Gate inbox delivery on worker-side steer ACK

Replace the fire-and-forget steer with a correlated ACK round-trip so main
only marks an inbox row delivered once the worker confirms the message
landed on the live Agent. Steer against a run that is still in the
`preparing` window or has already started `closing` now falls back to the
wake + inbox projection path instead of being silently dropped.

Worker publishes `run-agent-state` transitions at Agent construction and
teardown; main tracks these on `ActiveRunContext.state` and refuses to
steer runs that are not `agent_active`. A rejected or timed-out ACK
triggers `wakeAgentIfPossible` so the next `prepareRun` replays the row.

src/main/worker/worker-runner.ts

@@ -28,8 +28,10 @@ interface RunnerDeps {
  *  - Builds an `Agent` via `createPiAgent` with the full Pi contract.
  *  - Streams every pi `AgentEvent` into the worker → main pipe.
  *  - Persists each `message_end` message through `persistMessage` RPC.
- *  - Exposes `steer` / `followUp` to the worker entry so mid-run
- *    injections from main land on the in-process Agent instance.
+ *  - Exposes `steer` to the worker entry so mid-run injections from
+ *    main land on the in-process Agent instance.
+ *  - Publishes `run-agent-state` transitions so main can tell whether
+ *    an active run is actually ready to accept steer messages.
  */
 export class WorkerRunner {
   private readonly abortControllers = new Map<string, AbortController>();
@@ -43,7 +45,15 @@ export class WorkerRunner {
     if (controller) controller.abort();
   }
 
-  /** Enqueue a steering message onto the active Agent for this run. */
+  /**
+   * Enqueue a steering message onto the active Agent for this run. Returns
+   * true iff the Agent instance exists in `activeAgents` and the message
+   * was appended to its steering queue. A false return means the run has
+   * either not finished construction (pre-`agent_active`) or has already
+   * torn down (post-`closing`); callers must treat the steer as rejected
+   * so main can hold the inbox `delivered_at` write and fall back to the
+   * inbox + wake path instead.
+   */
   steer(runId: string, message: AgentMessage): boolean {
     const agent = this.activeAgents.get(runId);
     if (!agent) return false;
@@ -51,14 +61,6 @@ export class WorkerRunner {
     return true;
   }
 
-  /** Enqueue a follow-up message onto the active Agent for this run. */
-  followUp(runId: string, message: AgentMessage): boolean {
-    const agent = this.activeAgents.get(runId);
-    if (!agent) return false;
-    agent.followUp(message);
-    return true;
-  }
-
   /**
    * Aborts every in-flight run and returns a promise that resolves once
    * each `run()` has settled (success, failure, or abort). Callers (the
@@ -150,6 +152,7 @@ export class WorkerRunner {
           rpc,
         });
         this.activeAgents.set(job.runId, agent);
+        post({ type: "run-agent-state", runId: job.runId, state: "agent_active" });
 
         const unsubscribe = agent.subscribe(async (event) => {
           const timestamp = new Date().toISOString();
@@ -192,6 +195,7 @@ export class WorkerRunner {
           abortController.signal.addEventListener("abort", () => agent.abort(), { once: true });
           await runPromise;
         } finally {
+          post({ type: "run-agent-state", runId: job.runId, state: "closing" });
           unsubscribe();
           this.activeAgents.delete(job.runId);
         }