLQ&#39;d check, the §3.4 concurrent-completer exactly-once-resume check, and the §3.6 observability walkthrough.</p>
+<p>Throughput-and-bloat benchmark vs a mutable-status-row baseline (DBOS/absurd shape) on server hardware. Publishes, over a long sustained run: <strong><code>n_dead_tup</code></strong> (flat for the PgQue await-light hot path; rising for baseline), <strong>sustained transitions/sec</strong> (targeting tens of thousands per database for await-light, flat under sustained load, §1/§5.6.1), the <strong>coordination-table dead-tuple curve</strong>, and an explicit <strong>await/join-heavy A/B workload</strong> that coordinates on (nearly) every step, so the §5.6 scoped headline is substantiated rather than asserted. Because long VACUUM-wall runs are slow and noisy, this is a <strong>nightly / on-demand gated harness</strong>, explicitly out of the per-change CI gate (which runs only a short smoke version). The full harness is reproducible and versioned.</p>
+<ul>
+<li><strong>Exactly-once handoff</strong> (§5.1) — kill the txn between <code>insert_event</code> and <code>commit</code>, assert no successor + clean redelivery; assert no double-handoff on commit.</li>
+<li><strong>Per-step idempotency + dedup-horizon + delivery-anchor clock</strong> (§5.4/§5.4.1) — deliver the same <code>(workflow_id, step_seq)</code> twice → exactly one successor + one side effect; redeliver at horizon-boundary age → routed to DLQ, no double-handoff; <strong>the mandatory positive test: a <code>sleep</code> longer than <code>dedup_horizon</code> resumes normally and is NOT DLQ&#39;d</strong>; <strong>AND the staleness-gate ordering test: the §5.4.1 staleness check runs and commits its DLQ route BEFORE any user body executes, and a stale event is never handed to a body that aborts</strong> (guards the §5.4.1↔§5.2 reconciliation).</li>
+<li><strong>Transaction-boundary / retry resolution</strong> (§5.2) — a retry continuation re-enqueues via <code>send_at</code> with a <strong>fresh <code>step_seq</code></strong> and, on delivery, <strong>re-executes its body</strong> (assert the step logic runs once per retry attempt up to <code>max_retries</code>, then lands in DLQ); an unexpected exception aborts only a bounded batch; <strong>single-dispatcher poison-pill isolation: a poison event sharing a starting batch of size K with several innocent co-tenant workflows is quarantined to the DLQ via consumer-wide <code>max_events</code>-reduction-to-1, and every innocent co-tenant ultimately commits and is NOT DLQ&#39;d</strong>; <strong>AND the multi-subconsumer redelivery test: with ≥2 cooperative subconsumers running, an aborting poison event is redelivered to a DIFFERENT subconsumer than the one that aborted, and the consumer-wide <code>wf_dispatch_control</code> reduction ensures that other subconsumer also requests size-1 batches — assert the poison is NOT re-aggregated with innocents at <code>max_events=K</code> and no innocent co-tenant is forced to the DLQ</strong> (guards the subconsumer-safety fix; exercises engine contract #4 across subconsumers); <strong>AND the quarantine up-ramp test: after <code>quarantine_cooldown</code> clean size-1 commits, <code>current_max_events</code> is restored to K</strong>.</li>
+<li><strong><code>awaitEvent</code> / <code>emit</code> race matrix</strong> (§5.7) — one test per row; <code>cache_retention_horizon</code> never drops a within-horizon entry and is <strong>independent of <code>await_timeout</code></strong> (a long await behind a fast emit is not rejected, §5.7.2); advisory-lock serialization correct under simulated transaction-pooling, including a <strong>hash-collision correctness-safety</strong> test (§5.7.3); single-resume token proven by concurrent emit+sweep.</li>
+<li><strong>fan-out / join</strong> (§5.8) — race-free join-total recording; idempotent completed-set under duplicated completion; <strong>exactly-once parent resume proven with CONCURRENT FINAL COMPLETERS — assert the parent IS resumed exactly once (not zero, not twice), exercising the per-join completion lock at READ COMMITTED</strong>; <strong>per-child result array assembled from <code>wf_join_done</code> (spill) with a resume payload under <code>max_payload_bytes</code> at full <code>max_spawn_fanout</code></strong>; spawn-fanout cap enforced.</li>
+<li><strong>Authorization &amp; capability</strong> (§5.10/§5.11) — PUBLIC cannot execute any durable function; <code>emit</code> without the <code>workflow_id</code> capability fails; <code>emit</code> for an id absent from <code>wf_registry</code> is rejected with no cache row; an approval-class <code>emit</code> without the mandatory per-wait token fails even with a valid id; forged-approval with a guessed sequential id fails; <strong><code>workflow_id</code> column is defaulted by <code>gen_random_uuid()</code>/<code>pgcrypto</code> and CI statically rejects any sequence/serial-derived id path</strong>; <code>wf_audit</code>/DLQ store hashed ids; audit row with <code>actor_id</code> written for every emit/resume/spawn.</li>
+<li><strong>Observability surface</strong> (§5.14) — parked-workflow view returns correct waiting/sleeping/overdue sets; <code>ev_extra1</code>-indexed running-set query returns the in-flight window; <code>wf_audit</code>-derived metrics view returns correct counts; <code>wf_live</code> boundary-granularity reflects start/park/terminal with no per-step write, and high-resolution opt-in reflects exact current step (asserting the per-step <code>UPDATE</code> happens only in high-res mode).</li>
+</ul>
+<details class="brief-subsections">
+<summary>Subsections (5)</summary>
+<ol><li>6.1 Hard repo rule</li>
+<li>6.2 Built test-first, in this order (highest risk first)</li>
+<li>6.3 CI test suites</li>
+<li>6.4 Manual acceptance (maps 1:1 to §3 user stories)</li>
+<li>6.5 Success-criterion benchmark (the entire pitch) — gated, NOT a per-change CI suite</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-7-team-veteran-experts-to-hire">
+<h2><span class="n">08</span><span>7. Team (veteran experts to hire)</span></h2>
+<p>Veteran <strong>&quot;Durable Workflow Engineer&quot;</strong> (accepted).</p>
+<p>---</p>
+<ul>
+<li><strong>Veteran PostgreSQL internals / MVCC engineer (1)</strong> — snapshot/visibility reasoning, <code>xid8</code>/<code>pg_snapshot</code>, rotation interaction, no-subtransaction guarantee, engine-contract tests (§5.9 incl. the <code>next_batch</code> max-events bound and its cross-subconsumer redelivery semantics), engine-floor install gate.</li>
+<li><strong>Veteran durable-execution / distributed-systems engineer (1)</strong> — await/emit and fan-out/join race designs, single-resume-token proofs, the join-completion serialization + lost-resume closure (§5.8), the dedup-horizon + delivery-anchor bound (§5.4.1), the transaction-boundary/retry resolution incl. retry-<code>step_seq</code> semantics and the consumer-wide <code>wf_dispatch_control</code> poison-pill <code>max_events</code> size-1 isolation + up-ramp recovery (§5.2).</li>
+<li><strong>Veteran PostgreSQL security engineer (0.5, shared)</strong> — authorization model (§5.10), capability generation + confidentiality/leakage model (§5.11), mandatory per-wait token, audit attribution under pooling, grant-audit tests, resource caps (§5.12).</li>
+<li><strong>Veteran PL/pgSQL + SQL test engineer (pgTAP) (1)</strong> — red/green TDD harness, concurrency/property tests (incl. concurrent-completer join liveness AND multi-subconsumer poison-isolation), crash-recovery + pg_cron-disabled and scale-to-zero liveness injection, the positive long-sleep-not-DLQ&#39;d, staleness-gate-ordering, retry-re-execution, and quarantine up-ramp tests.</li>
+<li><strong>Veteran SDK / developer-experience engineer (Python) (1)</strong> — the one reference SDK and the thin-client surface, incl. <code>awaitAll</code> result-array assembly from the spill table; the SDK side of the observability surface.</li>
+<li><strong>Veteran observability / SRE engineer (0.5, shared)</strong> — the §5.14 views, <code>ev_extra1</code> index, <code>wf_audit</code>→OTel/Prometheus/ClickHouse export pipeline, workflows-overview + DLQ inspection.</li>
+<li><strong>Veteran performance / benchmarking engineer (1)</strong> — the gated throughput-and-bloat benchmark incl. the await/join-heavy A/B and the published curves.</li>
+<li class="brief-more">…1 more in SPEC.md</li>
+</ul>
+<details class="brief-subsections">
+<summary>Subsections (1)</summary>
+<ol><li>7.1 Persona for this spec round</li></ol>
+</details>
+</section>
+<section class="brief-section brief-section-generic" id="s-8-implementation-plan-sprints-parallelization-ordering">
+<h2><span class="n">09</span><span>8. Implementation plan (sprints, parallelization, ordering)</span></h2>
+<p><strong>Sprint 0 — Foundations &amp; harness (1 wk).</strong></p>
+<p><strong>Sprint 1 — Exactly-once core (1.5 wk).</strong> <em>(highest risk first)</em></p>
+<p><strong>Sprint 2 — Coordination primitives (2 wk).</strong> <em>Two parallel tracks:</em></p>
+<ul>
+<li>Test engineer: pgTAP red/green harness, CI matrix (PG 14–18), engine-sacredness diff-guard, grant-audit scaffold. <em>(blocks everyone.)</em></li>
+<li>PG-internals engineer: spike the primitive reduction; confirm <code>send_at</code> (PR #237), the durable per-event retry counter, <strong>and the <code>next_batch</code> max-events bound incl. cross-subconsumer redelivery (contract #4)</strong>; draft the engine-contract tests + install-time engine-floor gate (§5.9).</li>
+<li>Security engineer: role model + <code>REVOKE</code>-from-PUBLIC install template + capability generation and leakage-hygiene defaults (§5.11).</li>
+<li><em>Parallel:</em> SDK engineer scaffolds the thin Python client against stub SQL signatures.</li>
+</ul>
+</section>
+<section class="brief-section brief-section-generic" id="s-9-topic-specific-api-surface-reference-sdk-python-v0-1">
+<h2><span class="n">10</span><span>9. Topic-specific: API surface (reference SDK, Python v0.1)</span></h2>
+<p>Every SDK call compiles to one of the PgQ primitives + a coordination-table touch, subject to the authorization (§5.10) and resource (§5.12) checks. The programming model is a message-driven <strong>state machine</strong> (think AWS Step Functions / actors). <strong>One reference client (Python) in v0.1; other-language clients (Go/TS/WIP) are a deferred follow-up</strong> (§11/§12) — cheap to add later precisely because durability lives in SQL and each client is a thin wrapper, kept aligned by a shared cross-client conformance suite. <strong>No</strong> <code>async/await</code>-compiled linear-code DX in v0.1 (deferred, §12).</p>
+<p>---</p>
+<pre data-lang="python"><code class="language-python">wf = defineWorkflow(&quot;order_fulfillment&quot;)
+
+@wf.step(&quot;charge&quot;)
+def charge(ctx, state):
+    ctx.side_effect(...)              # user&#39;s own idempotent/in-txn write
+    return ctx.goto(&quot;await_ship&quot;, state)        # append successor
+
+@wf.step(&quot;await_ship&quot;)
+def await_ship(ctx, state):
+    return ctx.await_event(&quot;shipped&quot;, timeout=&quot;24h&quot;,
+                           on_event=&quot;notify&quot;, on_timeout=&quot;escalate&quot;,
+                           require_token=True)   # mandatory token for approval-class
+
+@wf.step(&quot;fan&quot;)
+def fan(ctx, state):
+    return ctx.spawn([...N children...], join=&quot;collect&quot;)   # N ≤ max_spawn_fanout
+
+@wf.step(&quot;collect&quot;)
+def collect(ctx, state):
+    results = ctx.join_results()      # assembled from wf_join_done spill (§5.8)
+    ...
+
+# authorized external producer (role: pgque_durable_client), holding the capability + wait token:
+emit(workflow_id, &quot;shipped&quot;, payload, token=wait_token, actor_id=&quot;svc:shipping&quot;)</code></pre>
+</section>
+<section class="brief-section brief-section-generic" id="s-10-operability-notes-managed-pg">
+<h2><span class="n">11</span><span>10. Operability notes (managed-PG)</span></h2>
+<p>---</p>
+<ul>
+<li><strong>pg_cron — required for scale-to-zero (§5.7.1).</strong> For always-on-dispatcher topologies it is an optimization; for serverless / scale-to-zero, pg_cron driving <code>run_timeout_sweep()</code> is a <strong>correctness requirement</strong> for timeout liveness. The install script warns if neither a long-running dispatcher nor pg_cron is configured.</li>
+<li><strong>Engine floor (§5.9/§5.13):</strong> install gates on the minimum PgQ engine version — <code>send_at</code> present, durable per-event retry counter exposed, tick-visibility per contract, <code>next_batch</code> honoring the <code>max_events</code> bound (incl. cross-subconsumer redelivery) — and fails loudly otherwise.</li>
+<li><strong>Poison-pill quarantine is consumer-wide (§5.2).</strong> Operators should know that a persistently-aborting (poison) event transiently collapses the <em>entire logical consumer</em> to size-1 batches until the event is DLQ&#39;d and <code>quarantine_cooldown</code> clean commits restore throughput — a brief, self-healing throughput dip, not a per-process anomaly. <code>quarantine_cooldown</code> and starting <code>K</code> are documented tunables.</li>
+<li><strong>Required operator settings:</strong> documented autovacuum tuning for the <code>DELETE</code>-driven coordination tables (<code>wf_registry</code>, <code>wf_wait</code>, <code>wf_join</code>) and for <code>wf_live</code> if enabled (HOT-update churn at its configured granularity, §5.5) so their dead-tuple rate (§5.6) stays bounded; rotation cadence for <code>wf_dedup</code>/<code>wf_event_cache</code>/<code>wf_audit</code>. The await/join-heavy dead-tuple characterization (§5.6) is documented so operators size autovacuum for their workload shape.</li>
+<li><strong>Observability (§5.14):</strong> enable the optional <code>ev_extra1</code> index for the running-set view; wire the <code>wf_audit</code> export to OTel/Prometheus/ClickHouse; choose <code>wf_live</code> granularity (boundary default vs per-step opt-in) per the bloat/visibility trade.</li>
+<li><strong>Capability-leakage hygiene (§5.11):</strong> disable statement-parameter logging for the durable schema; <code>workflow_id</code> is stored hashed in <code>wf_audit</code> and DLQ; treat the id as a secret and prefer the mandatory per-wait token for approvals.</li>
+<li><strong>Audit export (§5.10.3):</strong> the <code>wf_audit</code> rotating table must be exported to durable storage before rotation; export hook + retention policy are part of the docs. Honest limitation: the log is append-only-by-convention, not cryptographically tamper-evident (hash-chaining deferred, §11).</li>
+<li class="brief-more">…1 more in SPEC.md</li>
+</ul>
+</section>
+<section class="brief-section brief-section-generic" id="s-11-open-items-carried-to-v0-6">
+<h2><span class="n">12</span><span>11. Open items carried to v0.6</span></h2>
+<p>---</p>
+<ul>
+<li>Quantitative defaults for every configured bound (<code>dedup_horizon</code>, <code>cache_retention_horizon</code>, <code>max_spawn_fanout</code>, <code>max_payload_bytes</code>, emit rate, starting batch <code>K</code>, <code>quarantine_cooldown</code>) validated against the benchmark.</li>
+<li>Per-wait emit-token issuance/rotation/revocation detail (§5.10.2) — now mandatory for approval-class, but the token lifecycle is still to be fully specified.</li>
+<li><strong>Audit hash-chaining / signing</strong> for genuine tamper-evidence (§5.10.3) — deferred enhancement beyond append-only-by-convention.</li>
+<li><strong>A verification pass on the v0.5 fix-induced redesigns before promotion</strong> — specifically: the consumer-wide <code>wf_dispatch_control</code> poison-pill isolation + up-ramp recovery across subconsumers (§5.2, new table, new multi-subconsumer test) and its interaction with engine contract #4&#39;s cross-subconsumer redelivery (§5.9); the unified <code>wf_live</code> one-row-per-live-workflow HOT-update model (§5.5); and the §5.4.1↔§5.2 staleness-gate-ordering / dual-DLQ-route reconciliation. These want independent confirmation — including whether a single shared <code>wf_dispatch_control</code> row becomes a write-contention point under many subconsumers + frequent aborts (expected rare, but unmeasured).</li>
+<li>Other-language clients (Go, TypeScript, + WIP) as thin SQL wrappers + the shared cross-client conformance suite — deferred follow-up after the Python reference client (§9/§12).</li>
+<li>Cancellation / orphan-join propagation remains deferred (§12).</li>
+</ul>
+</section>
+<section class="brief-section brief-section-scope-out" id="s-12-non-goals-disclaimers-honored-strictly-not-reintroduced-anywhere-above">
+<h2><span class="n">13</span><span>12. Non-goals / disclaimers (honored strictly — not reintroduced anywhere above)</span></h2>
+<p>---</p>
+<ul>
+<li><strong>Mechanism distinction (NOT a competitive disclaimer).</strong> PgQue Durable Workflows is a direct, better, no-new-infra, stays-fast <strong>alternative to Temporal and DBOS</strong> — it competes with them and delivers the same core durable-execution guarantees (§1). It deliberately does <strong>not</strong> reproduce their <em>durability mechanism</em>: deterministic replay of a long-lived linear function backed by a <code>workflow_status</code> row mutated on every step. That mechanism is precisely the source of the per-step <code>UPDATE</code> bloat we exist to eliminate. <strong>Eliminating per-step <code>UPDATE</code> churn is a goal/benefit (§1), never a non-goal.</strong> What we disclaim is only the <em>technique</em>: no determinism requirement imposed on user code, and no replay-of-a-linear-function programming model in v0.1 (a continuation-compiling SDK is deferred).</li>
+<li><strong>NOT</strong> a per-language deterministic-replay <em>runtime</em> like Temporal&#39;s heavy per-language engines. Workflow support is intended to ship across all PgQue clients eventually as <strong>thin SQL wrappers</strong> (the architecture makes that cheap), but <strong>v0.1 ships one reference client — Python</strong>; Go/TypeScript/WIP are a deferred follow-up (§9/§11), not part of the v0.1 scope or team.</li>
+<li><strong>NOT</strong> a separate server, daemon, or external datastore. No Cassandra, RocksDB, FoundationDB, or Redis.</li>
+<li><strong>Throughput is NOT conceded to a low ceiling.</strong> Target: <strong>tens of thousands of simple (await-light) transitions/sec per database, flat under sustained load</strong> (higher with batching); coordination-heavy transitions cost more and are characterized honestly (§5.6); scale beyond a single node by sharding workflows across databases — that is scale-out, not an apology. The single-workflow sequential rate is ~tick-rate and is stated plainly (§5.6.1) so the aggregate claim is not misread.</li>
+<li><strong>NOT</strong> changing the sacred PgQ engine, and <strong>NOT</strong> introducing a second <code>SELECT … FOR UPDATE SKIP LOCKED</code> claim/lease concurrency model as the primary mechanism — exclusivity comes from the single-live-continuation invariant over the existing rotation engine. (The transaction-scoped advisory lock of §5.7.3, the per-join <code>SELECT … FOR UPDATE</code>/advisory lock of §5.8, and the single per-consumer <code>wf_dispatch_control</code> row of §5.2 are coordination-table serialization/control primitives, <strong>not</strong> a workflow-claim/lease mechanism.)</li>
+<li><strong>Cancellation / orphan-join propagation is deferred</strong> to a follow-up, not in v0.1.</li>
+<li>Linear-code (<code>async/await</code>-compiled) DX is an explicit <strong>later</strong> SDK project, not an engine requirement.</li>
+</ul>
+</section>
+<section class="brief-section brief-section-generic" id="s-13-embedded-changelog">
+<h2><span class="n">14</span><span>13. Embedded Changelog</span></h2>
+<ul>
+<li><strong>v0.5</strong> (2026-05-30) — Closed the two blocking findings + three minors Reviewer B raised against v0.4 (Reviewer A unavailable this round), and re-aligned the user-facing framing to the idea&#39;s hard rules. <strong>GENUINELY populated the §4 canonical architecture block</strong> with the layered SDK→durable-layer→sacred-engine diagram inside the <code>architecture:begin/end</code> markers — correcting a twice-repeated regression where the v0.3 and v0.4 changelogs each falsely claimed the block was filled while the literal &quot;(architecture not yet specified)&quot; placeholder remained; this entry&#39;s claim is verifiable against §4 as written (the prior false v0.4 claim is corrected in the v0.4 entry below). <strong>Made the poison-pill isolation subconsumer-safe</strong>: the v0.4 <code>max_events</code>-reduction-to-1 was process-local dispatcher state, so under the mandated cooperative <em>subconsumers</em> (§4.3) a redelivered poison event could be re-aggregated with innocents by a subconsumer still at <code>max_events=K</code>; v0.5 moves the bound into a new <strong>consumer-wide <code>wf_dispatch_control</code> row</strong> (one row per logical consumer, written in a separate committed txn that survives the abort, read by every subconsumer before each <code>next_batch</code>) so the reduction is uniform across all subconsumers, and added a <strong>multi-subconsumer redelivery test</strong> (§6.2 item 3, §6.3) plus the cross-subconsumer redelivery clause to engine contract #4 (§5.9). <strong>Specified the <code>max_events</code> up-ramp/recovery policy</strong> (§5.2): restore to <code>K</code> after <code>quarantine_cooldown</code> consecutive clean size-1 commits (count-gated, not time-gated). <strong>Unified the <code>wf_live</code> model</strong> (§4.2/§5.5/§5.6): withdrew the inconsistent &quot;append-based, rotating, not insert+delete&quot; description and pinned it as a <strong>one-row-per-live-workflow HOT-<code>UPDATE</code>d projection</strong>. <strong>Reconciled the two DLQ-routing mechanisms and pinned ordering</strong> (§5.4.1/§5.2): the staleness gate is a pre-body, route-not-process check that commits cleanly before any user body runs; the engine retry counter (contract #2) is the abort-channel route after a body has run and aborted. <strong>Re-led with user outcomes</strong> per the idea&#39;s hard framing rule: §1 Goal/positioning rewritten in stays-fast/no-new-infra/crash-proof outcome language with the event-sourcing mechanism demoted to a &quot;How it works&quot; subsection; <strong>restored the idea&#39;s ambitious throughput target</strong> (tens of thousands of await-light transitions/sec per database, scale-out by sharding) and <strong>removed the &quot;a few thousand / conceded to Temporal&quot; framing</strong> the idea explicitly forbids; <strong>added the make-or-break per-transition-UPDATE rebuttal as a dedicated subsection</strong> (§5.1.1); <strong>added the honest single-workflow latency characterization</strong> (§5.6.1); <strong>added the mandated Observability section</strong> (§5.14) with a sixth on-call user story (§3.6), observability tests (§6.2 item 7), and an observability/SRE half-hire (§7). Updated team/plan/tests/open-items/ops accordingly. All five Reviewer B findings accepted.</li>
+<li><strong>v0.4</strong> (2026-05-30) — Closed all seven findings Reviewer B raised against v0.3 (Reviewer A unavailable this round). <strong>NOTE (corrected in v0.5): this entry originally claimed the §4 architecture diagram was &quot;actually populated&quot; — that claim was false; the literal &quot;(architecture not yet specified)&quot; placeholder in fact remained, repeating the identical false claim the v0.3 entry made. The block was genuinely filled only in v0.5.</strong> Corrected throughput positioning to the (later-reverted) &quot;a few thousand transitions/sec&quot; framing; <strong>v0.5 reverts this back to the idea&#39;s ambitious target.</strong> Redesigned poison-pill containment to use <strong>only the existing <code>next_batch</code> <code>max_events</code> bound (reduce to size 1)</strong> for isolation, withdrawing the v0.3 &quot;re-process the same snapshot range with the batch split&quot; framing; added the <code>next_batch</code> max-events bound as <strong>explicit engine contract #4</strong> (§5.9). <strong>(Defect found in v0.5 review: the v0.4 reduction was process-local and not subconsumer-safe — fixed in v0.5 via <code>wf_dispatch_control</code>.)</strong> Closed the fan-out/join <strong>lost-resume race</strong>: completion counting now serializes on the <code>wf_join</code> row (<code>SELECT … FOR UPDATE</code> / per-join advisory lock) at <strong>READ COMMITTED</strong>, and added a concurrent-final-completer liveness test (§5.8/§6.2/§6.3). Removed the undefined &quot;within-horizon pre-registration&quot; emit-authz clause as redundant. Reduced the client-scope claim to the <strong>one Python reference client</strong> actually staffed. Updated team, plan, tests, open items accordingly. All seven Reviewer B findings accepted.</li>
+<li><strong>v0.3</strong> (2026-05-30) — Closed the fix-induced contradictions both reviewers raised against v0.2. Redefined dedup-horizon enforcement around a per-transition <code>delivery_anchor</code> so long <code>send_at</code> sleeps are never misclassified as stale redeliveries and DLQ&#39;d, and recomputed the bound as single-attempt (§5.4.1). Pinned retry continuations to a fresh <code>step_seq</code> so they re-execute instead of being swallowed as a dedup no-op (§5.2/§5.4). Redesigned poison-pill containment onto the engine&#39;s durable per-event retry counter (§5.2), pinned as an explicit engine contract (§5.9). Replaced the unbounded per-key lock row with a transaction-scoped advisory lock (§5.7.3). Separated <code>cache_retention_horizon</code> from <code>await_timeout</code> (§5.7.2). Spilled per-child join results to <code>wf_join_done</code> (§5.8). Made timeout liveness an explicit operator invariant — pg_cron REQUIRED for scale-to-zero (§5.7.1, §10). Introduced a mandatory <code>wf_registry</code> as the authoritative emit-liveness source (§5.5/§5.10.2/§5.12). Added a <code>workflow_id</code> confidentiality/leakage model (§5.11). Corrected the audit overclaim and added <code>actor_id</code> attribution (§5.10.3). Scoped the flat-dead-tuple headline to await-light loops (§5.6/§6.5). Stated a minimum PgQ engine floor (§5.9/§5.13). Attempted to fill the empty §4 architecture block (placeholder in fact remained — corrected in v0.5). All findings from both reviewers accepted.</li>
+<li><strong>v0.2</strong> (2026-05-30) — Hardening round against Reviewer A (security/ops). Added authorization model (§5.10) and <code>workflow_id</code>-as-unforgeable-capability (§5.11). Stated the dedup-horizon bound and its DLQ enforcement (§5.4.1). Resolved the batch-transaction vs per-event-retry contradiction (§5.2). Made timeout liveness a non-optional property of the dispatch loop (§5.7.1). Pinned the await/emit lock to a pooler-safe transaction-scoped lock (§5.7.3). Bounded <code>wf_event_cache</code> retention (§5.7.2). Demoted <code>wf_live</code> to optional/opt-in (§5.5). Refined the zero-bloat claim (§5.6). Added resource caps (§5.12). Stated the engine tick-visibility coupling as a regression-tested contract (§5.9). Scoped the benchmark out of per-change CI (§6.5). Added security engineer, operability section (§10), open-items (§11). Reviewer B unavailable this round.</li>
+<li><strong>v0.1</strong> (2026-05-30) — Initial spec scaffold fleshed into full structure. Resolved all five delegated interview questions. Added Goal-&amp;-why framing, user stories, layered architecture with the sacred-engine boundary, hot-path/coordination detail incl. the honest zero-bloat correction, await/emit + fan-out/join race designs, red/green TDD-first ordering, team roster, 5-sprint plan, SDK surface, and strict non-goals. No reviewer findings yet (first authoring round).</li>
+</ul>
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