fix(worker): make list_tasks/batch_get_tasks lean by default

list_tasks on a list of ~100 verbosely-described tasks could return
390k+ characters in one call, blowing past the caller's token limit.
Both tools now default to lean TaskRefDto references (no
Description/Result) and take an includeDescription flag to opt back
into the full TaskDto payload — same flag-alongside-nullable-payload
idiom already used by BatchGetTaskResult/TaskConfigResult. get_task is
unchanged.

tests/ClaudeDo.Worker.Tests/External/ExternalMcpServiceTests.cs

@@ -947,10 +947,11 @@ public sealed class ExternalMcpServiceTests : IDisposable
         await SeedTaskAsync(listId, "idle", TaskStatus.Idle);
         var sut = NewService();
 
-        var result = await sut.ListTasks(listId, null, "WaitingForReview", CancellationToken.None);
+        var result = await sut.ListTasks(listId, null, "WaitingForReview", cancellationToken: CancellationToken.None);
 
-        Assert.Single(result);
-        Assert.Equal("WaitingForReview", result[0].Status);
+        Assert.NotNull(result.Tasks);
+        Assert.Single(result.Tasks!);
+        Assert.Equal("WaitingForReview", result.Tasks![0].Status);
     }
 
     [Fact]
@@ -961,10 +962,47 @@ public sealed class ExternalMcpServiceTests : IDisposable
         await SeedTaskAsync(listId, "done", TaskStatus.Done);
         var sut = NewService();
 
-        var result = await sut.ListTasks(listId, null, "WaitingForChildren", CancellationToken.None);
+        var result = await sut.ListTasks(listId, null, "WaitingForChildren", cancellationToken: CancellationToken.None);
 
-        Assert.Single(result);
-        Assert.Equal("WaitingForChildren", result[0].Status);
+        Assert.NotNull(result.Tasks);
+        Assert.Single(result.Tasks!);
+        Assert.Equal("WaitingForChildren", result.Tasks![0].Status);
+    }
+
+    [Fact]
+    public async Task ListTasks_Default_ReturnsLeanReferences_NoDescriptionOrTasksFull()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId, "with desc");
+        task.Description = "a long description that should not come back by default";
+        await _tasks.UpdateAsync(task);
+        var sut = NewService();
+
+        var result = await sut.ListTasks(listId, cancellationToken: CancellationToken.None);
+
+        Assert.False(result.IncludeDescription);
+        Assert.NotNull(result.Tasks);
+        Assert.Null(result.TasksFull);
+        Assert.Single(result.Tasks!);
+        Assert.Equal(task.Id, result.Tasks![0].Id);
+    }
+
+    [Fact]
+    public async Task ListTasks_IncludeDescriptionTrue_ReturnsFullTasks()
+    {
+        var listId = await SeedListAsync();
+        var task = await SeedTaskAsync(listId, "with desc");
+        task.Description = "the full description";
+        await _tasks.UpdateAsync(task);
+        var sut = NewService();
+
+        var result = await sut.ListTasks(listId, includeDescription: true, cancellationToken: CancellationToken.None);
+
+        Assert.True(result.IncludeDescription);
+        Assert.Null(result.Tasks);
+        Assert.NotNull(result.TasksFull);
+        Assert.Single(result.TasksFull!);
+        Assert.Equal("the full description", result.TasksFull![0].Description);
     }
 
     // ── MergeTask allowWaitingForReview ───────────────────────────────────────