Fix terminal session resume reconnect

apps/mobile_app/lib/features/terminal/terminal_page.dart

@@ -31,7 +31,8 @@ class TerminalPage extends ConsumerStatefulWidget {
   ConsumerState<TerminalPage> createState() => _TerminalPageState();
 }
 
-class _TerminalPageState extends ConsumerState<TerminalPage> {
+class _TerminalPageState extends ConsumerState<TerminalPage>
+    with WidgetsBindingObserver {
   static const List<_QuickTerminalKey> _quickTerminalKeys = [
     _QuickTerminalKey(keyId: 'esc', label: 'Esc', input: '\u001b'),
     _QuickTerminalKey(keyId: 'tab', label: 'Tab', input: '\t'),
@@ -57,6 +58,7 @@ class _TerminalPageState extends ConsumerState<TerminalPage> {
   @override
   void initState() {
     super.initState();
+    WidgetsBinding.instance.addObserver(this);
     _coordinator = TerminalSessionCoordinator(
       controller: controller,
       apiClient: ref.read(agentApiClientProvider),
@@ -92,6 +94,7 @@ class _TerminalPageState extends ConsumerState<TerminalPage> {
 
   @override
   void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
     _terminalFocusNode.dispose();
     _inputController.dispose();
     _terminalScrollController.dispose();
@@ -100,6 +103,16 @@ class _TerminalPageState extends ConsumerState<TerminalPage> {
     super.dispose();
   }
 
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state != AppLifecycleState.resumed) {
+      return;
+    }
+
+    _diagnosticLog.add('app.lifecycle.resumed', widget.session.sessionId);
+    unawaited(_coordinator.reconnectNow());
+  }
+
   Future<void> _openSiblingTerminal() async {
     final project = widget.project;
     if (project == null) {

apps/mobile_app/test/widget_test.dart

@@ -527,6 +527,41 @@ void main() {
     expect(find.text('codex-main'), findsOneWidget);
   });
 
+  testWidgets('terminal page reconnects when the app resumes', (tester) async {
+    final transportFactory = _QueuedTerminalSocketTransportFactory();
+
+    await _pumpApp(
+      tester,
+      projectRepository: _FakeProjectRepository(),
+      sessionRepository: _FakeSessionRepository(),
+      socketFactory: TerminalSocketSessionFactory(
+        transportFactory: transportFactory.create,
+      ),
+    );
+
+    await _openProjectTerminal(tester);
+
+    expect(transportFactory.createCount, 1);
+
+    tester.binding.handleAppLifecycleStateChanged(AppLifecycleState.inactive);
+    await tester.pump();
+    tester.binding.handleAppLifecycleStateChanged(AppLifecycleState.hidden);
+    await tester.pump();
+    tester.binding.handleAppLifecycleStateChanged(AppLifecycleState.paused);
+    await tester.pump();
+    tester.binding.handleAppLifecycleStateChanged(AppLifecycleState.hidden);
+    await tester.pump();
+    tester.binding.handleAppLifecycleStateChanged(AppLifecycleState.inactive);
+    await tester.pump();
+    tester.binding.handleAppLifecycleStateChanged(AppLifecycleState.resumed);
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 2));
+    await tester.pumpAndSettle();
+
+    expect(transportFactory.createCount, 2);
+    expect(find.text('codex-main'), findsOneWidget);
+  });
+
   testWidgets('terminal page can open another terminal for the same project', (
     tester,
   ) async {

apps/windows_agent/src/TermRemoteCtl.Agent/Terminal/ConPtyProcessSession.cs

@@ -62,6 +62,15 @@ internal sealed class ConPtyProcessSession : IConPtySession
         await Task.CompletedTask.ConfigureAwait(false);
     }
 
+    public ValueTask<bool> IsAliveAsync(CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+        var isAlive = !_disposed &&
+            !_shutdown.IsCancellationRequested &&
+            TryGetExitCode() is null;
+        return ValueTask.FromResult(isAlive);
+    }
+
     public async Task WriteInputAsync(string input, CancellationToken cancellationToken)
     {
         ThrowIfDisposed();

apps/windows_agent/src/TermRemoteCtl.Agent/Terminal/HelperBackedConPtySession.cs

@@ -108,6 +108,17 @@ internal sealed class HelperBackedConPtySession : IConPtySession
         _started = true;
     }
 
+    public ValueTask<bool> IsAliveAsync(CancellationToken cancellationToken)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+        var isAlive = !_disposed &&
+            _started &&
+            _helperProcess is { HasExited: false } &&
+            _commandPipe is { IsConnected: true } &&
+            _outputPipe is { IsConnected: true };
+        return ValueTask.FromResult(isAlive);
+    }
+
     public async Task WriteInputAsync(string input, CancellationToken cancellationToken)
     {
         if (_commandWriter is null)

apps/windows_agent/src/TermRemoteCtl.Agent/Terminal/IConPtySession.cs

@@ -6,6 +6,8 @@ internal interface IConPtySession : IAsyncDisposable
 
     Task StartAsync(CancellationToken cancellationToken);
 
+    ValueTask<bool> IsAliveAsync(CancellationToken cancellationToken);
+
     Task WriteInputAsync(string input, CancellationToken cancellationToken);
 
     Task ResizeAsync(int columns, int rows, CancellationToken cancellationToken);

apps/windows_agent/src/TermRemoteCtl.Agent/Terminal/PowerShellSessionHost.cs

@@ -24,9 +24,18 @@ internal sealed class PowerShellSessionHost : ISessionHost, IAsyncDisposable
         ArgumentException.ThrowIfNullOrWhiteSpace(sessionId);
         ConPtyInterop.EnsureSupported();
 
-        if (_sessions.ContainsKey(sessionId))
+        if (_sessions.TryGetValue(sessionId, out var existingSession))
         {
-            return;
+            if (await existingSession.IsAliveAsync(cancellationToken).ConfigureAwait(false))
+            {
+                return;
+            }
+
+            if (_sessions.TryRemove(new KeyValuePair<string, IConPtySession>(sessionId, existingSession)))
+            {
+                existingSession.OutputReceived -= HandleSessionOutput;
+                await existingSession.DisposeAsync().ConfigureAwait(false);
+            }
         }
 
         if (!_sessionRegistry.TryGet(sessionId, out var record) || record is null)

apps/windows_agent/tests/TermRemoteCtl.Agent.Tests/Terminal/PowerShellSessionHostTests.cs

@@ -56,6 +56,25 @@ public class PowerShellSessionHostTests
         Assert.True(history.HasMoreAbove);
     }
 
+    [Fact]
+    public async Task StartAsync_Recreates_Unhealthy_Existing_Session()
+    {
+        var factory = new FakeConPtySessionFactory();
+        using var harness = HostHarness.Create(factory);
+        await using var host = harness.Host;
+        var session = harness.Registry.Create("alpha", DateTimeOffset.UtcNow);
+
+        await host.StartAsync(session.SessionId, CancellationToken.None);
+        var firstSession = factory.CreatedSessions.Single();
+        firstSession.IsAlive = false;
+
+        await host.StartAsync(session.SessionId, CancellationToken.None);
+
+        Assert.Equal(2, factory.CreatedSessions.Count);
+        Assert.True(firstSession.DisposeCount > 0);
+        Assert.True(factory.CreatedSessions.Last().StartCount > 0);
+    }
+
     private sealed class HostHarness : IDisposable
     {
         private HostHarness(string dataRoot, SessionRegistry registry, PowerShellSessionHost host)
@@ -98,20 +117,29 @@ public class PowerShellSessionHostTests
 
     private sealed class FakeConPtySessionFactory : IConPtySessionFactory
     {
-        public FakeConPtySession Session { get; } = new();
+        public List<FakeConPtySession> CreatedSessions { get; } = [];
         public string? LastWorkingDirectory { get; private set; }
 
+        public FakeConPtySession Session => CreatedSessions.Last();
+
         public IConPtySession Create(string sessionId, string? workingDirectory = null)
         {
-            Session.SessionId = sessionId;
+            var session = new FakeConPtySession
+            {
+                SessionId = sessionId,
+            };
+            CreatedSessions.Add(session);
             LastWorkingDirectory = workingDirectory;
-            return Session;
+            return session;
         }
     }
 
     private sealed class FakeConPtySession : IConPtySession
     {
         public string SessionId { get; set; } = string.Empty;
+        public bool IsAlive { get; set; } = true;
+        public int StartCount { get; private set; }
+        public int DisposeCount { get; private set; }
 
         public event EventHandler<TerminalOutputEventArgs>? OutputReceived;
 
@@ -119,9 +147,15 @@ public class PowerShellSessionHostTests
 
         public Task StartAsync(CancellationToken cancellationToken)
         {
+            StartCount += 1;
             return Task.CompletedTask;
         }
 
+        public ValueTask<bool> IsAliveAsync(CancellationToken cancellationToken)
+        {
+            return ValueTask.FromResult(IsAlive);
+        }
+
         public Task WriteInputAsync(string input, CancellationToken cancellationToken)
         {
             return Task.CompletedTask;
@@ -140,6 +174,7 @@ public class PowerShellSessionHostTests
 
         public ValueTask DisposeAsync()
         {
+            DisposeCount += 1;
             return ValueTask.CompletedTask;
         }
     }