Listing links point at the reader's page 1
(`.../uu/br_chapter-N/pg-1/`). The generic `derive_key_from_url` took
the last URL segment and returned `"pg-1"` for every chapter, so all
parsed chapters collapsed onto a single `chapter_sources` row downstream
and the first-manga chapter was the only row that survived. New
`derive_chapter_key_from_url` strips a trailing `/pg-\d+/` before
picking the chapter-identifying segment (`br_chapter-N` / `to_chapter-N`).
Notices, hiatus rows, and duplicate-numbered chapters are preserved as
distinct parser entries. The (manga_id, number) UNIQUE collapse in the
chapters table is a separate, follow-up concern handled in
feat/chapter-id-routing.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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