Adds an opt-in `rank_candidates_by_quality` profile flag. When on, the
priority-mode download walk orders candidates by the ranked-target quality
(confidence/speed only break ties) instead of confidence-first. Default off
keeps the byte-for-byte old behaviour, so existing installs are unaffected.
Best-quality search mode is always quality-first regardless of the flag; the
toggle only affects priority mode. Search-time source selection is unchanged —
nothing is skipped, so a track can never go missing, only the order in which
copies are tried changes.
The version-mismatch force-import follows automatically: it accepts the
first-tried (= best-ordered) quarantined candidate, which is the highest-quality
one once the walk is quality-first. No change to its selection logic needed.
- core/quality/selection.py: load_rank_candidates_by_quality() (fail-closed).
- core/downloads/task_worker.py: _best_quality_ordering -> _candidate_ordering;
quality-first when best_quality mode OR the toggle is on.
- database/music_database.py: default profile carries the flag (False).
- web_server.py: flag is preserved globally across preset apply/reset, like
search_mode.
- core/imports/version_mismatch_fallback.py: comment clarified (no behaviour
change).
Tests (TDD): load_rank_candidates_by_quality default/enabled/disabled/error;
_candidate_ordering across all mode+toggle combinations + fail-closed.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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