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/user-instance.ts

@@ -190,6 +190,10 @@ async function handleCommand(cmd: SidecarCommand, reply: ReplyFn) {
       reply({ type: 'claude:interrupted', id: cmd.id });
       break;
 
+    case 'claude:is-generating':
+      reply({ type: 'claude:generating', id: cmd.id, generating: claudeManager.isSessionGenerating(cmd.sessionKey) });
+      break;
+
     case 'claude:clear-session':
       claudeManager.clearSession(cmd.sessionKey);
       sessionLog.drop(cmd.sessionKey);