fix: disconnect handler runs full cleanup before exiting

When the user closed the headed browser window, the disconnect handler
in browser-manager.ts called process.exit(2) directly, bypassing the
server's shutdown() function entirely. That meant:

- sidebar-agent daemon kept polling a dead server
- session state wasn't saved
- Chromium profile locks (SingletonLock, SingletonSocket, SingletonCookie)
  weren't cleaned — causing "profile in use" errors on next $B connect
- state file at .gstack/browse.json was left stale

Now the disconnect handler calls onDisconnect(), which server.ts wires
up to shutdown(2). Full cleanup runs first, then the process exits with
code 2 — preserving the existing semantic that distinguishes user-close
(exit 2) from crashes (exit 1).

shutdown() now accepts an optional exitCode parameter (default 0) so
the SIGTERM/SIGINT paths and the disconnect path can share cleanup code
while preserving their distinct exit codes.

Surfaced by Codex during /plan-eng-review of the watchdog fix.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

browse/src/browser-manager.ts

@@ -72,6 +72,11 @@ export class BrowserManager {
   private connectionMode: 'launched' | 'headed' = 'launched';
   private intentionalDisconnect = false;
 
+  // Called when the headed browser disconnects without intentional teardown
+  // (user closed the window). Wired up by server.ts to run full cleanup
+  // (sidebar-agent, state file, profile locks) before exiting with code 2.
+  public onDisconnect: (() => void) | null = null;
+
   getConnectionMode(): 'launched' | 'headed' { return this.connectionMode; }
 
   // ─── Watch Mode Methods ─────────────────────────────────
@@ -467,13 +472,20 @@ export class BrowserManager {
       await this.newTab();
     }
 
-    // Browser disconnect handler — exit code 2 distinguishes from crashes (1)
+    // Browser disconnect handler — exit code 2 distinguishes from crashes (1).
+    // Calls onDisconnect() to trigger full shutdown (kill sidebar-agent, save
+    // session, clean profile locks + state file) before exit. Falls back to
+    // direct process.exit(2) if no callback is wired up.
     if (this.browser) {
       this.browser.on('disconnected', () => {
         if (this.intentionalDisconnect) return;
         console.error('[browse] Real browser disconnected (user closed or crashed).');
         console.error('[browse] Run `$B connect` to reconnect.');
-        process.exit(2);
+        if (this.onDisconnect) {
+          this.onDisconnect();
+        } else {
+          process.exit(2);
+        }
       });
     }
 

browse/src/server.ts

@@ -805,6 +805,10 @@ function emitInspectorEvent(event: any): void {
 
 // ─── Server ────────────────────────────────────────────────────
 const browserManager = new BrowserManager();
+// When the user closes the headed browser window, run full cleanup
+// (kill sidebar-agent, save session, remove profile locks, delete state file)
+// before exiting with code 2. Exit code 2 distinguishes user-close from crashes (1).
+browserManager.onDisconnect = () => shutdown(2);
 let isShuttingDown = false;
 
 // Test if a port is available by binding and immediately releasing.
@@ -1192,7 +1196,7 @@ async function handleCommand(body: any, tokenInfo?: TokenInfo | null): Promise<R
   });
 }
 
-async function shutdown() {
+async function shutdown(exitCode: number = 0) {
   if (isShuttingDown) return;
   isShuttingDown = true;
 
@@ -1233,7 +1237,7 @@ async function shutdown() {
   // Clean up state file
   safeUnlinkQuiet(config.stateFile);
 
-  process.exit(0);
+  process.exit(exitCode);
 }
 
 // Handle signals