Make task state store-owned and signal its changes to the lead

api/openapi.yaml

@@ -1012,7 +1012,7 @@ components:
 
     Task:
       type: object
-      required: [id, project_id, title, merge_title, branch, worktree_path, base_ref, port_base, color, status, created_by, created_at, reviewing, merging, discarding, merging_into_parent, summary_seq]
+      required: [id, project_id, title, merge_title, branch, worktree_path, base_ref, port_base, color, status, created_by, created_at, state, merging, discarding, merging_into_parent, summary_seq]
       properties:
         id: { type: string }
         project_id: { type: string }
@@ -1038,7 +1038,11 @@ components:
         workflow: { type: string, description: "The name of the workflow the task froze at creation (getTaskWorkflow has its copy); absent for a task without one." }
         workflow_run: { type: string, description: "With workflow: the id every task of one run of the workflow shares." }
         workflow_stage: { type: string, description: "With workflow: the name of the stage this task runs." }
-        reviewing: { type: boolean, description: "Whether a review of one of the task's snapshots is running." }
+        state:
+          type: string
+          description: "What the task is doing, kept by the store in the same transaction as every change to it (a task.state event carries each change): merged or discarded once closed, else discarding, merging, the state of its agent's latest live session when that isn't idle, reviewing while a review runs, review_pending between a turn's end and its snapshot's review starting or being skipped, idle, or no_agent."
+          enum: [running, idle, review_pending, reviewing, merging, discarding, merged, discarded, no_agent]
+          x-enum-varnames: [TaskStateRunning, TaskStateIdle, TaskStateReviewPending, TaskStateReviewing, TaskStateMerging, TaskStateDiscarding, TaskStateMerged, TaskStateDiscarded, TaskStateNoAgent]
         merging: { type: boolean, description: "Whether a Merge was started and its turn hasn't ended yet." }
         discarding: { type: boolean, description: "Whether a Discard was started and the task isn't closed yet: its summary turn is waiting for the running turn, running, or done and the task is being removed." }
         parent_task_id: { type: string, description: "The task whose agent created this one as its subtask; absent for other tasks." }