diff --git a/canon/principles/async-by-default-for-long-running-tools.md b/canon/principles/async-by-default-for-long-running-tools.md
new file mode 100644
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@@ -0,0 +1,56 @@
+---
+uri: klappy://canon/principles/async-by-default-for-long-running-tools
+title: "Async by Default — Long-Running MCP Tools Return an Identifier, Never Block"
+audience: canon
+exposure: nav
+tier: 2
+voice: neutral
+stability: evolving
+tags: ["canon", "principle", "mcp-server", "async", "long-running", "latency", "vodka-architecture"]
+derives_from:
+  - klappy://canon/principles/partial-data-with-transparency-and-background-warm
+  - klappy://canon/principles/vodka-architecture
+  - klappy://canon/values/axioms
+complements:
+  - klappy://canon/principles/partial-data-with-transparency-and-background-warm
+status: active
+---
+
+# Async by Default — Long-Running MCP Tools Return an Identifier, Never Block
+
+> Any MCP tool whose work could exceed ~5 seconds wall-clock returns an identifier within that budget and places the long-running work behind a separate read tool. No tool blocks for the duration of work.
+
+## The Principle
+
+Three minimum-viable tools result for any long-running action:
+
+1. `<verb>(...)` — submit; returns identifier within ~5 seconds
+2. `get_<verb>_status(id)` — poll; returns current state, progress, and result-when-complete
+3. `cancel_<verb>(id)` — request cancellation; returns ack
+
+Notification-style push (server-pushed events on supported transports) is additive. The polling tool remains the canonical floor so consumers on poll-only transports work too.
+
+## Latency Budget Recommendation
+
+- **Submission tool returns**: ≤ 1s median, ≤ 5s p99
+- **Status read tool returns**: ≤ 1s median (state read, never reaches the worker that does the work)
+- **Notification delivery (when present)**: ≤ 1s median, ≤ 5s p99
+- **Long-poll fallback**: ≤ 5s p99 round-trip
+
+## Failure Mode — Blocking the Consumer
+
+A tool that blocks for 30 minutes ties up the consumer's MCP session, hides progress, breaks cancellation, and forces every consumer host to implement timeout/retry around it. Returning an identifier immediately keeps the wire predictable and the consumer in control of when to ask for results.
+
+The shape also keeps the *server* in control of how long the work continues if the consumer disconnects. With a blocking tool, the work dies on disconnect; with the async shape, the work continues, the cache populates, and the next consumer's request finds the result without re-running the work.
+
+## Relationship to Adjacent Canon
+
+`canon/principles/partial-data-with-transparency-and-background-warm` is the read-side complement: the user-blocking *read* path must not block on a corpus scan; return what's already observed, schedule the rest in the background, disclose what's missing. This principle is the action-side: the user-blocking *action* path must not block for the duration of the work; return an identifier, expose poll+cancel, let the consumer drive their own attention.
+
+Both principles share the underlying axiom: the consumer's blocking time is a budget the substrate must spend frugally.
+
+## Receipts
+
+- **PTXprint-MCP v1.2 typesetting.** `submit_typeset` / `get_job_status` / `cancel_job` triad. Worker → `ctx.waitUntil(fetch())` → Container → DO state. 30-minute jobs do not block the consumer's MCP session at any point.
+- **AMS hosted /mcp.** `ams_send` returns on wire-accept, not peer-receive. `ams_recv` is the explicit poll path with a 5–10s long-poll cap. `ams_leave` is the cancellation path. Same shape.
+- *(Future receipts: each compliant server adds one row — server, action tool, status tool, cancel tool, observed median submit latency.)*
diff --git a/docs/promotions/P0005-async-by-default-for-long-running-tools.md b/docs/promotions/P0005-async-by-default-for-long-running-tools.md
index 5ec1ddf..1e7e354 100644
--- a/docs/promotions/P0005-async-by-default-for-long-running-tools.md
+++ b/docs/promotions/P0005-async-by-default-for-long-running-tools.md
@@ -6,8 +6,8 @@ exposure: nav
 tier: 3
 voice: neutral
 stability: evolving
-tags: ["promotions", "proposed", "mcp-server", "async", "long-running", "job-id", "polling", "latency"]
-promotion_status: proposed
+tags: ["promotions", "accepted", "mcp-server", "async", "long-running", "job-id", "polling", "latency"]
+promotion_status: accepted
 ---
 
 # P0005: Async by Default — Long-Running MCP Tools Return an Identifier, Never Block
@@ -132,16 +132,14 @@ The principle is distinct from `partial-data-with-transparency-and-background-wa
 
 ## Status
 
-`proposed`
+`accepted` (2026-05-05)
 
 ## Review Notes
 
-(To be filled during review)
-
-- **Reviewer**:
-- **Decision**:
-- **Date**:
-- **Notes**:
+- **Reviewer**: klappy (operator)
+- **Decision**: `accepted`
+- **Date**: 2026-05-05
+- **Notes**: Last of the 8-proposal sweep (P0001 + P0003–P0009 behind the just-merged P0002 chain). Created `canon/principles/async-by-default-for-long-running-tools.md` as a tier-2 principle doc. Action-side complement to `partial-data-with-transparency-and-background-warm` (which is the read-side rule). Codifies the three-tool triad (`<verb>`, `get_<verb>_status`, `cancel_<verb>`) and the four latency budgets. Receipts: PTXprint v1.2 typesetting + AMS hosted /mcp.
 
 ## Execution Record