feat: persist agent assignment before task execution

- Add UpdateTaskAgent to Store interface and DB implementation
- Call UpdateTaskAgent in Pool.execute to persist assigned agent/model
  to database before the runner starts
- Update runTask in app.js to pass selected agent as query param

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

1 files changed, 12 insertions, 0 deletions

diff --git a/internal/storage/db.go b/internal/storage/db.go
index b8a7085..043009c 100644
--- a/internal/storage/db.go
+++ b/internal/storage/db.go
@@ -251,6 +251,18 @@ func (s *DB) ResetTaskForRetry(id string) (*task.Task, error) {
 	return t, nil
 }
 
+// UpdateTaskAgent updates only the agent configuration of a task.
+func (s *DB) UpdateTaskAgent(id string, agent task.AgentConfig) error {
+	configJSON, err := json.Marshal(agent)
+	if err != nil {
+		return fmt.Errorf("marshaling agent config: %w", err)
+	}
+	now := time.Now().UTC()
+	_, err = s.db.Exec(`UPDATE tasks SET config_json = ?, updated_at = ? WHERE id = ?`,
+		string(configJSON), now, id)
+	return err
+}
+
 // RejectTask sets a task's state to PENDING and stores the rejection comment.
 func (s *DB) RejectTask(id, comment string) error {
 	now := time.Now().UTC()