Defensive followup. If Deezer CDN ever refuses the upgraded
1900×1900 URL for a specific album (rare — empirically tested 4
albums and none hit it), pre-fix would have succeeded with the
1000×1000 URL and post-fix would have failed entirely.
Both download sites now retry with the original URL when the
upgraded URL fails:
- `core/metadata/artwork.py::download_cover_art` — auto post-process
flow. Resolves the original URL from album_info / context the same
way the existing path does.
- `core/tag_writer.py::download_cover_art` — captures the original
URL before upgrade so the retry has it without a second context
lookup.
Strictly non-regressive: worst plausible post-fix case is now
identical to pre-fix (cover at 1000×1000 succeeds). Fallback only
fires on the rare CDN-refusal edge.
Tests added (2):
- `test_tag_writer_retries_with_original_on_failure` — upgraded URL
raises, original succeeds, both attempts logged in call order
- `test_tag_writer_no_fallback_for_non_dzcdn_url` — non-Deezer URLs
go through unchanged, no fallback path triggered (single attempt)
Verification:
- 18/18 helper + integration tests pass
- 2561 full suite passes
- Ruff clean
8a4c0dc92a