executor: BLOCKED→READY for top-level tasks with subtasks

When a top-level task (ParentTaskID == "") finishes successfully,
check for subtasks before deciding the next state:
- subtasks exist → BLOCKED (waiting for subtasks to complete)
- no subtasks    → READY (existing behavior, unchanged)

This applies to both execute() and executeResume().

Adds ListSubtasks to the Store interface.

Tests:
- TestPool_Submit_TopLevel_WithSubtasks_GoesBlocked
- TestPool_Submit_TopLevel_NoSubtasks_GoesReady

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

1 files changed, 29 insertions, 6 deletions

diff --git a/internal/executor/executor.go b/internal/executor/executor.go
index baeb399..41377b2 100644
--- a/internal/executor/executor.go
+++ b/internal/executor/executor.go
@@ -20,6 +20,7 @@ import (
 type Store interface {
 	GetTask(id string) (*task.Task, error)
 	ListTasks(filter storage.TaskFilter) ([]*task.Task, error)
+	ListSubtasks(parentID string) ([]*task.Task, error)
 	ListExecutions(taskID string) ([]*storage.Execution, error)
 	CreateExecution(e *storage.Execution) error
 	UpdateExecution(e *storage.Execution) error
@@ -297,9 +298,20 @@ func (p *Pool) executeResume(ctx context.Context, t *task.Task, exec *storage.Ex
 		}
 	} else {
 		if t.ParentTaskID == "" {
-			exec.Status = "READY"
-			if err := p.store.UpdateTaskState(t.ID, task.StateReady); err != nil {
-				p.logger.Error("failed to update task state", "taskID", t.ID, "state", task.StateReady, "error", err)
+			subtasks, subErr := p.store.ListSubtasks(t.ID)
+			if subErr != nil {
+				p.logger.Error("failed to list subtasks", "taskID", t.ID, "error", subErr)
+			}
+			if subErr == nil && len(subtasks) > 0 {
+				exec.Status = "BLOCKED"
+				if err := p.store.UpdateTaskState(t.ID, task.StateBlocked); err != nil {
+					p.logger.Error("failed to update task state", "taskID", t.ID, "state", task.StateBlocked, "error", err)
+				}
+			} else {
+				exec.Status = "READY"
+				if err := p.store.UpdateTaskState(t.ID, task.StateReady); err != nil {
+					p.logger.Error("failed to update task state", "taskID", t.ID, "state", task.StateReady, "error", err)
+				}
 			}
 		} else {
 			exec.Status = "COMPLETED"
@@ -532,9 +544,20 @@ func (p *Pool) execute(ctx context.Context, t *task.Task) {
 		}
 	} else {
 		if t.ParentTaskID == "" {
-			exec.Status = "READY"
-			if err := p.store.UpdateTaskState(t.ID, task.StateReady); err != nil {
-				p.logger.Error("failed to update task state", "taskID", t.ID, "state", task.StateReady, "error", err)
+			subtasks, subErr := p.store.ListSubtasks(t.ID)
+			if subErr != nil {
+				p.logger.Error("failed to list subtasks", "taskID", t.ID, "error", subErr)
+			}
+			if subErr == nil && len(subtasks) > 0 {
+				exec.Status = "BLOCKED"
+				if err := p.store.UpdateTaskState(t.ID, task.StateBlocked); err != nil {
+					p.logger.Error("failed to update task state", "taskID", t.ID, "state", task.StateBlocked, "error", err)
+				}
+			} else {
+				exec.Status = "READY"
+				if err := p.store.UpdateTaskState(t.ID, task.StateReady); err != nil {
+					p.logger.Error("failed to update task state", "taskID", t.ID, "state", task.StateReady, "error", err)
+				}
 			}
 		} else {
 			exec.Status = "COMPLETED"