fix(coding-agent): emit session name changes to extensions

packages/coding-agent/docs/extensions.md

@@ -322,6 +322,9 @@ user sends another prompt ◄─────────────────
   ├─► session_start { reason: "fork", previousSessionFile }
   └─► resources_discover { reason: "startup" }
 
+/name or pi.setSessionName()
+  └─► session_info_changed
+
 /compact or auto-compaction
   ├─► session_before_compact (can cancel or customize)
   └─► session_compact
@@ -395,6 +398,17 @@ pi.on("session_start", async (event, ctx) => {
 });
 ```
 
+#### session_info_changed
+
+Fired when the current session display name is set via `/name`, RPC, or `pi.setSessionName()`.
+
+```typescript
+pi.on("session_info_changed", async (event, ctx) => {
+  // event.name - current normalized name, or undefined if cleared
+  ctx.ui.notify(`Session renamed: ${event.name ?? "(none)"}`, "info");
+});
+```
+
 #### session_before_switch
 
 Fired before starting a new session (`/new`) or switching sessions (`/resume`).

packages/coding-agent/src/core/agent-session.ts

@@ -2683,7 +2683,9 @@ export class AgentSession {
 	 */
 	setSessionName(name: string): void {
 		this.sessionManager.appendSessionInfo(name);
-		this._emit({ type: "session_info_changed", name: this.sessionManager.getSessionName() });
+		const event = { type: "session_info_changed", name: this.sessionManager.getSessionName() } as const;
+		this._emit(event);
+		void this._extensionRunner.emit(event);
 	}
 
 	// =========================================================================

packages/coding-agent/src/core/extensions/index.ts

@@ -128,6 +128,7 @@ export type {
 	SessionBeforeTreeResult,
 	SessionCompactEvent,
 	SessionEvent,
+	SessionInfoChangedEvent,
 	SessionShutdownEvent,
 	// Events - Session
 	SessionStartEvent,

packages/coding-agent/src/core/extensions/types.ts

@@ -551,6 +551,13 @@ export interface SessionStartEvent {
 	previousSessionFile?: string;
 }
 
+/** Fired when the current session metadata changes. */
+export interface SessionInfoChangedEvent {
+	type: "session_info_changed";
+	/** Current normalized session name. Undefined when the name is cleared. */
+	name: string | undefined;
+}
+
 /** Fired before switching to another session (can be cancelled) */
 export interface SessionBeforeSwitchEvent {
 	type: "session_before_switch";
@@ -630,6 +637,7 @@ export interface SessionTreeEvent {
 
 export type SessionEvent =
 	| SessionStartEvent
+	| SessionInfoChangedEvent
 	| SessionBeforeSwitchEvent
 	| SessionBeforeForkEvent
 	| SessionBeforeCompactEvent
@@ -1133,6 +1141,7 @@ export interface ExtensionAPI {
 	on(event: "project_trust", handler: ProjectTrustHandler): void;
 	on(event: "resources_discover", handler: ExtensionHandler<ResourcesDiscoverEvent, ResourcesDiscoverResult>): void;
 	on(event: "session_start", handler: ExtensionHandler<SessionStartEvent>): void;
+	on(event: "session_info_changed", handler: ExtensionHandler<SessionInfoChangedEvent>): void;
 	on(
 		event: "session_before_switch",
 		handler: ExtensionHandler<SessionBeforeSwitchEvent, SessionBeforeSwitchResult>,

packages/coding-agent/src/index.ts

@@ -122,6 +122,7 @@ export type {
 	SessionBeforeSwitchEvent,
 	SessionBeforeTreeEvent,
 	SessionCompactEvent,
+	SessionInfoChangedEvent,
 	SessionShutdownEvent,
 	SessionStartEvent,
 	SessionTreeEvent,

packages/coding-agent/test/suite/regressions/3686-session-name-event.test.ts

@@ -37,4 +37,25 @@ describe("regression #3686: session name changes emit an event", () => {
 		expect(harness.sessionManager.getSessionName()).toBe("from extension");
 		expect(harness.eventsOfType("session_info_changed").map((event) => event.name)).toEqual(["from extension"]);
 	});
+
+	it("emits session_info_changed to extensions", async () => {
+		let api: ExtensionAPI | undefined;
+		const events: Array<{ name: string | undefined }> = [];
+		const harness = await createHarness({
+			extensionFactories: [
+				(pi) => {
+					api = pi;
+					pi.on("session_info_changed", (event) => {
+						events.push({ name: event.name });
+					});
+				},
+			],
+		});
+		harnesses.push(harness);
+
+		api?.setSessionName("first");
+		harness.session.setSessionName("second");
+
+		expect(events).toEqual([{ name: "first" }, { name: "second" }]);
+	});
 });