docs: describe the list-scoped five-phase handler

src/ClaudeDo.Worker/CLAUDE.md

@@ -33,7 +33,7 @@ Interfaces (e.g. `IQueueWaker`, `IPrimeClock`, `ITaskStateService`) live in an `
 - **OverrideSlotService** — owns `RunNow` / `ContinueTask`; goes through `TaskStateService.StartRunningAsync` (caller-driven, serialized by slot lock).
 - **StaleTaskRecovery** — startup-only service; calls `TaskStateService.RecoverStaleRunningAsync` to flip orphaned `Running` rows to `Failed`.
 - **External/*** — always-on MCP tools for general Claude sessions, scoped to *starting* and *observing* sessions (no worktree/merge, multi-turn, planning, or app-settings writes). Auth via optional `X-ClaudeDo-Key` header. Registered explicitly in `Program.cs`'s external app via `.WithTools<T>()`. Every optional/filter parameter across these tools must carry a C# default value (e.g. `string? status = null`) — the MCP schema only marks a parameter optional when it has one; nullability alone doesn't do it (`ExternalMcpToolSchemaTests` guards this by reflection). `ExternalMcpExceptionFilter.Wrap` is registered as a call-tool filter so `InvalidOperationException`/`ArgumentException` messages survive as `McpException` — otherwise the SDK's own catch-all replaces any non-`McpException` with a generic "An error occurred invoking 'X'." Organized by concern:
-  - `ExternalMcpService` — task CRUD + execution: `ListTaskLists`, `ListTasks`, `GetTask`, `AddTask`, `AddSubtask`, `UpdateTask`, `UpdateTaskStatus` (`Idle` / `Queued`), `GetTaskStatusValues`, `ReviewTask` (`approve` / `reject_rerun` / `reject_park` / `cancel` for a WaitingForReview task; approve is review+merge exactly like the hub's `ApproveReview` — unit merge for parents, worktree merge into optional `targetBranch` for childless tasks, conflicts reported in the `ReviewTaskResult`), `RunTaskNow`, `ContinueTask`, `CancelTask`, `DeleteTask`; worktree/git: `GetTaskWorktree`, `GetTaskDiff`, `MergeTask`, `ListWorktrees`, `CleanupTaskWorktree`
+  - `ExternalMcpService` — task CRUD + execution: `ListTaskLists`, `ListTasks`, `GetTask`, `AddTask`, `AddSubtask`, `UpdateTask`, `UpdateTaskStatus` (`Idle` / `Queued` / `Cancelled` — `Cancelled` goes through `TaskStateService.CancelAsync(..., allowFromIdle: true)`, the only caller that opts into cancelling from `Idle`; `PlanningChainCoordinator` relies on `Idle` staying a no-op there by default, since a child parked back to `Idle` mid-chain is a manual opt-out signal), `GetTaskStatusValues`, `ReviewTask` (`approve` / `reject_rerun` / `reject_park` / `cancel` for a WaitingForReview task; approve is review+merge exactly like the hub's `ApproveReview` — unit merge for parents, worktree merge into optional `targetBranch` for childless tasks, conflicts reported in the `ReviewTaskResult`), `RunTaskNow`, `ContinueTask`, `CancelTask`, `DeleteTask`; worktree/git: `GetTaskWorktree`, `GetTaskDiff`, `MergeTask`, `ListWorktrees`, `CleanupTaskWorktree`
   - `BatchMcpTools` — best-effort batch variants that loop the `ExternalMcpService` single-entity methods (sequential — the scoped DbContext is not thread-safe; merge/review stay single-task): `BatchGetTasks`, `BatchAddTasks`, `BatchUpdateTaskStatus`, `BatchCancelTasks`, `BatchDeleteTasks`, `BatchSetMyDay`, `BatchCleanupTaskWorktrees`. Every tool returns a per-item result array ({ id/index, ok, error?, … }) — a failing item never aborts the rest — and rejects batches over 100 items.
   - `ListMcpTools` — `CreateList`, `UpdateList`, `DeleteList`
   - `ConfigMcpTools` — `GetListConfig`, `SetListConfig`, `GetTaskConfig`, `SetTaskConfig`
@@ -72,7 +72,7 @@ Interfaces (e.g. `IQueueWaker`, `IPrimeClock`, `ITaskStateService`) live in an `
 Allowed transitions (enforced by `TaskStateService`):
 
 ```
-Idle               → Queued | Running (RunNow)
+Idle               → Queued | Running (RunNow) | Cancelled (external update_task_status only, allowFromIdle: true)
 Queued             → Running | Cancelled | Idle | Failed (OverrideSlotService preflight gap: RunAsync can fail before StartRunningAsync is called)
 Running            → WaitingForReview (standalone success, no children)
                    | WaitingForChildren (parent with pending children)