fix(crawler): sentinel-gate parse_chapter_list to stop false drops (0.35.2)

parse_chapter_list previously returned Vec::new() on any selector
miss. The empty list flowed into sync_manga_chapters, whose soft-drop
branch then flipped every existing chapter's dropped_at to NOW().
Bookmarks subsequently pointed at dropped sources, and
enqueue_bookmarked_pending (filters on cs.dropped_at IS NULL) silently
stopped re-fetching pages.

Same shape as the walker race fixed in 0.35.1: a transient parse miss
masquerading as "source removed everything" → false soft-drop.

Fix: require #chapter_table in the DOM. Present-but-empty is preserved
as Ok(vec![]) so a freshly added manga with no published chapters
still parses cleanly. Absent table is now Transient — the job system
reschedules with backoff instead of treating the partial render as
data.

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

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.35.1"
+version = "0.35.2"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/crawler/source/target.rs

@@ -444,7 +444,7 @@ fn parse_manga_detail(
         .collect();
 
     let chapters = if include_chapters {
-        parse_chapter_list(&doc)
+        parse_chapter_list(&doc)?
     } else {
         Vec::new()
     };
@@ -502,9 +502,22 @@ fn strip_tag_count(s: &str) -> String {
     trimmed.to_string()
 }
 
-fn parse_chapter_list(doc: &scraper::Html) -> Vec<SourceChapterRef> {
+/// Parse the chapter table on a manga detail page. Returns `Transient` if
+/// `#chapter_table` isn't in the DOM at all — the table is required even
+/// for mangas with no published chapters yet (the source renders an empty
+/// `<table>`), so an absent table signals a partial render (post-load JS
+/// not done, layout drift) rather than a legitimately empty list. Without
+/// this sentinel, an empty `Vec` reaches `sync_manga_chapters` and the
+/// soft-drop branch flips every existing chapter to `dropped_at`.
+fn parse_chapter_list(doc: &scraper::Html) -> Result<Vec<SourceChapterRef>, PageError> {
+    if !has_chapter_table_sentinel(doc) {
+        return Err(PageError::transient(
+            "manga detail: #chapter_table sentinel missing",
+        ));
+    }
     let sel = scraper::Selector::parse("#chapter_table td h4 a.chico").unwrap();
-    doc.select(&sel)
+    Ok(doc
+        .select(&sel)
         .filter_map(|a| {
             let url = a.value().attr("href")?.trim().to_string();
             if url.is_empty() {
@@ -519,7 +532,16 @@ fn parse_chapter_list(doc: &scraper::Html) -> Vec<SourceChapterRef> {
                 url,
             })
         })
-        .collect()
+        .collect())
+}
+
+/// Returns true when the chapter-table container is present in the DOM.
+/// Source-specific: the target site uses `#chapter_table` as the wrapper
+/// element. Distinguishes "table is present but empty" (legit edge case
+/// for new mangas) from "table is missing entirely" (partial render).
+fn has_chapter_table_sentinel(doc: &scraper::Html) -> bool {
+    let sel = scraper::Selector::parse("#chapter_table").expect("valid selector");
+    doc.select(&sel).next().is_some()
 }
 
 fn parse_chapter_number(text: &str) -> Option<i32> {
@@ -880,7 +902,7 @@ mod tests {
             "../../../tests/fixtures/target/chapter_list_uu.html"
         );
         let doc = scraper::Html::parse_document(html);
-        let chapters = parse_chapter_list(&doc);
+        let chapters = parse_chapter_list(&doc).expect("fixture has the table");
 
         assert_eq!(chapters.len(), 15, "every row kept (notices/hiatus included)");
 
@@ -1027,9 +1049,17 @@ mod tests {
 
     #[test]
     fn missing_optional_fields_parse_to_none() {
+        // Minimal but well-formed detail page: title is required, every
+        // other field is optional, but the chapter table is structural —
+        // its absence is treated as Transient (a freshly added manga
+        // renders the table empty, not absent). See
+        // `parse_chapter_list_returns_transient_when_table_missing` for
+        // the negative case.
         let html = r#"<html><body>\
             <header><div id="logo">Target</div></header>\
-            <div class="w-title"><h1>Minimal</h1></div></body></html>"#;
+            <div class="w-title"><h1>Minimal</h1></div>\
+            <table id="chapter_table"></table>\
+            </body></html>"#;
         let m = parse_manga_detail(html, "min", true).unwrap();
         assert_eq!(m.title, "Minimal");
         assert!(m.summary.is_none());
@@ -1222,4 +1252,64 @@ mod tests {
         assert_eq!(displaced[0].source_manga_key, "X");
         assert_eq!(outcome, DisplacementOutcome::Shifted(1));
     }
+
+    #[test]
+    fn parse_chapter_list_returns_transient_when_table_missing() {
+        // Partial render (post-load JS hadn't injected the table, layout
+        // drift, etc). Returning Vec::new() would silently soft-drop every
+        // existing chapter for the manga via sync_manga_chapters; Transient
+        // is the signal the job system retries on.
+        let html = r#"<html><body>
+            <header><div id="logo">Target</div></header>
+            <div class="w-title"><h1>Test</h1></div>
+        </body></html>"#;
+        let doc = scraper::Html::parse_document(html);
+        let err = parse_chapter_list(&doc).expect_err("expected Transient");
+        assert!(err.is_transient(), "got non-transient: {err}");
+    }
+
+    #[test]
+    fn parse_chapter_list_ok_empty_when_table_present_but_no_rows() {
+        // A freshly-added manga with no chapters yet — the source renders
+        // the `<table id="chapter_table">` wrapper but no `<tr>` rows
+        // inside. Must stay distinguishable from a missing-table render.
+        let html = r#"<html><body>
+            <header><div id="logo">Target</div></header>
+            <table id="chapter_table"></table>
+        </body></html>"#;
+        let doc = scraper::Html::parse_document(html);
+        let chapters = parse_chapter_list(&doc).expect("present table is not transient");
+        assert!(chapters.is_empty());
+    }
+
+    #[test]
+    fn parse_manga_detail_propagates_chapter_table_transient() {
+        // End-to-end: a detail page that survives the #logo sentinel but
+        // has the chapter table stripped must fail Transient at the parser
+        // boundary, not return a SourceManga with empty chapters.
+        let html = r#"<html><body>
+            <header><div id="logo">Target</div></header>
+            <div class="w-title"><h1>Test Title</h1></div>
+            <div class="cover"><img src="/cover.jpg"></div>
+            <!-- intentionally no #chapter_table -->
+        </body></html>"#;
+        let err = parse_manga_detail(html, "key", true).expect_err("expected Transient");
+        assert!(err.is_transient(), "got non-transient: {err}");
+    }
+
+    #[test]
+    fn parse_manga_detail_skips_chapter_sentinel_when_include_chapters_false() {
+        // Metadata-only mode (`skip_chapters` upstream) must not require
+        // the chapter table — pipeline.rs avoids calling sync_manga_chapters
+        // for these mangas, so the absent table is not a correctness issue
+        // and shouldn't surface as Transient.
+        let html = r#"<html><body>
+            <header><div id="logo">Target</div></header>
+            <div class="w-title"><h1>Test Title</h1></div>
+            <div class="cover"><img src="/cover.jpg"></div>
+        </body></html>"#;
+        let manga = parse_manga_detail(html, "key", false)
+            .expect("metadata-only parse must not require chapter table");
+        assert!(manga.chapters.is_empty());
+    }
 }