feat(attachments): inject reference files into the run + clean up files on delete

TaskRunner appends attached files (absolute paths) to the run prompt as the
read-only Reference files section. Task and list deletes now remove the
on-disk attachment dir eagerly, and a startup AttachmentOrphanRecovery sweep
drops any attachments/<taskId>/ whose task no longer exists (covers list
cascade and planning-discard paths).

tests/ClaudeDo.Worker.Tests/Lifecycle/AttachmentOrphanRecoveryTests.cs

@@ -0,0 +1,74 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Worker.Lifecycle;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace ClaudeDo.Worker.Tests.Lifecycle;
+
+public sealed class AttachmentOrphanRecoveryTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly string _attachRoot;
+
+    public AttachmentOrphanRecoveryTests()
+    {
+        _attachRoot = Path.Combine(Path.GetTempPath(), $"claudedo_orph_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_attachRoot);
+    }
+
+    public void Dispose()
+    {
+        _db.Dispose();
+        try { Directory.Delete(_attachRoot, recursive: true); } catch { }
+    }
+
+    [Fact]
+    public async Task StartAsync_DeletesOrphanDir_KeepsLiveTaskDir()
+    {
+        // Seed one real task.
+        string listId = Guid.NewGuid().ToString();
+        string liveTaskId = Guid.NewGuid().ToString();
+        using (var ctx = _db.CreateContext())
+        {
+            ctx.Lists.Add(new ListEntity { Id = listId, Name = "L", CreatedAt = DateTime.UtcNow });
+            ctx.Tasks.Add(new TaskEntity
+            {
+                Id = liveTaskId, ListId = listId, Title = "T",
+                Status = TaskStatus.Idle, CreatedAt = DateTime.UtcNow,
+            });
+            await ctx.SaveChangesAsync();
+        }
+
+        // Create two attachment directories: one for the live task, one orphan.
+        var store = new AttachmentStore(_attachRoot);
+        var liveDir = store.TaskDir(liveTaskId);
+        var orphanId = Guid.NewGuid().ToString();
+        var orphanDir = store.TaskDir(orphanId);
+        Directory.CreateDirectory(liveDir);
+        Directory.CreateDirectory(orphanDir);
+
+        var sut = new AttachmentOrphanRecovery(
+            _db.CreateFactory(), store,
+            NullLogger<AttachmentOrphanRecovery>.Instance);
+
+        await sut.StartAsync(CancellationToken.None);
+
+        Assert.True(Directory.Exists(liveDir), "Live task dir should be kept");
+        Assert.False(Directory.Exists(orphanDir), "Orphan dir should be deleted");
+    }
+
+    [Fact]
+    public async Task StartAsync_NoAttachmentRoot_IsNoop()
+    {
+        // Use a root that does not exist — should complete without throwing.
+        var missingRoot = Path.Combine(Path.GetTempPath(), $"claudedo_missing_{Guid.NewGuid():N}");
+        var store = new AttachmentStore(missingRoot);
+
+        var sut = new AttachmentOrphanRecovery(
+            _db.CreateFactory(), store,
+            NullLogger<AttachmentOrphanRecovery>.Instance);
+
+        await sut.StartAsync(CancellationToken.None); // must not throw
+    }
+}