feat(transport): CLI endpoints + conversation.open broadcast (Wave 2)

transport-http: GET /conversations (list with ?q= prefix filter),
GET /conversations/:id/last (blocks until turn settles, returns last AI
text), POST /conversations/:id/open (emits conversationOpened hook),
PUT /conversations/:id/title (set title). emit threaded from host.emit.
extractLastAssistantText pure helper. 21 new tests (166 total).

transport-ws: subscribes to conversationOpened hook, broadcasts
ConversationOpenMessage to all connected WS clients. 2 new tests.

session-orchestrator: conversationOpened hook descriptor (exported).

2 files changed, 16 insertions, 0 deletions

diff --git a/packages/session-orchestrator/src/index.ts b/packages/session-orchestrator/src/index.ts
index afec2b4..3d8ad18 100644
--- a/packages/session-orchestrator/src/index.ts
+++ b/packages/session-orchestrator/src/index.ts
@@ -1,8 +1,10 @@
 export { extension, manifest } from "./extension.js";
 export {
 	type ConversationClosedPayload,
+	type ConversationOpenedPayload,
 	cacheWarmHandle,
 	conversationClosed,
+	conversationOpened,
 	createSessionOrchestrator,
 	createWarmService,
 	type EnqueueInput,
diff --git a/packages/session-orchestrator/src/orchestrator.ts b/packages/session-orchestrator/src/orchestrator.ts
index 3a74c2d..82ca59e 100644
--- a/packages/session-orchestrator/src/orchestrator.ts
+++ b/packages/session-orchestrator/src/orchestrator.ts
@@ -97,6 +97,20 @@ export interface ConversationClosedPayload {
 export const conversationClosed: EventHookDescriptor<ConversationClosedPayload> =
 	defineEventHook<ConversationClosedPayload>("session-orchestrator/conversation-closed");
 
+/** Payload for the conversationOpened bus event. */
+export interface ConversationOpenedPayload {
+	readonly conversationId: string;
+}
+
+/**
+ * Fired when a client requests to "open" a conversation (e.g. the CLI `--open`
+ * flag). Transport-ws subscribes and broadcasts a `conversation.open` WS
+ * message to all connected frontend clients. The frontend decides whether to
+ * open/focus a tab — the backend just signals.
+ */
+export const conversationOpened: EventHookDescriptor<ConversationOpenedPayload> =
+	defineEventHook<ConversationOpenedPayload>("session-orchestrator/conversation-opened");
+
 /** Payload for the warmCompleted bus event. */
 export interface WarmCompletedPayload {
 	readonly conversationId: string;