fix(opds): handle dead sources and prevent kosync binary hash crashes (#2116)

server/src/main/kotlin/suwayomi/tachidesk/opds/impl/OpdsFeedBuilder.kt

@@ -644,6 +644,16 @@ object OpdsFeedBuilder {
                 skipMetadata,
             )
 
+        // Return a not-found feed if all available chapters are filtered out as unreachable
+        if (skipMetadata && chapterEntries.isEmpty() && totalChapters > 0L) {
+            return buildNotFoundFeed(
+                baseUrl = baseUrl,
+                locale = locale,
+                idPath = "series/$mangaId/chapters",
+                title = MR.strings.opds_error_chapters_not_found.localized(locale, pageNum),
+            )
+        }
+
         // If no chapters are found in the database, attempt to fetch them from the source.
         if (chapterEntries.isEmpty() && totalChapters == 0L) {
             try {

server/src/main/kotlin/suwayomi/tachidesk/opds/repository/ChapterRepository.kt

@@ -169,6 +169,8 @@ object ChapterRepository {
                     }
                 }
             }.awaitAll()
+                // Exclude unreachable chapters that are not downloaded and have no page count
+                .filter { it.downloaded || it.pageCount > 0 }
 
         return Pair(enrichedChapters, totalCount)
     }