Phase 1 run-control semantics and run_state events

docs/api/PROTOCOL.md

@@ -69,7 +69,7 @@ sequenceDiagram
   end
 
   G->>A: process(message) in that session
-  A-->>G: streaming events (content/tool_start/tool_end/context_warning)
+  A-->>G: streaming events (content/tool_start/tool_end/context_warning/run_state)
   G-->>C: events + final done
 
   C->>G: agent.cancel {connectionId}
@@ -1028,6 +1028,18 @@ Send a message to the agent and stream response.
 }
 ```
 
+`run_state` event:
+```json
+{
+  "id": 7,
+  "event": "run_state",
+  "data": {
+    "state": "complete",
+    "timestamp": 1730140800000
+  }
+}
+```
+
 `done` event:
 ```json
 {
@@ -1550,6 +1562,21 @@ Proactive context pressure signal emitted by `agent.send` before `done`.
 }
 ```
 
+#### `run_state`
+
+Run lifecycle transition emitted during `agent.send` processing.
+
+```json
+{
+  "id": 1,
+  "event": "run_state",
+  "data": {
+    "state": "start",
+    "timestamp": 1730140800000
+  }
+}
+```
+
 #### `done`
 
 Agent processing complete (final response).
@@ -1715,6 +1742,9 @@ class FlynnClient {
       case 'context_warning':
         console.warn('Context warning:', data.level, data.message);
         break;
+      case 'run_state':
+        console.log('Run state:', data.state, data.timestamp);
+        break;
       case 'done':
         console.log('Done:', data.content);
         break;