docs(architecture): explain gateway session mapping and per-session queueing

docs/README.md

@@ -6,6 +6,7 @@ This documentation is written to be useful to both humans and AI agents. If you
 
 1. Architecture overview (agent-oriented)
    - `docs/architecture/AGENT_DIAGRAM.md`
+   - `docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md`
    - `docs/architecture/TYPESCRIPT_MAP.md`
    - `docs/architecture/SYMBOL_INDEX.md`
    - `docs/architecture/CONTRIBUTOR_MAP.md`
@@ -37,4 +38,3 @@ flowchart TD
   NA --> TP[ToolPolicy + ToolRegistry]
   TP --> TE[ToolExecutor\nhooks + enforcement + audit]
 ```
-

docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md

@@ -0,0 +1,100 @@
+# Gateway Sessions and Queueing (Agent Execution Model)
+
+This document explains how the gateway maps WebSocket clients onto durable sessions, and how work is serialised per session so agent execution stays coherent under concurrent requests.
+
+If you only want the protocol surface, see `docs/api/PROTOCOL.md`.
+
+## Key Ideas
+
+- A WebSocket client gets a `connectionId`.
+- Each connection is attached to a `sessionId`.
+- Agent work is queued per `sessionId` (FIFO), not per connection.
+- Sessions persist in SQLite via `SessionManager` even if clients disconnect.
+
+## Component Map
+
+```mermaid
+flowchart LR
+  subgraph GW[Gateway Process]
+    WS[WebSocket connection\n(connectionId)]
+    GS[GatewayServer]
+    LQ[LaneQueue\nper-session FIFO]
+    SB[SessionBridge\nconnectionId -> sessionId -> AgentOrchestrator]
+  end
+
+  subgraph CORE[Flynn Core]
+    SM[SessionManager\nin-memory cache + SQLite]
+    SS[SessionStore\nSQLite tables]
+    AO[AgentOrchestrator]
+  end
+
+  WS --> GS
+  GS --> LQ
+  GS --> SB
+
+  SB --> AO
+  SB --> SM
+  SM --> SS
+```
+
+## Session IDs (What Actually Gets Stored)
+
+The durable session ID stored by `SessionManager` is:
+
+`<frontend>:<userId>`
+
+For the gateway:
+
+- `SessionBridge.connect()` assigns a `connectionId` (UUID).
+- It defaults the connection's `sessionId` to `ws:<connectionId>`.
+- It then calls `SessionManager.getSession('ws', sessionId)`.
+
+That means gateway sessions are stored as:
+
+- `ws:ws:<connectionId>`
+
+This is expected: the gateway adds its own namespace, and the session manager namespaces again by frontend.
+
+Key files:
+
+- `src/gateway/session-bridge.ts`
+- `src/session/manager.ts`
+
+## Per-Session FIFO Queueing (LaneQueue)
+
+`agent.send` uses a lane ID derived from the session:
+
+- lane = `SessionBridge.getSessionId(connectionId)` (preferred)
+- fallback lane = `connectionId` (only if session lookup fails)
+
+Within a lane:
+
+- Only one request executes at a time.
+- Later requests queue (FIFO) and start after the active request finishes.
+
+Across lanes:
+
+- Independent sessions run in parallel.
+
+Key files:
+
+- `src/gateway/lane-queue.ts`
+- `src/gateway/handlers/agent.ts`
+
+## Cancellation Semantics
+
+`agent.cancel` performs two separate actions:
+
+1. Cancels any queued (not-yet-started) work in the lane (`LaneQueue.cancel(laneId)`).
+2. Requests cancellation of the active agent operation (`AgentOrchestrator.cancel()` via `SessionBridge.cancel()`).
+
+Important:
+
+- Cancellation is best-effort for the currently running work: it stops at the next safe point in the agent loop.
+- Queued work is deterministically rejected.
+
+Key files:
+
+- `src/gateway/handlers/agent.ts`
+- `src/backends/native/orchestrator.ts`
+

docs/plans/state.json

@@ -9,6 +9,11 @@
       "date": "2026-02-15",
       "summary": "Docs gap pass: added docs/README.md as a start-here index and expanded docs/api/PROTOCOL.md with a precise Mermaid diagram explaining per-session lane queueing and cancellation semantics for agent.send/agent.cancel."
     },
+    "docs-gateway-sessions-and-queue": {
+      "status": "completed",
+      "date": "2026-02-15",
+      "summary": "Added docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md to document how gateway connectionIds map to durable sessionIds, how per-session FIFO lane queueing works, and how agent.cancel behaves."
+    },
     "openclaw-gap-roadmap": {
       "file": "2026-02-15-openclaw-gap-roadmap.md",
       "status": "planned",