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.

src/ClaudeDo.Worker/External/ExternalMcpService.cs

@@ -47,6 +47,15 @@ public sealed record TaskRefDto(
     int SortOrder,
     bool IsMyDay);
 
+// tasks is populated when includeDescription=false (the default): lean references, no
+// Description/Result. tasksFull is populated when includeDescription=true: full tasks incl.
+// Description/Result. Exactly one of the two is non-null per the includeDescription flag —
+// same "flag alongside nullable payload" idiom as BatchGetTaskResult.
+public sealed record ListTasksResult(
+    bool IncludeDescription,
+    IReadOnlyList<TaskRefDto>? Tasks,
+    IReadOnlyList<TaskDto>? TasksFull);
+
 public sealed record WorktreeInfoDto(
     string Path, string Branch, string HeadCommit, string BaseCommit,
     int Ahead, int Behind, bool IsDirty, string? MergeCommit = null);
@@ -139,11 +148,17 @@ public sealed class ExternalMcpService
 
     [McpServerTool, Description(
         "List tasks in a given list. Optionally filter by creator (createdBy) and/or status. " +
-        "Valid status values: Idle, Queued, Running, WaitingForReview, WaitingForChildren, Done, Failed, Cancelled.")]
-    public async Task<IReadOnlyList<TaskDto>> ListTasks(
+        "Valid status values: Idle, Queued, Running, WaitingForReview, WaitingForChildren, Done, Failed, Cancelled. " +
+        "includeDescription=false (default): returns lean task references in `tasks` (no Description/Result) — " +
+        "use this unless you actually need the description text, since a list of verbosely-described tasks can " +
+        "otherwise blow past the response size limit. " +
+        "includeDescription=true: returns full tasks (incl. Description/Result) in `tasksFull` instead; `tasks` is " +
+        "null in that case.")]
+    public async Task<ListTasksResult> ListTasks(
         string listId,
         string? createdBy = null,
         string? status = null,
+        bool includeDescription = false,
         CancellationToken cancellationToken = default)
     {
         TaskStatus? statusFilter = null;
@@ -162,7 +177,10 @@ public sealed class ExternalMcpService
         if (statusFilter is not null)
             query = query.Where(t => t.Status == statusFilter);
 
-        return query.Select(ToDto).ToList();
+        var filtered = query.ToList();
+        return includeDescription
+            ? new ListTasksResult(true, null, filtered.Select(ToDto).ToList())
+            : new ListTasksResult(false, filtered.Select(ToRefDto).ToList(), null);
     }
 
     [McpServerTool, Description(
@@ -177,6 +195,15 @@ public sealed class ExternalMcpService
         return ToDto(task);
     }
 
+    // Lean counterpart to GetTask, used internally by BatchGetTasks' default (includeDescription=false)
+    // path. Not an MCP tool itself — GetTask's own behavior stays untouched.
+    internal async Task<TaskRefDto> GetTaskRefAsync(string taskId, CancellationToken cancellationToken)
+    {
+        var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
+            ?? throw new InvalidOperationException($"Task {taskId} not found.");
+        return ToRefDto(task);
+    }
+
     [McpServerTool, Description(
         "Create a new task in the given list. Set queueImmediately=true to enqueue it for agent execution. " +
         "Set model to the cheapest model that can do the task well — 'haiku' for trivial/mechanical work, " +