v1.40.0.2 fix(browse): Cmd+Q on managed Chromium stops triggering supervisor respawn

Three browser.on('disconnected') handlers in browse/src/browser-manager.ts
(launch, launchHeaded, handoff) each exited with a non-zero code on every
disconnect, regardless of cause. Process supervisors that consume our exit
code (gbrowser's gbd HealthMonitor in cmd/gbd/health.go) treated user
Cmd+Q identical to a Chromium crash and respawned with exponential
backoff, so the visible browser kept reappearing after the user closed it.

Add resolveDisconnectCause(browser) that reads the underlying ChildProcess
exitCode + signalCode (waiting up to 1s for the exit event if the
disconnected event fired first). Exit code 0 + no signal = clean user
quit; anything else = crash, signal-kill, or OOM.

Wire the resolver into all three disconnect handlers:
- launch() (headless): clean → exit 0, crash → exit 1 (was always 1)
- launchHeaded() (headed): clean → exit 0, crash → exit 2 (was always 2)
  onDisconnect() cleanup callback still runs in both cases.
- handoff() (re-launch): same as launch() via the helper.

Preserve the per-path crash codes (1 vs 2) so any supervisor that
differentiated headed vs headless crashes keeps working.

Seven new unit tests in browse-manager-unit.test.ts cover the resolver
across already-exited, signal-killed (SIGSEGV / SIGKILL), async exits,
and null-browser inputs.

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

browse/test/browser-manager-unit.test.ts

@@ -1,3 +1,4 @@
+import { EventEmitter } from 'node:events';
 import { afterEach, beforeEach, describe, it, expect } from 'bun:test';
 
 // ─── BrowserManager basic unit tests ─────────────────────────────
@@ -90,3 +91,75 @@ describe('shouldEnableChromiumSandbox', () => {
     expect(shouldEnableChromiumSandbox()).toBe(false);
   });
 });
+
+// ─── resolveDisconnectCause ──────────────────────────────────────
+//
+// Pinning the clean-vs-crash distinction matters because gbd's
+// HealthMonitor consumes our exit code (0 = don't restart, !=0 =
+// restart). A regression here brings back the "Cmd+Q makes the browser
+// keep coming back" UX bug.
+
+function makeFakeBrowser(opts: {
+  exitCode: number | null;
+  signalCode: NodeJS.Signals | null;
+  /** ms before emitting 'exit'; default = already exited at construction */
+  exitDelay?: number;
+}): { process(): { exitCode: number | null; signalCode: NodeJS.Signals | null; once: EventEmitter['once'] } } {
+  const ee = new EventEmitter();
+  const state = {
+    exitCode: opts.exitDelay != null ? null : opts.exitCode,
+    signalCode: opts.exitDelay != null ? null : opts.signalCode,
+    once: ee.once.bind(ee),
+  };
+  if (opts.exitDelay != null) {
+    setTimeout(() => {
+      state.exitCode = opts.exitCode;
+      state.signalCode = opts.signalCode;
+      ee.emit('exit', opts.exitCode, opts.signalCode);
+    }, opts.exitDelay);
+  }
+  return { process: () => state };
+}
+
+describe('resolveDisconnectCause', () => {
+  it('clean: process already exited with code 0', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    const fake = makeFakeBrowser({ exitCode: 0, signalCode: null });
+    expect(await resolveDisconnectCause(fake as never)).toBe('clean');
+  });
+
+  it('crash: non-zero exit code', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    const fake = makeFakeBrowser({ exitCode: 1, signalCode: null });
+    expect(await resolveDisconnectCause(fake as never)).toBe('crash');
+  });
+
+  it('crash: SIGSEGV', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    const fake = makeFakeBrowser({ exitCode: null, signalCode: 'SIGSEGV' });
+    expect(await resolveDisconnectCause(fake as never)).toBe('crash');
+  });
+
+  it('crash: SIGKILL', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    const fake = makeFakeBrowser({ exitCode: null, signalCode: 'SIGKILL' });
+    expect(await resolveDisconnectCause(fake as never)).toBe('crash');
+  });
+
+  it('clean: process exits asynchronously with code 0 within timeout', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    const fake = makeFakeBrowser({ exitCode: 0, signalCode: null, exitDelay: 50 });
+    expect(await resolveDisconnectCause(fake as never)).toBe('clean');
+  });
+
+  it('crash: process exits asynchronously with non-zero code', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    const fake = makeFakeBrowser({ exitCode: 137, signalCode: null, exitDelay: 50 });
+    expect(await resolveDisconnectCause(fake as never)).toBe('crash');
+  });
+
+  it('crash: null browser returns crash (defensive default)', async () => {
+    const { resolveDisconnectCause } = await import('../src/browser-manager');
+    expect(await resolveDisconnectCause(null)).toBe('crash');
+  });
+});