Catch failed startup error from build_daemon (#43598)

packages/flutter_tools/lib/src/build_runner/resident_web_runner.dart

@@ -255,6 +255,15 @@ class ResidentWebRunner extends ResidentRunner {
         'start or was killed by another process.');
     } on SocketException catch (err) {
       throwToolExit(err.toString());
+    } on StateError catch (err) {
+      final String message = err.toString();
+      if (message.contains('Unable to start build daemon')) {
+        throwToolExit(
+          'Failed to start build daemon. The process might have '
+          'exited unexpectedly during startup. Try running the application '
+          'again.');
+      }
+      rethrow;
     } finally {
       if (statusActive) {
         buildStatus.stop();

packages/flutter_tools/test/general.shard/resident_web_runner_test.dart

@@ -658,6 +658,26 @@ void main() {
     await expectation;
   }));
 
+  test('Successfully turns failed startup StateError error into ToolExit', () => testbed.run(() async {
+    _setupMocks();
+    final Completer<DebugConnectionInfo> connectionInfoCompleter = Completer<DebugConnectionInfo>();
+    final Completer<void> unhandledErrorCompleter = Completer<void>();
+    when(mockWebFs.connect(any)).thenAnswer((Invocation _) async {
+      unawaited(unhandledErrorCompleter.future.then((void value) {
+        throw StateError('Unable to start build daemon');
+      }));
+      return ConnectionResult(mockAppConnection, mockDebugConnection);
+    });
+
+    final Future<void> expectation = expectLater(() => residentWebRunner.run(
+      connectionInfoCompleter: connectionInfoCompleter,
+    ), throwsA(isInstanceOf<ToolExit>()));
+
+    unhandledErrorCompleter.complete();
+    await expectation;
+  }));
+
+
   test('Rethrows Exception type', () => testbed.run(() async {
     _setupMocks();
     final Completer<DebugConnectionInfo> connectionInfoCompleter = Completer<DebugConnectionInfo>();