share a generous test I/O timeout constant

The flaky-gate fixes kept hand-tuning magic seconds in each real-I/O
test. Pull them into one Flutter-free constant — ioTimeout (20s) in
test/helpers/timeouts.dart, importable by both the dart-test (pty) and
flutter-test suites — and route the real-external-wait timeouts through
it: PTY output (session + registry), and fs-watcher events (timeout +
poll ceiling). Tune in one place instead of scattering durations.

The ipc socket round-trip timeouts (2s) are left as-is — they haven't
flaked and local sockets respond in ms; they can adopt the constant
later if needed.

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

test/files/watcher_test.dart

@@ -8,6 +8,8 @@ import 'package:clide/src/files/ignore.dart';
 import 'package:clide/src/files/watcher.dart';
 import 'package:test/test.dart';
 
+import '../helpers/timeouts.dart';
+
 void main() {
   group('FileChangeKind', () {
     test('fromEvent maps every FileSystemEvent.type to a wire kind', () {
@@ -69,8 +71,8 @@ void main() {
       );
       await File('${sandbox.path}/new.txt').writeAsString('hi');
       final change = await saw.timeout(
-        const Duration(seconds: 5),
-        onTimeout: () => fail('no `new.txt` event within 5s'),
+        ioTimeout,
+        onTimeout: () => fail('no `new.txt` event within ${ioTimeout.inSeconds}s'),
       );
       expect(change.path, 'new.txt');
     });
@@ -115,13 +117,13 @@ void main() {
 
 /// Wait until [received] satisfies [predicate]. Polls the list (it
 /// gets mutated by the listener subscription) every 25 ms with a
-/// generous 8 s ceiling; fails loudly on miss instead of silently
-/// continuing as the old fixed-sleep tests did.
+/// generous [ioTimeout] ceiling; fails loudly on miss instead of
+/// silently continuing as the old fixed-sleep tests did.
 Future<void> _expectReceived<T>(List<T> received, bool Function(T) predicate) async {
-  final deadline = DateTime.now().add(const Duration(seconds: 8));
+  final deadline = DateTime.now().add(ioTimeout);
   while (!received.any(predicate)) {
     if (DateTime.now().isAfter(deadline)) {
-      fail('expected event never arrived within 8s; received=${received.length} entries');
+      fail('expected event never arrived within ${ioTimeout.inSeconds}s; received=${received.length} entries');
     }
     await Future<void>.delayed(const Duration(milliseconds: 25));
   }

test/helpers/timeouts.dart

@@ -0,0 +1,10 @@
+/// Shared test timeouts. Flutter-free on purpose, so both `dart test`
+/// (the pty / ipc suites) and `flutter test` files can import it.
+library;
+
+/// Generous timeout for waiting on real external I/O — PTY output, fs
+/// watcher events, socket round-trips. A working path responds in well
+/// under a second; this is pure headroom so transient scheduling latency
+/// doesn't flake the gate. A genuinely broken path still fails — just
+/// later. Tune here, once, rather than scattering magic seconds.
+const Duration ioTimeout = Duration(seconds: 20);

test/panes/registry_test.dart

@@ -13,6 +13,8 @@ import 'package:clide/clide.dart';
 import 'package:clide/src/panes/registry.dart';
 import 'package:test/test.dart';
 
+import '../helpers/timeouts.dart';
+
 void main() {
   if (!Platform.isLinux && !Platform.isMacOS) return;
 
@@ -63,8 +65,8 @@ void main() {
       );
 
       final decoded = await got.future.timeout(
-        const Duration(seconds: 5),
-        onTimeout: () => fail('pane.output never carried "hello-panes" within 5s'),
+        ioTimeout,
+        onTimeout: () => fail('pane.output never carried "hello-panes" within ${ioTimeout.inSeconds}s'),
       );
       expect(decoded, contains('hello-panes'));
       expect(sink.ofKind('pane.output'), isNotEmpty);

test/pty/session_test.dart

@@ -20,6 +20,8 @@ import 'package:clide/src/pty/errors.dart';
 import 'package:clide/src/pty/native_pty.dart';
 import 'package:test/test.dart';
 
+import '../helpers/timeouts.dart';
+
 void main() {
   if (!Platform.isLinux && !Platform.isMacOS) return;
 
@@ -38,7 +40,7 @@ void main() {
       );
       addTearDown(s.close);
 
-      final got = await _readUntil(s, 'hello-pty', const Duration(seconds: 20));
+      final got = await _readUntil(s, 'hello-pty', ioTimeout);
       expect(got, contains('hello-pty'));
     });
 
@@ -67,13 +69,13 @@ void main() {
       addTearDown(sub.cancel);
 
       await firstByte.future.timeout(
-        const Duration(seconds: 20),
-        onTimeout: () => fail('shell never produced its first byte within 20s'),
+        ioTimeout,
+        onTimeout: () => fail('shell never produced its first byte within ${ioTimeout.inSeconds}s'),
       );
 
       s.write(utf8.encode('echo write-test-ok\n'));
 
-      final result = await _waitForBuffer(buf, 'write-test-ok', const Duration(seconds: 20));
+      final result = await _waitForBuffer(buf, 'write-test-ok', ioTimeout);
       expect(result, contains('write-test-ok'));
     });
 
@@ -95,8 +97,8 @@ void main() {
 
       await s.close();
       await done.future.timeout(
-        const Duration(seconds: 10),
-        onTimeout: () => fail('output stream did not close within 10s after s.close()'),
+        ioTimeout,
+        onTimeout: () => fail('output stream did not close within ${ioTimeout.inSeconds}s after s.close()'),
       );
       expect(s.isClosed, isTrue);
     });
@@ -116,7 +118,7 @@ void main() {
       );
       addTearDown(s.close);
 
-      final got = await _readUntil(s, 'path-resolution-ok', const Duration(seconds: 20));
+      final got = await _readUntil(s, 'path-resolution-ok', ioTimeout);
       expect(got, contains('path-resolution-ok'));
     });