fix: interleave uploaded chapters by number in the chapter list

Uploaded chapters have no source_index, and ORDER BY source_index DESC NULLS
LAST sorted every one of them after all crawled chapters regardless of number
— an uploaded chapter 5 landed after crawled chapter 100. Slot each uploaded
chapter by number, just before the crawled chapter with the smallest greater
number, so it interleaves. Crawled rows keep their reversed source-DOM order,
preserving the deliberate placement of non-numeric entries (migration 0021).

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

backend/Cargo.lock

@@ -1558,7 +1558,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.124.21"
+version = "0.124.22"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.124.21"
+version = "0.124.22"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/repo/chapter.rs

@@ -12,14 +12,19 @@ pub async fn list_for_manga(
     limit: i64,
     offset: i64,
 ) -> AppResult<Vec<Chapter>> {
-    // Display order = source-site order reversed. The crawler stamps
+    // Display order. Crawled chapters carry `source_index` = position in the
-    // `source_index` = position in the source DOM (0 = first = newest
+    // source DOM (0 = newest on this site, migration 0021); we display them
-    // on this site, see migration 0021), so DESC puts the oldest
+    // reversed (oldest first) via the `-source_index` key, which keeps the
-    // chapter first and keeps the site's variant grouping and the
+    // site's variant grouping and non-numeric entries (e.g. "notice.") in the
-    // placement of non-numeric entries (e.g. "notice. : Officials")
+    // spot the site placed them — NOT clustered at number 0.
-    // intact. NULLS LAST keeps user-uploaded chapters (no source row)
+    //
-    // and rows that pre-date the migration below crawled rows; the
+    // User-uploaded chapters have no `source_index`. Instead of dumping them
-    // (number, created_at) tail then orders them deterministically.
+    // after every crawled chapter (the old `NULLS LAST` bug, which put an
+    // uploaded chapter 5 after crawled chapter 100), each is slotted by NUMBER:
+    // just before the crawled chapter with the smallest number greater than it,
+    // so it interleaves. An upload newer than every crawled chapter goes last;
+    // when there are no crawled chapters at all, uploads fall back to the
+    // `number, created_at` tail.
     let rows = sqlx::query_as::<_, Chapter>(
         r#"
         SELECT id, manga_id, number, title, page_count, created_at,
@@ -31,7 +36,22 @@ pub async fn list_for_manga(
                   FROM pages p WHERE p.chapter_id = chapters.id)::bigint AS size_bytes
         FROM chapters
         WHERE manga_id = $1
-        ORDER BY source_index DESC NULLS LAST, number ASC, created_at ASC
+        ORDER BY
+            CASE
+                WHEN source_index IS NOT NULL THEN (-source_index)::float8
+                ELSE COALESCE(
+                    (SELECT MIN(-c2.source_index)::float8 - 0.5
+                       FROM chapters c2
+                      WHERE c2.manga_id = chapters.manga_id
+                        AND c2.source_index IS NOT NULL
+                        AND c2.number > chapters.number),
+                    (SELECT COALESCE(MAX(-c3.source_index), 0)::float8 + 0.5
+                       FROM chapters c3
+                      WHERE c3.manga_id = chapters.manga_id
+                        AND c3.source_index IS NOT NULL)
+                )
+            END,
+            number ASC, created_at ASC
         LIMIT $2 OFFSET $3
         "#,
     )

backend/tests/api_chapters.rs

@@ -148,6 +148,49 @@ async fn list_chapters_returned_in_number_order(pool: PgPool) {
     assert_eq!(body["items"][1]["title"], serde_json::Value::Null);
 }
 
+#[sqlx::test(migrations = "./migrations")]
+async fn list_interleaves_uploaded_and_crawled_chapters_by_number(pool: PgPool) {
+    // Mixed source: crawled chapters carry a `source_index`; an uploaded
+    // chapter has none. The uploaded chapter must interleave by NUMBER, not sort
+    // after every crawled chapter (the old `source_index DESC NULLS LAST` bug
+    // dumped uploaded chapter 2 to the end, giving [1, 3, 2]).
+    let h = common::harness(pool.clone());
+    let (_, cookie) = common::register_user(&h.app).await;
+    let manga_id = seed_manga(&h, &cookie, "Berserk").await;
+
+    // Two crawled chapters (1 and 3) with DOM positions — newest-first, so
+    // chapter 3 is at source_index 0 and chapter 1 at source_index 1.
+    let c1 = seed_chapter(&pool, manga_id, 1, Some("Crawled One")).await;
+    let c3 = seed_chapter(&pool, manga_id, 3, Some("Crawled Three")).await;
+    sqlx::query("UPDATE chapters SET source_index = 1 WHERE id = $1")
+        .bind(c1)
+        .execute(&pool)
+        .await
+        .unwrap();
+    sqlx::query("UPDATE chapters SET source_index = 0 WHERE id = $1")
+        .bind(c3)
+        .execute(&pool)
+        .await
+        .unwrap();
+    // Uploaded chapter 2 — no source_index.
+    seed_chapter(&pool, manga_id, 2, Some("Uploaded Two")).await;
+
+    let resp = h
+        .app
+        .oneshot(common::get(&format!("/api/v1/mangas/{manga_id}/chapters")))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    let body = common::body_json(resp).await;
+    let numbers: Vec<i64> = body["items"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .map(|c| c["number"].as_i64().unwrap())
+        .collect();
+    assert_eq!(numbers, vec![1, 2, 3], "uploaded chapter 2 must slot between 1 and 3");
+}
+
 #[sqlx::test(migrations = "./migrations")]
 async fn list_chapters_returns_404_for_unknown_manga(pool: PgPool) {
     let h = common::harness(pool);

backend/tests/crawler_sync.rs

@@ -1175,7 +1175,7 @@ async fn list_for_manga_returns_source_order_reversed(pool: PgPool) {
 }
 
 #[sqlx::test(migrations = "./migrations")]
-async fn list_for_manga_places_null_source_index_last(pool: PgPool) {
+async fn list_for_manga_interleaves_null_source_index_by_number(pool: PgPool) {
     crawler::ensure_source(&pool, "target", "T", "https://x.example")
         .await
         .unwrap();
@@ -1184,23 +1184,24 @@ async fn list_for_manga_places_null_source_index_last(pool: PgPool) {
         .await
         .unwrap();
 
-    // Crawled chapters get source_index 0 and 1; the upload path leaves
+    // Crawled chapters, newest-first in the source DOM (so chapter 3 is at
-    // it NULL. NULLS LAST plus the (number, created_at) tail means the
+    // source_index 0 and chapter 1 at source_index 1). Reversed for display that
-    // upload sits after both crawled rows even though its number is in
+    // is [Ch.1, Ch.3]. The uploaded chapter 2 must slot BETWEEN them by number,
-    // the middle.
+    // not fall to the end — that was the bug (NULLS LAST dumped it last
+    // regardless of its number).
     let crawled = vec![
-        SourceChapterRef {
-            source_chapter_key: "a".into(),
-            number: 1,
-            title: Some("Ch.1".into()),
-            url: "https://x.example/foo/a".into(),
-        },
         SourceChapterRef {
             source_chapter_key: "b".into(),
             number: 3,
             title: Some("Ch.3".into()),
             url: "https://x.example/foo/b".into(),
         },
+        SourceChapterRef {
+            source_chapter_key: "a".into(),
+            number: 1,
+            title: Some("Ch.1".into()),
+            url: "https://x.example/foo/a".into(),
+        },
     ];
     crawler::sync_manga_chapters(&pool, "target", up.manga_id, &crawled)
         .await
@@ -1220,11 +1221,11 @@ async fn list_for_manga_places_null_source_index_last(pool: PgPool) {
     assert_eq!(
         titles,
         vec![
-            "Ch.3".to_string(),
             "Ch.1".to_string(),
             "User upload Ch.2".to_string(),
+            "Ch.3".to_string(),
         ],
-        "crawled rows ordered by reversed source_index; user upload \
+        "uploaded chapter (NULL source_index) interleaves by number between the \
-         (NULL source_index) falls through to the end",
+         crawled rows instead of falling to the end",
     );
 }

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.124.21",
+  "version": "0.124.22",
   "private": true,
   "type": "module",
   "scripts": {