feat: blocked task state for agent questions via session resume

When an agent needs user input it writes a question to
$CLAUDOMATOR_QUESTION_FILE and exits. The runner detects the file and
returns BlockedError; the pool transitions the task to BLOCKED and
stores the question JSON on the task record.

The user answers via POST /api/tasks/{id}/answer. The server looks up
the claude session_id from the most recent execution and submits a
resume execution (claude --resume <session-id> "<answer>"), freeing the
executor slot entirely while waiting.

Changes:
- task: add StateBlocked, transitions RUNNING→BLOCKED, BLOCKED→QUEUED
- storage: add session_id to executions, question_json to tasks;
  add GetLatestExecution and UpdateTaskQuestion methods
- executor: BlockedError type; ClaudeRunner pre-assigns --session-id,
  sets CLAUDOMATOR_QUESTION_FILE env var, detects question file on exit;
  buildArgs handles --resume mode; Pool.SubmitResume for resume path
- api: handleAnswerQuestion rewritten to create resume execution
- preamble: add question protocol instructions for agents
- web: BLOCKED state badge (indigo), question text + option buttons or
  free-text input with Submit on the task card footer

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

1 files changed, 35 insertions, 10 deletions

diff --git a/internal/storage/db.go b/internal/storage/db.go
index e656f98..0e4d6f1 100644
--- a/internal/storage/db.go
+++ b/internal/storage/db.go
@@ -88,6 +88,8 @@ func (s *DB) migrate() error {
 	migrations := []string{
 		`ALTER TABLE tasks ADD COLUMN parent_task_id TEXT`,
 		`ALTER TABLE tasks ADD COLUMN rejection_comment TEXT`,
+		`ALTER TABLE tasks ADD COLUMN question_json TEXT`,
+		`ALTER TABLE executions ADD COLUMN session_id TEXT`,
 	}
 	for _, m := range migrations {
 		if _, err := s.db.Exec(m); err != nil {
@@ -136,13 +138,13 @@ func (s *DB) CreateTask(t *task.Task) error {
 
 // GetTask retrieves a task by ID.
 func (s *DB) GetTask(id string) (*task.Task, error) {
-	row := s.db.QueryRow(`SELECT id, name, description, config_json, priority, timeout_ns, retry_json, tags_json, depends_on_json, parent_task_id, state, created_at, updated_at, rejection_comment FROM tasks WHERE id = ?`, id)
+	row := s.db.QueryRow(`SELECT id, name, description, config_json, priority, timeout_ns, retry_json, tags_json, depends_on_json, parent_task_id, state, created_at, updated_at, rejection_comment, question_json FROM tasks WHERE id = ?`, id)
 	return scanTask(row)
 }
 
 // ListTasks returns tasks matching the given filter.
 func (s *DB) ListTasks(filter TaskFilter) ([]*task.Task, error) {
-	query := `SELECT id, name, description, config_json, priority, timeout_ns, retry_json, tags_json, depends_on_json, parent_task_id, state, created_at, updated_at, rejection_comment FROM tasks WHERE 1=1`
+	query := `SELECT id, name, description, config_json, priority, timeout_ns, retry_json, tags_json, depends_on_json, parent_task_id, state, created_at, updated_at, rejection_comment, question_json FROM tasks WHERE 1=1`
 	var args []interface{}
 
 	if filter.State != "" {
@@ -174,7 +176,7 @@ func (s *DB) ListTasks(filter TaskFilter) ([]*task.Task, error) {
 
 // ListSubtasks returns all tasks whose parent_task_id matches the given ID.
 func (s *DB) ListSubtasks(parentID string) ([]*task.Task, error) {
-	rows, err := s.db.Query(`SELECT id, name, description, config_json, priority, timeout_ns, retry_json, tags_json, depends_on_json, parent_task_id, state, created_at, updated_at, rejection_comment FROM tasks WHERE parent_task_id = ? ORDER BY created_at ASC`, parentID)
+	rows, err := s.db.Query(`SELECT id, name, description, config_json, priority, timeout_ns, retry_json, tags_json, depends_on_json, parent_task_id, state, created_at, updated_at, rejection_comment, question_json FROM tasks WHERE parent_task_id = ? ORDER BY created_at ASC`, parentID)
 	if err != nil {
 		return nil, err
 	}
@@ -308,28 +310,33 @@ type Execution struct {
 	ArtifactDir string
 	CostUSD     float64
 	ErrorMsg    string
+	SessionID   string // claude --session-id; persisted for resume
+
+	// In-memory only: set when creating a resume execution, not stored in DB.
+	ResumeSessionID string
+	ResumeAnswer    string
 }
 
 // CreateExecution inserts an execution record.
 func (s *DB) CreateExecution(e *Execution) error {
 	_, err := s.db.Exec(`
-		INSERT INTO executions (id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg)
-		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		INSERT INTO executions (id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg, session_id)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
 		e.ID, e.TaskID, e.StartTime.UTC(), e.EndTime.UTC(), e.ExitCode, e.Status,
-		e.StdoutPath, e.StderrPath, e.ArtifactDir, e.CostUSD, e.ErrorMsg,
+		e.StdoutPath, e.StderrPath, e.ArtifactDir, e.CostUSD, e.ErrorMsg, e.SessionID,
 	)
 	return err
 }
 
 // GetExecution retrieves an execution by ID.
 func (s *DB) GetExecution(id string) (*Execution, error) {
-	row := s.db.QueryRow(`SELECT id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg FROM executions WHERE id = ?`, id)
+	row := s.db.QueryRow(`SELECT id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg, session_id FROM executions WHERE id = ?`, id)
 	return scanExecution(row)
 }
 
 // ListExecutions returns executions for a task.
 func (s *DB) ListExecutions(taskID string) ([]*Execution, error) {
-	rows, err := s.db.Query(`SELECT id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg FROM executions WHERE task_id = ? ORDER BY start_time DESC`, taskID)
+	rows, err := s.db.Query(`SELECT id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg, session_id FROM executions WHERE task_id = ? ORDER BY start_time DESC`, taskID)
 	if err != nil {
 		return nil, err
 	}
@@ -346,6 +353,20 @@ func (s *DB) ListExecutions(taskID string) ([]*Execution, error) {
 	return execs, rows.Err()
 }
 
+// GetLatestExecution returns the most recent execution for a task.
+func (s *DB) GetLatestExecution(taskID string) (*Execution, error) {
+	row := s.db.QueryRow(`SELECT id, task_id, start_time, end_time, exit_code, status, stdout_path, stderr_path, artifact_dir, cost_usd, error_msg, session_id FROM executions WHERE task_id = ? ORDER BY start_time DESC LIMIT 1`, taskID)
+	return scanExecution(row)
+}
+
+// UpdateTaskQuestion stores the pending question JSON on a task.
+// Pass empty string to clear the question after it has been answered.
+func (s *DB) UpdateTaskQuestion(taskID, questionJSON string) error {
+	_, err := s.db.Exec(`UPDATE tasks SET question_json = ?, updated_at = ? WHERE id = ?`,
+		questionJSON, time.Now().UTC(), taskID)
+	return err
+}
+
 // UpdateExecution updates a completed execution.
 func (s *DB) UpdateExecution(e *Execution) error {
 	_, err := s.db.Exec(`
@@ -374,10 +395,12 @@ func scanTask(row scanner) (*task.Task, error) {
 		timeoutNS        int64
 		parentTaskID     sql.NullString
 		rejectionComment sql.NullString
+		questionJSON     sql.NullString
 	)
-	err := row.Scan(&t.ID, &t.Name, &t.Description, &configJSON, &priority, &timeoutNS, &retryJSON, &tagsJSON, &depsJSON, &parentTaskID, &state, &t.CreatedAt, &t.UpdatedAt, &rejectionComment)
+	err := row.Scan(&t.ID, &t.Name, &t.Description, &configJSON, &priority, &timeoutNS, &retryJSON, &tagsJSON, &depsJSON, &parentTaskID, &state, &t.CreatedAt, &t.UpdatedAt, &rejectionComment, &questionJSON)
 	t.ParentTaskID = parentTaskID.String
 	t.RejectionComment = rejectionComment.String
+	t.QuestionJSON = questionJSON.String
 	if err != nil {
 		return nil, err
 	}
@@ -405,11 +428,13 @@ func scanTaskRows(rows *sql.Rows) (*task.Task, error) {
 
 func scanExecution(row scanner) (*Execution, error) {
 	var e Execution
+	var sessionID sql.NullString
 	err := row.Scan(&e.ID, &e.TaskID, &e.StartTime, &e.EndTime, &e.ExitCode, &e.Status,
-		&e.StdoutPath, &e.StderrPath, &e.ArtifactDir, &e.CostUSD, &e.ErrorMsg)
+		&e.StdoutPath, &e.StderrPath, &e.ArtifactDir, &e.CostUSD, &e.ErrorMsg, &sessionID)
 	if err != nil {
 		return nil, err
 	}
+	e.SessionID = sessionID.String
 	return &e, nil
 }