fix(stage-engine): durable transition-ownership lease + expected-stage CAS (ORCH-114)

Close the root class of the ORCH-110/111/112/113 incident chain: side-effectful
stage transitions had no single ownership. `advance_stage` is re-enterable and wrote
the stage with a bare `UPDATE ... WHERE id=?` (no compare-and-swap), while >=5 actors
(monitor / Plane-webhook / reconciler F-1 / job-reaper / deploy-finalizer) enter the
same transition independently. A concurrent or post-restart re-entry therefore
re-applied irreversible effects (merge_pr / coverage-ratchet / image-rebuild /
prod-deploy initiation) and produced a contradictory rollback<->done (incident
ORCH-111, job 1914 / PR #130).

Two complementary layers, both additive, under one kill-switch, never-raise:
  1. Durable transition-lease (new table `transition_lease`) — owner-exclusion on
     ENTRY to the side-effectful region: a second actor that sees a LIVE owner does
     not start the heavy sub-gates at all (prevention, not post-hoc repair).
  2. Expected-stage CAS (`db.update_task_stage_cas`) — atomicity on the stage WRITE:
     a lost race aborts with NO side effect. Also closes the 6 paths that write the
     stage in bypass of advance_stage (gitea x5 + plane rollback).

Owner liveness = owner_pid + owner_boot_id (NOT a heartbeat — a blocking 900s merge
re-test cannot beat one; ADR-001 D3), making restart recovery free (a fresh boot_id
renders every prior lease stale -> reclaimed by recover_on_startup). The lease has no
own TTL: its hard age ceiling is the reaper Tier-3 backstop reaper_max_running_s, so
the cross-cutting budget invariant ORCH-065/109/110/113 is untouched.

Generalises ORCH-113 finalizer-liveness (process-local, Tier-2, deploy-staging) to a
durable cross-path lease: the reaper consults it on all relevant paths (defer live,
reclaim dead; Tier-3 ignores the marker -> bounded; a reap force-releases the lease);
reconciler F-1 and the Plane webhook defer on an active lease; main.lifespan calls
recover_on_startup() after requeue_running_jobs. finalizer_liveness.py is unchanged
(it remains the kill-switch-off fallback).

Scope self-hosting (transition_lease_repos="" -> orchestrator only; enduro untouched).
Kill-switch ORCH_TRANSITION_LEASE_ENABLED=false -> CAS degenerates to the prior
unconditional update_task_stage, lease inert, reaper -> ORCH-113 fallback (byte-for-
byte pre-ORCH-114). STAGE_TRANSITIONS / QG_CHECKS / check_* / machine-verdict keys /
existing table schemas — byte-for-byte (one additive table, no epoch column on tasks).

Observability: read-only `transition_lease` block in GET /queue + a Telegram alert on
forced/stale reclaim + optional POST /transition-lease/release?work_item=<id>.

Coverage: tests/test_orch114_transition_ownership.py (TC-01 mandatory regression of
the ORCH-111 class — red before fix, green after; TC-02..TC-14). Full suite green
(2048 passed); the 4 webhook tests that spied on the removed gitea.update_task_stage
were updated to spy on the new commit_stage_cas write path.

ADR: docs/work-items/ORCH-114/06-adr/ADR-001-transition-ownership-lease-and-stage-cas.md
Cross-cutting: docs/architecture/adr/adr-0045-transition-ownership-lease-and-stage-cas.md

Refs: ORCH-114
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/architecture/internals.md

@@ -188,6 +188,21 @@ CREATE TABLE events (
     payload TEXT,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 );
+
+-- ORCH-114 (adr-0045): durable transition-ownership lease. ОДНА аддитивная таблица
+-- (CREATE TABLE IF NOT EXISTS, паттерн repo_freeze/coverage_baseline/lessons) — одна
+-- строка = ≤1 активный владелец side-effectful перехода задачи. Живость владельца =
+-- owner_boot_id (нонс старта процесса; рестарт ⇒ смена ⇒ прежний lease мёртв) +
+-- pid_alive(owner_pid). БЕЗ epoch/version-колонки на tasks (стадия = версия CAS).
+CREATE TABLE transition_lease (
+    task_id       INTEGER PRIMARY KEY,
+    owner         TEXT NOT NULL,   -- monitor|reaper|reconciler|webhook|finalizer|engine
+    owner_pid     INTEGER,
+    owner_boot_id TEXT,
+    run_id        INTEGER,
+    stage         TEXT,            -- from-стадия захвата (контекст/наблюдаемость)
+    acquired_at   TEXT DEFAULT (datetime('now'))
+);
 ```
 
 ## Deployment
@@ -369,7 +384,13 @@ status='queued'` и проверяет `rowcount`. При гонке двух т
 
 В `main.py` lifespan **после** M-1 orphan-recovery вызывается `requeue_running_jobs()`:
 jobs со статусом `running` (воркер умёр на рестарте) → возвращаются в `queued`.
-Потом стартует воркер; на shutdown — `worker.stop()` (Event.set + join).
+**ORCH-114 (adr-0045):** сразу следом вызывается `transition_lease.recover_on_startup()` —
+новый процесс имеет свежий `boot_id`, поэтому ВСЕ записанные ранее `transition_lease`
+устарели (boot-id mismatch) → реклеймятся, и только что requeued-jobs переисполняют свои
+side-effectful переходы **последовательно** (один владелец), без двойного необратимого
+эффекта. Идемпотентность самого re-drive обеспечивают существующие авторитетные факты
+(SHA-in-main ORCH-071/073, маркер `INITIATED` ORCH-036, coverage-ratchet CAS ORCH-027) —
+НЕ новый recovery-мозг. Потом стартует воркер; на shutdown — `worker.stop()` (Event.set + join).
 
 ### Job-reaper (ORCH-065, рестарт НЕ требуется)