fix(crawler): skip sync when empty chapters + prior > 0 (0.36.6)

The wait_for_selector wait in 0.36.2 narrows the partial-render race
window but doesn't close it: a render that takes longer than
SELECTOR_TIMEOUT (10s) still hands an empty Vec to sync_manga_chapters,
and the soft-drop branch flips every existing chapter to dropped_at.
The next tick recovers but a manga's reader briefly stops working in
between.

Close it at the pipeline level. Between fetch_manga and the upsert/
sync, if the parsed chapter list is empty and the prior live count
for (source_id, source_manga_key) is > 0, treat the fetch as a
transient failure: log, bump mangas_failed, skip upsert + sync + the
seen.insert so a later batch / tick retries. Brand-new mangas with
genuinely zero chapters (prior == 0) pass through unchanged.

New repo helper repo::crawler::live_chapter_count_for_source_manga
joins chapters → chapter_sources → manga_sources with dropped_at IS
NULL — same lockstep as dispatch_target and the enqueue queries.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1470,7 +1470,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.36.5"
+version = "0.36.6"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.36.5"
+version = "0.36.6"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/crawler/pipeline.rs

@@ -215,6 +215,48 @@ pub async fn run_metadata_pass(
                 }
             };
 
+            // Partial-render guard: an empty chapter list paired with a
+            // prior count > 0 is overwhelmingly a chromium snapshot
+            // taken between the #chapter_table wrapper render and its
+            // rows render. The wait_for_selector wait in `navigate`
+            // narrows this window but cannot close it for slow renders
+            // beyond the selector budget. Treat as a transient failure
+            // here — skip upsert, skip seen.insert — so the next batch
+            // (or the next tick) retries. Skipped in `skip_chapters`
+            // mode because the parser is configured to return an empty
+            // Vec by design there.
+            if !skip_chapters && manga.chapters.is_empty() {
+                match repo::crawler::live_chapter_count_for_source_manga(
+                    db, source_id, &r.source_manga_key,
+                )
+                .await
+                {
+                    Ok(prior) if prior > 0 => {
+                        tracing::warn!(
+                            key = %r.source_manga_key,
+                            url = %r.url,
+                            prior_chapter_count = prior,
+                            "fetch_manga returned empty chapters but prior count > 0; treating as partial-render transient and skipping"
+                        );
+                        stats.mangas_failed += 1;
+                        continue;
+                    }
+                    Ok(_) => {}
+                    Err(e) => {
+                        // DB lookup failed — fail safe: skip rather
+                        // than risk a soft-drop on a manga whose prior
+                        // count we couldn't confirm.
+                        tracing::warn!(
+                            key = %r.source_manga_key,
+                            error = ?e,
+                            "live_chapter_count_for_source_manga failed; skipping cautiously"
+                        );
+                        stats.mangas_failed += 1;
+                        continue;
+                    }
+                }
+            }
+
             let upsert = match repo::crawler::upsert_manga_from_source(
                 db, source_id, &r.url, &manga,
             )

backend/src/repo/crawler.rs

@@ -458,6 +458,44 @@ pub async fn sync_manga_chapters(
     Ok(diff)
 }
 
+/// Count the chapters that the source `(source_id, source_manga_key)`
+/// is currently known to attach to — i.e. the number of `chapter_sources`
+/// rows for the manga identified by the (source_id, source_manga_key)
+/// pair, restricted to live (`dropped_at IS NULL`) rows.
+///
+/// Used by the metadata pass's partial-render guard: if `fetch_manga`
+/// returns an empty `chapters` Vec but the source previously surfaced
+/// chapters here, that's most likely a chromium snapshot taken between
+/// the `#chapter_table` wrapper render and its rows render — the
+/// safest move is to skip `sync_manga_chapters` so the soft-drop
+/// branch doesn't flip every existing chapter to `dropped_at`.
+///
+/// Returns `Ok(0)` when the manga is brand-new (no `manga_sources`
+/// row yet), which is the legitimate "this manga has no chapters yet"
+/// case and must NOT be flagged.
+pub async fn live_chapter_count_for_source_manga(
+    pool: &PgPool,
+    source_id: &str,
+    source_manga_key: &str,
+) -> sqlx::Result<i64> {
+    let row: Option<(i64,)> = sqlx::query_as(
+        "SELECT COUNT(*) \
+           FROM chapter_sources cs \
+           JOIN chapters c ON c.id = cs.chapter_id \
+           JOIN manga_sources ms \
+             ON ms.manga_id = c.manga_id \
+            AND ms.source_id = cs.source_id \
+          WHERE ms.source_id = $1 \
+            AND ms.source_manga_key = $2 \
+            AND cs.dropped_at IS NULL",
+    )
+    .bind(source_id)
+    .bind(source_manga_key)
+    .fetch_optional(pool)
+    .await?;
+    Ok(row.map(|(n,)| n).unwrap_or(0))
+}
+
 /// Mark a metadata pass as in-flight for `source_id`. Stamps
 /// `last_run_completed:<source_id>` in `crawler_state` with
 /// `{"completed": false, "at": now}`. A crash, panic, or SIGKILL after

backend/tests/crawler_sync.rs

@@ -232,6 +232,67 @@ async fn sync_chapters_adds_new_refreshes_existing_and_drops_vanished(pool: PgPo
     assert!(dropped.0.is_some(), "ch2 should be soft-dropped");
 }
 
+#[sqlx::test(migrations = "./migrations")]
+async fn live_chapter_count_returns_zero_for_unknown_source_key(pool: PgPool) {
+    crawler::ensure_source(&pool, "target", "T", "https://x.example")
+        .await
+        .unwrap();
+    // No manga_sources row yet → unknown key path. Must not error and
+    // must report zero so the partial-render guard accepts the
+    // "brand-new manga with no chapters" case as legitimate.
+    let n = crawler::live_chapter_count_for_source_manga(&pool, "target", "nobody")
+        .await
+        .unwrap();
+    assert_eq!(n, 0);
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn live_chapter_count_only_counts_live_sources(pool: PgPool) {
+    crawler::ensure_source(&pool, "target", "T", "https://x.example")
+        .await
+        .unwrap();
+    let m = sample_manga("foo", "Foo Manga", "hash-1");
+    let up = crawler::upsert_manga_from_source(&pool, "target", "https://x.example/foo", &m)
+        .await
+        .unwrap();
+    let chapters = vec![
+        SourceChapterRef {
+            source_chapter_key: "1".into(),
+            number: 1,
+            title: Some("Ch.1".into()),
+            url: "https://x.example/foo/1".into(),
+        },
+        SourceChapterRef {
+            source_chapter_key: "2".into(),
+            number: 2,
+            title: Some("Ch.2".into()),
+            url: "https://x.example/foo/2".into(),
+        },
+    ];
+    crawler::sync_manga_chapters(&pool, "target", up.manga_id, &chapters)
+        .await
+        .unwrap();
+    assert_eq!(
+        crawler::live_chapter_count_for_source_manga(&pool, "target", "foo")
+            .await
+            .unwrap(),
+        2
+    );
+    // Soft-drop one source row — count drops by one, the row stays.
+    sqlx::query(
+        "UPDATE chapter_sources SET dropped_at = NOW() WHERE source_chapter_key = '2'",
+    )
+    .execute(&pool)
+    .await
+    .unwrap();
+    assert_eq!(
+        crawler::live_chapter_count_for_source_manga(&pool, "target", "foo")
+            .await
+            .unwrap(),
+        1
+    );
+}
+
 /// Real-world sources publish multiple chapters at the same number
 /// (different uploaders, translator notes, re-releases). After the
 /// (manga_id, number) UNIQUE drop in 0013, each `SourceChapterRef`

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.36.5",
+  "version": "0.36.6",
   "private": true,
   "type": "module",
   "scripts": {