fix: prevent daemon silent death from SIGHUP + unhandled errors

Root cause: registerSignalHandlers() handled SIGTERM/SIGINT but not
SIGHUP. When the parent hook process exits, the kernel sends SIGHUP
to the daemon, causing immediate termination (default signal action).

Belt-and-suspenders fix:
1. SIGHUP handler: ignore in daemon mode, graceful shutdown otherwise
2. setsid: spawn daemon in new session on Linux (prevents SIGHUP delivery)
3. Global unhandledRejection/uncaughtException guards in daemon mode

src/services/infrastructure/ProcessManager.ts

@@ -384,7 +384,27 @@ export function spawnDaemon(
     }
   }
 
-  // Unix: standard detached spawn
+  // Unix: Use setsid to create a new session, fully detaching from the
+  // controlling terminal. This prevents SIGHUP from reaching the daemon
+  // even if the in-process SIGHUP handler somehow fails (belt-and-suspenders).
+  // Fall back to standard detached spawn if setsid is not available.
+  const setsidPath = '/usr/bin/setsid';
+  if (existsSync(setsidPath)) {
+    const child = spawn(setsidPath, [process.execPath, scriptPath, '--daemon'], {
+      detached: true,
+      stdio: 'ignore',
+      env
+    });
+
+    if (child.pid === undefined) {
+      return undefined;
+    }
+
+    child.unref();
+    return child.pid;
+  }
+
+  // Fallback: standard detached spawn (macOS, systems without setsid)
   const child = spawn(process.execPath, [scriptPath, '--daemon'], {
     detached: true,
     stdio: 'ignore',

src/services/worker-service.ts

@@ -231,6 +231,22 @@ export class WorkerService {
       this.isShuttingDown = shutdownRef.value;
       handler('SIGINT');
     });
+
+    // SIGHUP: sent by kernel when controlling terminal closes.
+    // Daemon mode: ignore it (survive parent shell exit).
+    // Interactive mode: treat like SIGTERM (graceful shutdown).
+    if (process.platform !== 'win32') {
+      if (process.argv.includes('--daemon')) {
+        process.on('SIGHUP', () => {
+          logger.debug('SYSTEM', 'Ignoring SIGHUP in daemon mode');
+        });
+      } else {
+        process.on('SIGHUP', () => {
+          this.isShuttingDown = shutdownRef.value;
+          handler('SIGHUP');
+        });
+      }
+    }
   }
 
   /**
@@ -971,6 +987,18 @@ async function main() {
 
     case '--daemon':
     default: {
+      // Prevent daemon from dying silently on unhandled errors.
+      // The HTTP server can continue serving even if a background task throws.
+      process.on('unhandledRejection', (reason) => {
+        logger.error('SYSTEM', 'Unhandled rejection in daemon', {
+          reason: reason instanceof Error ? reason.message : String(reason)
+        });
+      });
+      process.on('uncaughtException', (error) => {
+        logger.error('SYSTEM', 'Uncaught exception in daemon', {}, error as Error);
+        // Don't exit — keep the HTTP server running
+      });
+
       const worker = new WorkerService();
       worker.start().catch((error) => {
         logger.failure('SYSTEM', 'Worker failed to start', {}, error as Error);