Tasks: poll start runs as a proper daemon

Phase 4 of the chain. Derives from design.md and testing-plan.md — each task's _Test:_ names a matrix row. Ticket: #191.

flowchart LR
  T1["1 · state paths"] --> T3["3 · heartbeat writer"]
  T1 --> T5["5 · --daemon / --logfile"]
  T1 --> T6["6 · poll status"]
  T2["2 · daemonize()"] --> T5
  T3 --> T4["4 · poller records a cycle"]
  T3 --> T6
  T5 --> T7["7 · control plane + daemon_entry"]
  T6 --> T7
  T4 --> T8["8 · integration tests"]
  T5 --> T8
  T6 --> T8
  T7 --> T9["9 · docs"]
  T8 --> T9
  T9 --> T10["10 · capability docs + decision"]

Tasks

• [x] 1. StateLayout grows the three poller paths. Add poll_pidfile, poll_status and poller_log; declare each in GENERATED_PATHS as local with its reason; replace the two ad-hoc <root>/poll.pid derivations (commands/poll.py, core/daemons.py) with the property. Requirements: R5.1, R5.2 · Test: T4

• [x] 2. the_loop/daemonize.py — detach, redirect, handshake.daemonize(logfile, timeout=60) (double-fork, setsid, dup2, reap the intermediate, no chdir) and notify_ready(). Pure stdlib; nothing poller-specific. Requirements: R1.1, R1.6, R2.1, R2.3, R3.4 · Test: T6

• [x] 3. the_loop/poller/heartbeat.py — write and read.PollHeartbeat.record(summary) (atomic tempfile + os.replace, warn-once on OSError) and PollHeartbeat.read(path) → Heartbeat | None. Requirements: R5.4, R4.5, R4.6 · Test: T1

• [x] 4. The poller records a heartbeat after every cycle. An optional heartbeat callable on Poller, invoked at the end of poll_once — so a --once run and a long-lived poller both leave one, and the poller core keeps no file handle of its own. Requirements: R4.5 · Test: T1, T6

• [x] 5. poll start gains --daemon / --foreground / --logfile. One dest, last-flag-wins; --daemon --once refused; the logfile opened and the lock probed before the fork, and the lock acquired (and a stale pidfile cleared) after it, on both the daemon and the foreground path; notify_ready() once the run loop is about to start; poller.started carries daemon and logfile. Requirements: R1.3, R1.4, R1.5, R2.2, R2.4, R3.1, R3.2, R3.3, R3.5 · Test: T3, T6

• [x] 6. poll status. New action: liveness from the lock, pid from the pidfile, the rest from the heartbeat; --format text|json; exit 0 running / 1 not; stale pidfile reported, not removed. Requirements: R4.1–R4.8 · Test: T2, T7

• [x] 7. The control plane starts daemons with a log, and reports the heartbeat.core/daemons.control_daemon("start") redirects stdout/stderr to the daemon's logfile instead of DEVNULL; daemon_status carries startedAt/lastCycleAt; daemon_entry forces args.daemon = False. Requirements: R2.5, R4.7 · Test: T5

• [x] 8. Integration tests against a real detached process.cli/tests/test_poll_daemon_integration.py, Gherkin-documented, one scenario per row of the T6 trace; each test kills what it spawned in a finally. Requirements: R1.1, R1.2, R2.1, R3.1, R3.3, R3.4, R3.5 · Test: T6, T7

• [x] 9. Documentation.docs/cli/commands/poll.md (the two flags, the status action, when to use which start mode, log rotation as the host's job), docs/cli/state.md (three classification rows, the .gitignore line) and the repository's own .gitignore. Requirements: R5.3 · Test: T4

• [x] 10. Capability docs and the decision record.docs/capabilities/cli.md (the poller's lifecycle), docs/decisions/decision-072.md (--daemon opt-in, not the default) plus its index row, and the execution log's ## Documentation section. Requirements: R1.3 (why the default did not move) · Test: T4 (docs parity)