Task lifecycle

                 ┌─────────────┐
                 │   CREATED   │  agent called await_human()
                 └──────┬──────┘
                        │ notify channels (slack, email, …)
                        ▼
                 ┌─────────────┐
                 │  NOTIFIED   │  message posted, awaiting human
                 └──────┬──────┘
                        │ human opens in dashboard / slack / email
                        ▼
                 ┌─────────────┐
                 │ IN_PROGRESS │  (optional intermediate)
                 └──────┬──────┘
                        │ human submits
                        ▼
              ┌──────────┴──────────┐
              │                     │
              ▼ verifier passes     ▼ verifier rejects
       ┌──────────────┐      ┌─────────────┐
       │  COMPLETED   │      │  REJECTED   │  ← non-terminal
       └──────────────┘      └──────┬──────┘     (human gets to retry)
        terminal                    │
                                    │ exhausts max_attempts
                                    ▼
                         ┌─────────────────────────┐
                         │ VERIFICATION_EXHAUSTED  │
                         └─────────────────────────┘
                                  terminal


Side branches:

  any non-terminal status ──▶  TIMED_OUT   (scheduler hit `timeout_at`)
  any non-terminal status ──▶  CANCELLED   (agent or operator cancelled)

try:
    decision = await_human_sync(...)        # blocks until terminal
    # status was COMPLETED → decision is the typed response
except TaskTimeoutError:
    # status was TIMED_OUT
except TaskCancelledError:
    # status was CANCELLED
except VerificationExhaustedError:
    # status was VERIFICATION_EXHAUSTED