docs(rfc): Add orchestrator workflow diagram and controller summary

doc/rfc/index.md

@@ -5,3 +5,4 @@ Design documents and technical proposals for SubmitQueue.
 ## Index
 
 - [SQL-Based Distributed Queue](sql-queue-rfc.md) - MySQL-based distributed message queue with partition leasing and at-least-once delivery
+- [Orchestrator Workflow](workflow.md) - Queue-driven controller pipeline from gateway entry through batching, scoring, build, merge, and conclude

doc/rfc/workflow.md

@@ -0,0 +1,82 @@
+# Orchestrator Workflow
+
+The orchestrator processes land requests through a queue-driven pipeline of small, single-purpose controllers. The gateway accepts a request over RPC and hands it off asynchronously; from there each controller consumes one topic, advances the request or batch, and publishes to the next topic. Most hops carry only an ID — the controller fetches the entity from storage — while a few entry points (`start`, `buildsignal`, `log`) carry the full payload because there is no row to fetch yet.
+
+The pipeline has two cycles: `speculate → build → buildsignal → speculate` (CI feedback loop) and `merge → speculate` (advance the next batch). `conclude` is the only stage that transitions a request to a terminal state; `log` is an append-only sink that any controller can publish to via `core/request.PublishLog`.
+
+## Diagram
+
+```
+                    ┌──────────────────────────────────┐
+                    │ gateway:Land  (RPC entry)        │
+                    │ Accept, mint ID, hand off async  │
+                    └────────────────┬─────────────────┘
+                                     │ LandRequest
+                                     ▼
+   ┌──────────────────────┐    ┌──────────────────────────────────┐
+   │ log  (terminal sink) │◄───│ start                            │
+   │ Append RequestLog    │    │ Persist Request, emit Started    │
+   └──────────────────────┘    └────────────────┬─────────────────┘
+              ▲                                 │ RequestID
+              │                                 ▼
+              │                 ┌──────────────────────────────────┐
+              │                 │ validate                         │
+              │                 │ Check mergeability + change meta │
+              │                 └────────────────┬─────────────────┘
+              │                                  │ RequestID
+              │                                  ▼
+              │                 ┌──────────────────────────────────┐
+              │                 │ batch                            │
+              │                 │ Group request into a Batch       │
+              │                 └────────────────┬─────────────────┘
+              │                                  │ BatchID
+              │                                  ▼
+              │                 ┌──────────────────────────────────┐
+              ├─────────────────│ score                            │
+              │   RequestLog×N  │ Score the batch, persist score   │
+              │                 └────────────────┬─────────────────┘
+              │                                  │ BatchID
+              │                                  ▼
+              │            ┌──────────────────────────────────┐
+              │       ┌───►│ speculate  (stub)                │◄────┐
+              │       │    │ Decide CI verify vs. land        │     │
+              │       │    └──────┬─────────────────┬─────────┘     │
+              │       │  BatchID  │                 │ BatchID       │
+              │       │           ▼                 ▼               │
+              │       │  ┌──────────────────┐  ┌──────────────────┐ │
+              │       │  │ build            │  │ merge            │ │
+              │       │  │ Trigger CI build │  │ Merge + advance  │─┤
+              │       │  └────────┬─────────┘  └────────┬─────────┘ │
+              │       │   Build   │                     │ BatchID   │
+              │       │           ▼                     │           │
+              │       │  ┌──────────────────┐           │           │
+              │       └──│ buildsignal      │           │           │
+              │  BatchID │ Feed CI result   │           │           │
+              │          │ back to spec.    │           │           │
+              │          └──────────────────┘           │           │
+              │                  ▲                      │ BatchID   │
+              │                  │ Build (ext. CI)      ▼           │
+              │                  │            ┌──────────────────┐  │
+              │                  │            │ conclude         │  │
+              │                  │            │ Map batch state  │  │
+              │                  │            │ → request state  │  │
+              │                  │            └──────────────────┘  │
+              │                  │                                  │
+              └─── any controller via core/request.PublishLog ──────┘
+```
+
+## Per-controller summary
+
+| Controller | In | Out | One-line role |
+|---|---|---|---|
+| **gateway/Land** | RPC | start | Accept request, mint ID, log Accepted, hand off async |
+| **start** | LandRequest | validate, log | Persist Request and emit Started log |
+| **validate** | RequestID | batch | Check mergeability and fetch change metadata |
+| **batch** | RequestID | score | Group request into a Batch with dependencies |
+| **score** | BatchID | speculate, log | Score the batch (∏ per-request scores), persist score |
+| **speculate** | BatchID | build, merge | (stub) Decide whether to verify via CI or land |
+| **build** | BatchID | buildsignal | Trigger CI build for the batch |
+| **buildsignal** | Build | speculate | Feed CI result back into speculation |
+| **merge** | BatchID | conclude, speculate | Merge the batch and advance the queue |
+| **conclude** | BatchID | — | Map terminal batch state to request state |
+| **log** | RequestLog | — | Append-only sink for request log events |