fix(crawler): harden crash & shutdown job recovery

Three failure-mode fixes surfaced by a crawler recovery audit:

- Graceful shutdown mid-dispatch now releases the in-flight job back to
  pending without burning a retry attempt. process_lease wraps the
  dispatch in a biased tokio::select! cancel arm that aborts the
  heartbeat and calls jobs::release; previously a mid-job SIGTERM left
  the row 'running' until lease expiry and cost one of max_attempts.

- Boot-time jobs::reclaim_orphaned resets 'running' jobs with an expired
  lease back to pending (attempt refunded), run once at daemon startup
  before workers start. Crash recovery is now immediate instead of
  waiting a full lease window for the lazy lease-expiry path. Safe under
  multi-replica: only already-expired leases are touched, which a
  healthy heartbeating peer never has.

- Manga-list parsing now warns when listing anchors are dropped for a
  missing/empty href or title (split into parse_manga_list_anchors so
  the drop count is testable), turning silent source markup drift into
  an observable signal. Returned refs are byte-identical to before.

Tests added: shutdown_mid_dispatch_releases_lease_without_burning_attempt,
reclaim_orphaned_resets_only_expired_running_jobs, and a drop-count unit
test. Patch bump 0.81.0 -> 0.81.1 (both manifests).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/crawler/source/target.rs

@@ -332,25 +332,54 @@ fn parse_manga_list_from(doc: &scraper::Html) -> Result<Vec<SourceMangaRef>, Pag
     if !has_logo_sentinel(doc) {
         return Err(PageError::transient("manga list: #logo sentinel missing"));
     }
+    let (refs, dropped) = parse_manga_list_anchors(doc);
+    // A non-zero drop count means the listing selector matched anchors but
+    // some lacked a usable href/title. In steady state this is ~always zero;
+    // a sustained non-zero count is the early signal of a source markup
+    // drift silently eroding coverage (GAP-2), so surface it rather than
+    // swallowing it in the filter. `#logo` was already confirmed present,
+    // so this is genuine per-item loss, not a broken-page response.
+    if dropped > 0 {
+        tracing::warn!(
+            dropped,
+            kept = refs.len(),
+            "manga list: dropped listing anchors with missing/empty href or title \
+             (possible source markup drift)"
+        );
+    }
+    Ok(refs)
+}
+
+/// Extract `SourceMangaRef`s from a listing document, returning the kept
+/// refs alongside the count of anchors dropped for a missing/empty href or
+/// title. Splitting the count out of [`parse_manga_list_from`] keeps the
+/// drop accounting unit-testable and lets the caller log coverage erosion.
+fn parse_manga_list_anchors(doc: &scraper::Html) -> (Vec<SourceMangaRef>, usize) {
     let sel = scraper::Selector::parse("#left_side .pic_list .updatesli span a").unwrap();
-    Ok(doc
-        .select(&sel)
-        .filter_map(|a| {
-            let url = a.value().attr("href")?.trim().to_string();
-            if url.is_empty() {
-                return None;
-            }
-            let title = collapse_whitespace(&a.text().collect::<String>());
-            if title.is_empty() {
-                return None;
-            }
-            Some(SourceMangaRef {
-                source_manga_key: derive_key_from_url(&url),
-                title,
-                url,
-            })
-        })
-        .collect())
+    let mut refs = Vec::new();
+    let mut dropped = 0usize;
+    for a in doc.select(&sel) {
+        let url = a
+            .value()
+            .attr("href")
+            .map(|h| h.trim().to_string())
+            .unwrap_or_default();
+        if url.is_empty() {
+            dropped += 1;
+            continue;
+        }
+        let title = collapse_whitespace(&a.text().collect::<String>());
+        if title.is_empty() {
+            dropped += 1;
+            continue;
+        }
+        refs.push(SourceMangaRef {
+            source_manga_key: derive_key_from_url(&url),
+            title,
+            url,
+        });
+    }
+    (refs, dropped)
 }
 
 fn parse_manga_detail(
@@ -699,6 +728,35 @@ mod tests {
         assert_eq!(refs[1].source_manga_key, "bar-baz");
     }
 
+    #[test]
+    fn parse_manga_list_anchors_reports_dropped_count() {
+        // The fixture's third `.updatesli` anchor has an empty href. The
+        // kept list must exclude it AND the drop count must be 1 so the
+        // caller can warn on markup drift (GAP-2).
+        let doc = scraper::Html::parse_document(LISTING_HTML);
+        let (refs, dropped) = parse_manga_list_anchors(&doc);
+        assert_eq!(refs.len(), 2, "two well-formed anchors kept");
+        assert_eq!(dropped, 1, "the empty-href anchor is counted as dropped");
+
+        // Also cover the *missing*-href branch (no `href` attr at all),
+        // which is the path the refactor reroutes through
+        // `.map(..).unwrap_or_default()` — distinct from the empty-string
+        // href above. Plus a missing-title anchor.
+        let html = r#"<html><body>
+            <header><div id="logo">Target</div></header>
+            <div id="left_side"><div class="pic_list">
+              <div class="updatesli"><span><a href="/manga/keep">Keep</a></span></div>
+              <div class="updatesli"><span><a>no href at all</a></span></div>
+              <div class="updatesli"><span><a href="/manga/blank">   </a></span></div>
+            </div></div>
+            </body></html>"#;
+        let doc = scraper::Html::parse_document(html);
+        let (refs, dropped) = parse_manga_list_anchors(&doc);
+        assert_eq!(refs.len(), 1, "only the well-formed anchor is kept");
+        assert_eq!(refs[0].title, "Keep");
+        assert_eq!(dropped, 2, "missing-href and missing-title anchors both counted");
+    }
+
     #[test]
     fn parse_manga_list_returns_transient_when_logo_missing() {
         // Broken-page response: no #logo, no listing. Empty Vec would