fix(jobs): per-lease generation token closes the ack-from-dead-lease race (0.87.26)

0.87.20 narrowed but did not close the force-analyze race:
ack_done / ack_failed / renew matched only on (id, state='running'),
so a worker A whose lease was released mid-flight (force-analyze,
reclaim_orphaned) could still come back later — once a successor B
re-leased the same id and put it back to state='running' — and
clobber B's lease. A's stale result became the row's `done` payload;
B's in-flight work was silently lost. The pre-existing test even
documented this hole: "We can't make ack_done's lease_id distinguish
A from B today".

Add `lease_generation BIGINT NOT NULL DEFAULT 0` to crawler_jobs
(migration 0032). It is bumped by every lease, release / release_unowned,
and reclaim_orphaned, so lease identity is `(id, generation)` rather
than just `id`. Each Lease struct carries its generation. ack_done /
ack_failed / renew / release match on `(id, generation, state='running')`
so a stale ack from a prior generation finds zero rows and falls
back to the existing warn-and-skip branch.

Split the release surface in two:
  * release(lease_id, lease_generation) — owner-aware path for
    workers (graceful shutdown, session-expired), matches the
    caller's specific lease.
  * release_unowned(lease_id) — id-only path for force-analyze and
    ops tools that drop a running lease without holding a Lease
    struct; unconditionally bumps generation so any pending ack
    from the in-flight original becomes a no-op.

Force-analyze in repo::page_analysis now uses release_unowned; the
test in api_admin_analysis still passes unchanged (it only asserts
the steady-state outcome). The pre-existing `ack_done_no_ops_when_
lease_was_stolen` test is strengthened: it now mints both A and B
leases, asserts their generations differ, and verifies A's stale
ack does NOT clobber B's running row — the assertion the old test
explicitly couldn't make.

Five new tests in tests/crawler_jobs.rs pin every facet:
  * lease_assigns_strictly_increasing_generation_per_release
  * ack_done_from_dead_lease_after_release_unowned_is_a_no_op
  * ack_failed_from_dead_lease_after_release_unowned_is_a_no_op
  * renew_from_dead_lease_is_a_no_op
  * release_unowned_bumps_generation_even_when_lease_is_held

Mutation-confirmed: relaxing the ack_done guard to
`lease_generation >= $2` (bind 0) makes the race test fail with
state=done — the exact prior-bug shape.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/crawler/daemon.rs

@@ -404,7 +404,7 @@ impl WorkerContext {
                 .ok()
                 .flatten();
             if matches!(page_count, Some(n) if n > 0) {
-                let _ = jobs::ack_done(&self.pool, lease.id).await;
+                let _ = jobs::ack_done(&self.pool, lease.id, lease.lease_generation).await;
                 return;
             }
         }
@@ -416,10 +416,11 @@ impl WorkerContext {
         let heartbeat = {
             let hb_pool = self.pool.clone();
             let hb_id = lease.id;
+            let hb_gen = lease.lease_generation;
             tokio::spawn(async move {
                 loop {
                     tokio::time::sleep(LEASE_HEARTBEAT).await;
-                    match jobs::renew(&hb_pool, hb_id, LEASE_DURATION).await {
+                    match jobs::renew(&hb_pool, hb_id, hb_gen, LEASE_DURATION).await {
                         Ok(true) => {}
                         Ok(false) => break,
                         Err(e) => {
@@ -453,7 +454,7 @@ impl WorkerContext {
                 // branch here, so a mid-dispatch SIGTERM left the row `running`
                 // until lease expiry and cost one attempt.
                 heartbeat.abort();
-                let _ = jobs::release(&self.pool, lease.id).await;
+                let _ = jobs::release(&self.pool, lease.id, lease.lease_generation).await;
                 tracing::info!(
                     worker = self.id,
                     lease_id = %lease.id,
@@ -480,6 +481,7 @@ impl WorkerContext {
                     "dispatch timed out",
                     lease.attempts,
                     lease.max_attempts,
+                    lease.lease_generation,
                 )
                 .await;
                 return;
@@ -487,7 +489,7 @@ impl WorkerContext {
         };
         match outcome {
             Ok(Ok(SyncOutcome::Fetched { .. } | SyncOutcome::Skipped)) => {
-                let _ = jobs::ack_done(&self.pool, lease.id).await;
+                let _ = jobs::ack_done(&self.pool, lease.id, lease.lease_generation).await;
             }
             Ok(Ok(SyncOutcome::SessionExpired)) => {
                 tracing::error!(
@@ -498,7 +500,7 @@ impl WorkerContext {
                 self.session_expired.store(true, Ordering::Release);
                 // Push the session-expired flip to live status subscribers.
                 self.status.poke();
-                let _ = jobs::release(&self.pool, lease.id).await;
+                let _ = jobs::release(&self.pool, lease.id, lease.lease_generation).await;
             }
             Ok(Err(e)) => {
                 tracing::warn!(
@@ -513,6 +515,7 @@ impl WorkerContext {
                     &format!("{e:#}"),
                     lease.attempts,
                     lease.max_attempts,
+                    lease.lease_generation,
                 )
                 .await;
             }
@@ -528,6 +531,7 @@ impl WorkerContext {
                     "worker panicked",
                     lease.attempts,
                     lease.max_attempts,
+                    lease.lease_generation,
                 )
                 .await;
             }