feat: normalized external-agent status (#10 scoped) (v2.7.6)

Scoped half of boocode_code_review_v2 §1 #10 — publish the agent status
BooCoder already observes (the config-injection notify-hook is the documented
follow-on, clean-room from superset ELv2).

- agent_status_updated WS frame (working|blocked|idle|error), server+web parity.
- Published from the dispatcher's turn boundaries (warm-acp/opencode/sdk/pty:
  working at start, idle/error at end) + the permission flow (blocked/working).
  Best-effort, never breaks a turn.
- Clean-room normalizeAgentEvent helper (superset's vendor-event -> Start/blocked
  /Stop collapse, event names as facts) + 25 tests — reused by the follow-on.
- AgentComposerBar status dot (distinct from the WS-liveness dot), tracked per
  (chat,agent) by a useAgentStatus map in CoderPane.

Built by 2 parallel agents vs a pinned frame contract. Server 545 + coder 294
tests passing (25 new); web tsc + builds clean; ws-frames parity green. Clears
the actionable review backlog (#1/#3/#4/#6-#12). Builds on v2.7.5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/coder/src/services/agent-status-publish.ts

@@ -0,0 +1,55 @@
+/**
+ * agent-status-publish (#10) — builds + publishes the `agent_status_updated`
+ * WS frame on the per-session channel (the same channel CoderPane subscribes to).
+ *
+ * Kept separate from normalize-agent-status.ts so that module stays a pure,
+ * broker-free helper (trivially unit-testable; reused by the config-injection
+ * follow-on). The frame contract is pinned in apps/server/src/types/ws-frames.ts
+ * (`AgentStatusUpdatedFrame`) and mirrored byte-identical in apps/web.
+ */
+import type { Broker } from '@boocode/server/broker';
+import type { WsFrame } from '@boocode/server/ws-frames';
+import type { AgentStatus } from './normalize-agent-status.js';
+
+// The exact slice of Broker we need — accepting just the bound method keeps call
+// sites flexible (pass `broker.publishFrame.bind(broker)` or, since the broker's
+// publishFrame doesn't read `this`, `broker.publishFrame` directly).
+type PublishFrame = Broker['publishFrame'];
+
+/**
+ * Best-effort publish of a normalized agent status. The broker's publishFrame
+ * already fail-closes (validates + logs + drops on bad input, never throws), but
+ * we additionally swallow any unexpected error so a publish can NEVER break the
+ * turn it's reporting on.
+ *
+ * @param publishFrame  the session channel publisher (broker.publishFrame)
+ * @param sessionId     WS subscription channel (CoderPane subscribes per-session)
+ * @param chatId        the (chat) half of the (chat, agent) status key
+ * @param agent         the (agent) half of the key
+ * @param status        normalized lifecycle status
+ * @param reason        free-form discriminator (turn_start / turn_complete / …)
+ * @param at            ISO timestamp; defaults to now
+ */
+export function publishAgentStatus(
+  publishFrame: PublishFrame,
+  sessionId: string,
+  chatId: string,
+  agent: string,
+  status: AgentStatus,
+  reason?: string,
+  at: string = new Date().toISOString(),
+): void {
+  try {
+    const frame: WsFrame = {
+      type: 'agent_status_updated',
+      chat_id: chatId,
+      agent,
+      status,
+      ...(reason ? { reason } : {}),
+      at,
+    };
+    publishFrame(sessionId, frame);
+  } catch {
+    // never let a status publish break the turn — best-effort only.
+  }
+}