fix(session): isolate event listener failures in agent fan-out

Both `AgentSession.#emit` (session/agent-session.ts) and `Agent.#emit`
(packages/agent/src/agent.ts) iterated listeners with no error isolation.
A synchronous throw in any subscriber aborted the for-loop, so later
subscribers (TUI rendering, ACP bridge, task executor progress,
hindsight) silently missed events. Many listeners — see
`modes/controllers/event-controller.ts:141` and
`modes/controllers/input-controller.ts:576` — are registered as
`async (event) => { await this.handleEvent(event); }`; the returned
Promise was dropped, so any rejection became an unhandled rejection.

Wrap each listener invocation in try/catch and attach a `.catch` to any
returned thenable. Errors are logged via `logger.warn` (already imported
in agent-session.ts) and `console.error` (agent.ts has no logger
dependency, keep it that way).

Test: new `test/session/emit-listener-isolation.test.ts` registers two
listeners on both classes; first listener throws (or returns a rejecting
Promise); asserts the second listener still receives the event AND no
`unhandledRejection` fires. 4 cases (sync+async × Agent+AgentSession).
All fail on current main; all pass with the fix.

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

@@ -1307,10 +1307,25 @@ export class AgentSession {
 
 	/** Emit an event to all listeners */
 	#emit(event: AgentSessionEvent): void {
-		// Copy array before iteration to avoid mutation during iteration
+		// Copy array before iteration to avoid mutation during iteration.
 		const listeners = [...this.#eventListeners];
 		for (const l of listeners) {
-			l(event);
+			try {
+				const result = l(event);
+				// Listener may be an async function whose returned Promise we don't await;
+				// attach a catch so a rejection does not become an unhandled rejection.
+				if (result && typeof (result as Promise<unknown>).then === "function") {
+					(result as Promise<unknown>).catch(err => {
+						logger.warn("AgentSession listener rejected", {
+							error: err instanceof Error ? err.message : String(err),
+						});
+					});
+				}
+			} catch (err) {
+				logger.warn("AgentSession listener threw", {
+					error: err instanceof Error ? err.message : String(err),
+				});
+			}
 		}
 	}