end a turn whose agent has gone

restarting officer-agent takes every persistent session with it and nothing
downstream notices: the browser's socket is healthy, officer's subscription is
a bus filter, and there is simply never another event. the spinner ran forever
and a refresh didn't help, because the transcript has no ending to read.

keyed off the agent *registering*, not disconnecting — a disconnect fires on
every `pm2 restart officer`, when the turn is fine. a registration socket dies
with its process, so an agent appearing on it is a new one. covers the sitting
tab; the reconnect path covers the rest, with the client now sending its belief
that a turn is in flight and officer checking it against the agent over a new
claude:is-generating. the check fails toward alive.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/sidecar/claude/claude-manager.ts

@@ -379,3 +379,15 @@ export function clearSession(sessionKey: string): void {
 export function getActiveSessionKeys(): string[] {
   return Array.from(sessions.keys());
 }
+
+/**
+ * Is a turn actually in flight for this session, right now, in this process?
+ *
+ * This is the ground truth a reconnecting browser has no way to work out for itself. Officer's own view
+ * dies with `pm2 restart officer` while the turn keeps running here, so "officer doesn't remember" means
+ * nothing — and if *this* process was the one that restarted, the session is simply absent and the turn
+ * it was running is gone, however alive the client still believes it to be.
+ */
+export function isSessionGenerating(sessionKey: string): boolean {
+  return sessions.get(sessionKey)?.isGenerating ?? false;
+}