fix(tui): add hybrid polling safety net to HUD bridge (#1204)

apps/mcp-server/src/tui/events/hud-file-bridge.spec.ts

@@ -30,7 +30,7 @@ describe('HudFileBridge', () => {
 
   it('emits MODE_CHANGED when currentMode changes in file', async () => {
     writeHudState(hudFile, { currentMode: 'PLAN' });
-    bridge = new HudFileBridge(eventBus, hudFile, { debounceMs: 10 });
+    bridge = new HudFileBridge(eventBus, hudFile, { debounceMs: 10, pollIntervalMs: 50 });
     bridge.start();
 
     const modeChanges: Array<{ from: string | null; to: string }> = [];
@@ -61,7 +61,7 @@ describe('HudFileBridge', () => {
 
   it('emits AGENT_ACTIVATED when activeAgent changes', async () => {
     writeHudState(hudFile, { currentMode: 'PLAN', activeAgent: null });
-    bridge = new HudFileBridge(eventBus, hudFile, { debounceMs: 10 });
+    bridge = new HudFileBridge(eventBus, hudFile, { debounceMs: 10, pollIntervalMs: 50 });
     bridge.start();
 
     const activations: unknown[] = [];
@@ -107,13 +107,16 @@ describe('HudFileBridge', () => {
     const modeChanges: Array<{ from: string | null; to: string }> = [];
     eventBus.on(TUI_EVENTS.MODE_CHANGED, p => modeChanges.push(p));
 
-    // Simulate watcher error to trigger polling fallback
-    // Access internal watcher and emit error
+    // Simulate watcher error — polling is already running (hybrid mode)
     const watcher = (bridge as unknown as { watcher: fs.FSWatcher | null }).watcher;
     expect(watcher).not.toBeNull();
     watcher!.emit('error', new Error('EPERM'));
 
-    // Write new state — polling should detect the change
+    // Watcher should be cleaned up after error
+    const bridgeInternal = bridge as unknown as { watcher: fs.FSWatcher | null };
+    expect(bridgeInternal.watcher).toBeNull();
+
+    // Write new state — polling safety net should detect the change
     await sleep(100);
     writeHudState(hudFile, { currentMode: 'ACT' });
     await sleep(300);
@@ -122,6 +125,31 @@ describe('HudFileBridge', () => {
     expect(modeChanges[modeChanges.length - 1]).toEqual({ from: 'PLAN', to: 'ACT' });
   });
 
+  it('runs hybrid mode — both watch and poll active simultaneously', async () => {
+    writeHudState(hudFile, { currentMode: 'PLAN' });
+    bridge = new HudFileBridge(eventBus, hudFile, { debounceMs: 10, pollIntervalMs: 50 });
+    bridge.start();
+
+    const bridgeInternal = bridge as unknown as {
+      watcher: fs.FSWatcher | null;
+      pollInterval: ReturnType<typeof setInterval> | null;
+    };
+
+    // Both watcher and polling should be active (hybrid mode)
+    expect(bridgeInternal.watcher).not.toBeNull();
+    expect(bridgeInternal.pollInterval).not.toBeNull();
+
+    // Polling alone should detect changes even if fs.watch is silent
+    const modeChanges: Array<{ from: string | null; to: string }> = [];
+    eventBus.on(TUI_EVENTS.MODE_CHANGED, p => modeChanges.push(p));
+
+    writeHudState(hudFile, { currentMode: 'EVAL' });
+    await sleep(300);
+
+    expect(modeChanges.length).toBeGreaterThanOrEqual(1);
+    expect(modeChanges[modeChanges.length - 1]).toEqual({ from: 'PLAN', to: 'EVAL' });
+  });
+
   it('handles malformed JSON gracefully', async () => {
     writeHudState(hudFile, { currentMode: 'PLAN' });
     bridge = new HudFileBridge(eventBus, hudFile, { debounceMs: 10 });

apps/mcp-server/src/tui/events/hud-file-bridge.ts

@@ -15,7 +15,7 @@ const VALID_MODES = new Set(['PLAN', 'ACT', 'EVAL', 'AUTO']);
 export interface HudFileBridgeOptions {
   /** Debounce interval in ms (default: 150) */
   debounceMs?: number;
-  /** Polling interval in ms when fs.watch fails (default: 1000) */
+  /** Polling interval in ms for hybrid safety-net polling (default: 200) */
   pollIntervalMs?: number;
 }
 
@@ -41,7 +41,7 @@ export class HudFileBridge {
     this.eventBus = eventBus;
     this.filePath = filePath;
     this.debounceMs = options?.debounceMs ?? 150;
-    this.pollIntervalMs = options?.pollIntervalMs ?? 1000;
+    this.pollIntervalMs = options?.pollIntervalMs ?? 200;
   }
 
   start(): void {
@@ -61,11 +61,13 @@ export class HudFileBridge {
         if (!filename || filename === basename) this.scheduleProcess();
       });
       this.watcher.on('error', () => {
-        // Directory deleted or inaccessible — fall back to polling
+        // Watcher failed — close it; polling is already running as safety net
         this.watcher?.close();
         this.watcher = null;
-        this.startPollingFallback();
+        process.stderr.write('[codingbuddy] fs.watch failed, polling safety net active\n');
       });
+      // Hybrid mode: run polling alongside fs.watch as a silent safety net
+      this.startPollingFallback(true);
     } catch {
       // Directory doesn't exist yet — poll until it appears
       this.pollUntilExists();
@@ -135,9 +137,11 @@ export class HudFileBridge {
     }
   }
 
-  private startPollingFallback(): void {
+  private startPollingFallback(silent: boolean = false): void {
     if (this.stopped || this.pollInterval) return;
-    process.stderr.write('[codingbuddy] fs.watch failed, falling back to polling\n');
+    if (!silent) {
+      process.stderr.write('[codingbuddy] fs.watch failed, falling back to polling\n');
+    }
     try {
       const stat = fs.statSync(this.filePath);
       this.lastMtimeMs = stat.mtimeMs;