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>

2 files changed, 18 insertions, 0 deletions

diff --git a/internal/executor/executor.go b/internal/executor/executor.go
index bf209b7..475d150 100644
--- a/internal/executor/executor.go
+++ b/internal/executor/executor.go
@@ -28,6 +28,7 @@ type Store interface {
 	UpdateTaskQuestion(taskID, questionJSON string) error
 	UpdateTaskSummary(taskID, summary string) error
 	AppendTaskInteraction(taskID string, interaction task.Interaction) error
+	UpdateTaskAgent(id string, agent task.AgentConfig) error
 }
 
 // LogPather is an optional interface runners can implement to provide the log
@@ -435,6 +436,11 @@ func (p *Pool) execute(ctx context.Context, t *task.Task) {
 		}
 	}
 
+	// Persist the assigned agent (and model) to the database before running.
+	if err := p.store.UpdateTaskAgent(t.ID, t.Agent); err != nil {
+		p.logger.Error("failed to persist agent config", "error", err, "taskID", t.ID)
+	}
+
 	agentType := t.Agent.Type
 	if agentType == "" {
 		agentType = "claude"
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()