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, 4 insertions, 1 deletions

diff --git a/internal/task/task.go b/internal/task/task.go
index 3e74a82..587993f 100644
--- a/internal/task/task.go
+++ b/internal/task/task.go
@@ -14,6 +14,7 @@ const (
 	StateTimedOut      State = "TIMED_OUT"
 	StateCancelled     State = "CANCELLED"
 	StateBudgetExceeded State = "BUDGET_EXCEEDED"
+	StateBlocked        State = "BLOCKED"
 )
 
 type Priority string
@@ -56,6 +57,7 @@ type Task struct {
 	DependsOn   []string     `yaml:"depends_on" json:"depends_on"`
 	State             State        `yaml:"-"          json:"state"`
 	RejectionComment  string       `yaml:"-"          json:"rejection_comment,omitempty"`
+	QuestionJSON      string       `yaml:"-"          json:"question,omitempty"`
 	CreatedAt         time.Time    `yaml:"-"          json:"created_at"`
 	UpdatedAt         time.Time    `yaml:"-"          json:"updated_at"`
 }
@@ -92,10 +94,11 @@ func ValidTransition(from, to State) bool {
 	transitions := map[State][]State{
 		StatePending:   {StateQueued, StateCancelled},
 		StateQueued:    {StateRunning, StateCancelled},
-		StateRunning:   {StateReady, StateCompleted, StateFailed, StateTimedOut, StateCancelled, StateBudgetExceeded},
+		StateRunning:   {StateReady, StateCompleted, StateFailed, StateTimedOut, StateCancelled, StateBudgetExceeded, StateBlocked},
 		StateReady:     {StateCompleted, StatePending},
 		StateFailed:    {StateQueued}, // retry
 		StateTimedOut:  {StateQueued}, // retry
+		StateBlocked:   {StateQueued}, // answer received → re-queue as resume execution
 	}
 	for _, allowed := range transitions[from] {
 		if allowed == to {