diff --git a/src/ClaudeDo.Worker/Config/WorkerConfig.cs b/src/ClaudeDo.Worker/Config/WorkerConfig.cs
index afcdff9..f060517 100644
--- a/src/ClaudeDo.Worker/Config/WorkerConfig.cs
+++ b/src/ClaudeDo.Worker/Config/WorkerConfig.cs
@@ -41,6 +41,10 @@ public sealed class WorkerConfig
     [JsonPropertyName("external_mcp_api_key")]
     public string? ExternalMcpApiKey { get; set; }
 
+    /// <summary>Interactive/streaming sessions idle longer than this are stopped by IdleSessionReaper. 0 disables reaping.</summary>
+    [JsonPropertyName("interactive_idle_timeout_minutes")]
+    public int InteractiveIdleTimeoutMinutes { get; set; } = 30;
+
     [JsonPropertyName("online_inbox")]
     public OnlineInboxConfig OnlineInbox { get; set; } = new();
 
diff --git a/src/ClaudeDo.Worker/Planning/InteractiveSessionService.cs b/src/ClaudeDo.Worker/Planning/InteractiveSessionService.cs
index 099790a..2a8cb21 100644
--- a/src/ClaudeDo.Worker/Planning/InteractiveSessionService.cs
+++ b/src/ClaudeDo.Worker/Planning/InteractiveSessionService.cs
@@ -70,7 +70,11 @@ public sealed class InteractiveSessionService
             "--permission-mode", "auto",
         };
 
-        Func<string, Task> onLine = line => _broadcaster.TaskMessage(taskId, "[stdout] " + line);
+        Func<string, Task> onLine = line =>
+        {
+            _registry.Touch(taskId);
+            return _broadcaster.TaskMessage(taskId, "[stdout] " + line);
+        };
 
         ILiveSession session;
         Task exitTask;
@@ -124,19 +128,26 @@ public sealed class InteractiveSessionService
     {
         if (!_registry.TryGet(taskId, out var session))
             throw new InvalidOperationException("No interactive session is running for this task.");
+        _registry.Touch(taskId);
         await session.SendUserMessageAsync(text, ct);
     }
 
     public async Task RemoveQueuedAsync(string taskId, string text, CancellationToken ct)
     {
         if (_registry.TryGet(taskId, out var session))
+        {
+            _registry.Touch(taskId);
             await session.RemoveQueuedAsync(text, ct);
+        }
     }
 
     public async Task InterruptAsync(string taskId, CancellationToken ct)
     {
         if (_registry.TryGet(taskId, out var session))
+        {
+            _registry.Touch(taskId);
             await session.InterruptAsync(ct);
+        }
     }
 
     public async Task StopAsync(string taskId, CancellationToken ct)
diff --git a/src/ClaudeDo.Worker/Program.cs b/src/ClaudeDo.Worker/Program.cs
index 29f4c48..7716b7a 100644
--- a/src/ClaudeDo.Worker/Program.cs
+++ b/src/ClaudeDo.Worker/Program.cs
@@ -82,6 +82,7 @@ builder.Services.AddSingleton<PlanningMergeOrchestrator>();
 builder.Services.AddSingleton<PlanningChainCoordinator>();
 builder.Services.AddSingleton<LiveSessionRegistry>();
 builder.Services.AddSingleton<InteractiveSessionService>();
+builder.Services.AddHostedService<IdleSessionReaper>();
 
 // Queue dispatch primitives. QueueWaker holds the wake semaphore; the queue picker
 // performs atomic Queued→Running claim. Both injected into the state service so it
diff --git a/src/ClaudeDo.Worker/Runner/IdleSessionReaper.cs b/src/ClaudeDo.Worker/Runner/IdleSessionReaper.cs
new file mode 100644
index 0000000..9d4a0c1
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/IdleSessionReaper.cs
@@ -0,0 +1,49 @@
+using ClaudeDo.Worker.Config;
+
+namespace ClaudeDo.Worker.Runner;
+
+// Stops interactive/streaming sessions that have gone idle. Interactive `claude` processes wait
+// on stdin and never exit on their own, and there is no client-disconnect teardown — so an
+// abandoned chat (UI closed, navigated away, crashed) keeps its claude.exe (+ conhost) alive for
+// the worker's entire lifetime. Under a long-running autostart worker these pile up (observed:
+// ~170 child processes). This sweep reaps the idle ones.
+public sealed class IdleSessionReaper : BackgroundService
+{
+    private static readonly TimeSpan SweepInterval = TimeSpan.FromMinutes(5);
+
+    private readonly LiveSessionRegistry _registry;
+    private readonly WorkerConfig _cfg;
+    private readonly ILogger<IdleSessionReaper> _logger;
+
+    public IdleSessionReaper(LiveSessionRegistry registry, WorkerConfig cfg, ILogger<IdleSessionReaper> logger)
+    {
+        _registry = registry;
+        _cfg = cfg;
+        _logger = logger;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var idleTimeout = TimeSpan.FromMinutes(_cfg.InteractiveIdleTimeoutMinutes);
+        if (idleTimeout <= TimeSpan.Zero)
+            return; // reaper disabled
+
+        using var timer = new PeriodicTimer(SweepInterval);
+        while (await timer.WaitForNextTickAsync(stoppingToken))
+        {
+            try
+            {
+                var reaped = await _registry.ReapIdleAsync(DateTime.UtcNow, idleTimeout);
+                if (reaped.Count > 0)
+                    _logger.LogInformation(
+                        "Reaped {session_count} idle interactive session(s) after {idle_minutes} min: {task_ids}",
+                        reaped.Count, _cfg.InteractiveIdleTimeoutMinutes, string.Join(", ", reaped));
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Idle session reap sweep failed");
+            }
+        }
+    }
+}
diff --git a/src/ClaudeDo.Worker/Runner/LiveSessionRegistry.cs b/src/ClaudeDo.Worker/Runner/LiveSessionRegistry.cs
index 60d4376..90a0c64 100644
--- a/src/ClaudeDo.Worker/Runner/LiveSessionRegistry.cs
+++ b/src/ClaudeDo.Worker/Runner/LiveSessionRegistry.cs
@@ -5,28 +5,47 @@ namespace ClaudeDo.Worker.Runner;
 
 // Singleton in-memory registry of active live streaming sessions.
 // A session's lifetime matches its associated task run; dead entries are removed by the runner.
+//
+// Interactive (stream-json) sessions never exit on their own — they wait on stdin — and there is
+// no client-disconnect teardown, so an abandoned chat would otherwise keep its claude.exe alive
+// for the worker's whole lifetime. IdleSessionReaper periodically stops sessions that have seen
+// no activity past a timeout (see ReapIdleAsync); Touch() records that activity.
 public sealed class LiveSessionRegistry
 {
-    private readonly ConcurrentDictionary<string, ILiveSession> _sessions = new();
+    private sealed class Entry
+    {
+        public required ILiveSession Session { get; init; }
+        public long LastActivityTicksUtc;
+    }
+
+    private readonly ConcurrentDictionary<string, Entry> _sessions = new();
 
     public void Register(string taskId, ILiveSession session)
     {
         if (_sessions.TryRemove(taskId, out var existing))
         {
             // Best-effort stop of the replaced session; don't await to avoid deadlock risk.
-            _ = existing.StopAsync().ContinueWith(t =>
+            _ = existing.Session.StopAsync().ContinueWith(t =>
             {
                 if (t.IsFaulted) { /* swallow — old session is already orphaned */ }
             }, TaskScheduler.Default);
         }
-        _sessions[taskId] = session;
+        _sessions[taskId] = new Entry { Session = session, LastActivityTicksUtc = DateTime.UtcNow.Ticks };
+    }
+
+    // Marks a session as active so the idle reaper leaves it alone. Called on every user
+    // message and every output line. No-op if the session is not (yet) registered.
+    public void Touch(string taskId)
+    {
+        if (_sessions.TryGetValue(taskId, out var entry))
+            Interlocked.Exchange(ref entry.LastActivityTicksUtc, DateTime.UtcNow.Ticks);
     }
 
     public bool TryGet(string taskId, out ILiveSession session)
     {
-        if (_sessions.TryGetValue(taskId, out var s))
+        if (_sessions.TryGetValue(taskId, out var entry))
         {
-            session = s;
+            session = entry.Session;
             return true;
         }
         session = null!;
@@ -37,7 +56,32 @@ public sealed class LiveSessionRegistry
 
     public async Task StopAsync(string taskId)
     {
-        if (_sessions.TryRemove(taskId, out var session))
-            await session.StopAsync();
+        if (_sessions.TryRemove(taskId, out var entry))
+            await entry.Session.StopAsync();
+    }
+
+    // Stops and removes every session whose last activity is older than (nowUtc - idleTimeout),
+    // skipping any session with a turn in flight (an agent that's actively working, even if quiet).
+    // Returns the reaped task ids.
+    public async Task<IReadOnlyList<string>> ReapIdleAsync(DateTime nowUtc, TimeSpan idleTimeout)
+    {
+        var cutoffTicks = (nowUtc - idleTimeout).Ticks;
+        List<string>? reaped = null;
+
+        foreach (var kvp in _sessions)
+        {
+            var entry = kvp.Value;
+            if (entry.Session.IsTurnInFlight) continue;
+            if (Interlocked.Read(ref entry.LastActivityTicksUtc) > cutoffTicks) continue;
+
+            if (_sessions.TryRemove(kvp.Key, out var removed))
+            {
+                try { await removed.Session.StopAsync(); }
+                catch { /* already dead — leave it removed */ }
+                (reaped ??= new()).Add(kvp.Key);
+            }
+        }
+
+        return reaped ?? (IReadOnlyList<string>)Array.Empty<string>();
     }
 }
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/LiveSessionRegistryTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/LiveSessionRegistryTests.cs
index 54ab2c8..89b48b3 100644
--- a/tests/ClaudeDo.Worker.Tests/Runner/LiveSessionRegistryTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Runner/LiveSessionRegistryTests.cs
@@ -8,7 +8,7 @@ public sealed class LiveSessionRegistryTests
     private sealed class FakeLiveSession : ILiveSession
     {
         public bool StopCalled { get; private set; }
-        public bool IsTurnInFlight => false;
+        public bool IsTurnInFlight { get; set; }
 
         public Task SendUserMessageAsync(string text, CancellationToken ct) => Task.CompletedTask;
         public Task RemoveQueuedAsync(string text, CancellationToken ct) => Task.CompletedTask;
@@ -90,4 +90,56 @@ public sealed class LiveSessionRegistryTests
         var registry = new LiveSessionRegistry();
         await registry.StopAsync("no-such-task"); // should not throw
     }
+
+    [Fact]
+    public async Task ReapIdleAsync_StopsAndRemovesIdleSession()
+    {
+        var registry = new LiveSessionRegistry();
+        var session = new FakeLiveSession();
+        registry.Register("task-1", session);
+
+        // Sweep "now" is an hour past registration, well beyond the 30-min idle window.
+        var reaped = await registry.ReapIdleAsync(DateTime.UtcNow.AddMinutes(60), TimeSpan.FromMinutes(30));
+
+        Assert.Contains("task-1", reaped);
+        Assert.True(session.StopCalled);
+        Assert.False(registry.TryGet("task-1", out _));
+    }
+
+    [Fact]
+    public async Task ReapIdleAsync_KeepsRecentlyActiveSession()
+    {
+        var registry = new LiveSessionRegistry();
+        var session = new FakeLiveSession();
+        registry.Register("task-1", session);
+
+        var reaped = await registry.ReapIdleAsync(DateTime.UtcNow, TimeSpan.FromMinutes(30));
+
+        Assert.Empty(reaped);
+        Assert.False(session.StopCalled);
+        Assert.True(registry.TryGet("task-1", out _));
+    }
+
+    [Fact]
+    public async Task ReapIdleAsync_SkipsSessionWithTurnInFlight()
+    {
+        var registry = new LiveSessionRegistry();
+        var session = new FakeLiveSession { IsTurnInFlight = true };
+        registry.Register("task-1", session);
+
+        // Idle long enough to reap, but a turn is in flight → must be left alone.
+        var reaped = await registry.ReapIdleAsync(DateTime.UtcNow.AddMinutes(60), TimeSpan.FromMinutes(30));
+
+        Assert.Empty(reaped);
+        Assert.False(session.StopCalled);
+        Assert.True(registry.TryGet("task-1", out _));
+    }
+
+    [Fact]
+    public async Task ReapIdleAsync_NoSessions_ReturnsEmpty()
+    {
+        var registry = new LiveSessionRegistry();
+        var reaped = await registry.ReapIdleAsync(DateTime.UtcNow, TimeSpan.FromMinutes(30));
+        Assert.Empty(reaped);
+    }
 }