Add READY state for human-in-the-loop verification

Top-level tasks now land in READY after successful execution instead of
going directly to COMPLETED. Subtasks (with parent_task_id) skip the gate
and remain COMPLETED. Users accept or reject via new API endpoints:

  POST /api/tasks/{id}/accept  → READY → COMPLETED
  POST /api/tasks/{id}/reject  → READY → PENDING (with rejection_comment)

- task: add StateReady, RejectionComment field, update ValidTransition
- storage: migrate rejection_comment column, add RejectTask method
- executor: route top-level vs subtask to READY vs COMPLETED
- api: /accept and /reject handlers with 409 on invalid state

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2 files changed, 40 insertions, 8 deletions

diff --git a/internal/executor/executor.go b/internal/executor/executor.go
index 68ebdf3..d25d3b4 100644
--- a/internal/executor/executor.go
+++ b/internal/executor/executor.go
@@ -149,8 +149,13 @@ func (p *Pool) execute(ctx context.Context, t *task.Task) {
 			p.store.UpdateTaskState(t.ID, task.StateFailed)
 		}
 	} else {
-		exec.Status = "COMPLETED"
-		p.store.UpdateTaskState(t.ID, task.StateCompleted)
+		if t.ParentTaskID == "" {
+			exec.Status = "READY"
+			p.store.UpdateTaskState(t.ID, task.StateReady)
+		} else {
+			exec.Status = "COMPLETED"
+			p.store.UpdateTaskState(t.ID, task.StateCompleted)
+		}
 	}
 
 	if updateErr := p.store.UpdateExecution(exec); updateErr != nil {
diff --git a/internal/executor/executor_test.go b/internal/executor/executor_test.go
index 5d6a55a..18a79bb 100644
--- a/internal/executor/executor_test.go
+++ b/internal/executor/executor_test.go
@@ -73,13 +73,41 @@ func makeTask(id string) *task.Task {
 	}
 }
 
-func TestPool_Submit_Success(t *testing.T) {
+func TestPool_Submit_TopLevel_GoesToReady(t *testing.T) {
 	store := testStore(t)
 	runner := &mockRunner{}
 	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
 	pool := NewPool(2, runner, store, logger)
 
-	tk := makeTask("ps-1")
+	tk := makeTask("ps-1") // no ParentTaskID → top-level
+	store.CreateTask(tk)
+
+	if err := pool.Submit(context.Background(), tk); err != nil {
+		t.Fatalf("submit: %v", err)
+	}
+
+	result := <-pool.Results()
+	if result.Err != nil {
+		t.Errorf("expected no error, got: %v", result.Err)
+	}
+	if result.Execution.Status != "READY" {
+		t.Errorf("status: want READY, got %q", result.Execution.Status)
+	}
+
+	got, _ := store.GetTask("ps-1")
+	if got.State != task.StateReady {
+		t.Errorf("task state: want READY, got %v", got.State)
+	}
+}
+
+func TestPool_Submit_Subtask_GoesToCompleted(t *testing.T) {
+	store := testStore(t)
+	runner := &mockRunner{}
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
+	pool := NewPool(2, runner, store, logger)
+
+	tk := makeTask("sub-1")
+	tk.ParentTaskID = "parent-99" // subtask
 	store.CreateTask(tk)
 
 	if err := pool.Submit(context.Background(), tk); err != nil {
@@ -94,8 +122,7 @@ func TestPool_Submit_Success(t *testing.T) {
 		t.Errorf("status: want COMPLETED, got %q", result.Execution.Status)
 	}
 
-	// Verify task state in DB.
-	got, _ := store.GetTask("ps-1")
+	got, _ := store.GetTask("sub-1")
 	if got.State != task.StateCompleted {
 		t.Errorf("task state: want COMPLETED, got %v", got.State)
 	}
@@ -195,8 +222,8 @@ func TestPool_ConcurrentExecution(t *testing.T) {
 
 	for i := 0; i < 3; i++ {
 		result := <-pool.Results()
-		if result.Execution.Status != "COMPLETED" {
-			t.Errorf("task %s: want COMPLETED, got %q", result.TaskID, result.Execution.Status)
+		if result.Execution.Status != "READY" {
+			t.Errorf("task %s: want READY, got %q", result.TaskID, result.Execution.Status)
 		}
 	}