Artist detail pages ran check_album_exists_with_editions and check_track_exists
per discography item, each firing 5+ title variations times 3 artist variations
of fuzzy LIKE searches plus fallback broad-artist queries. For a 30-album artist
that was ~450 SQL round-trips just to answer "which of these do I own."
Hoist the artist's library albums and tracks into memory once per request via
two new helpers — get_candidate_albums_for_artist and get_candidate_tracks_for_albums —
and thread them through as optional candidate_albums / candidate_tracks params on
check_album_exists_with_editions, check_album_exists_with_completeness,
check_track_exists, check_album_completion, and check_single_completion.
Batched path scores the same _calculate_album_confidence / _calculate_track_confidence
against the in-memory list, preserving Smart Edition Matching and accuracy.
Title-only cross-artist fallback still fires for collaborative-album edge cases.
None on either param preserves legacy per-item SQL behavior for unaffected callers.
Applied to both /api/library/completion-stream (library artist detail page) and
iter_artist_discography_completion_events (Artists search page). Timing logs
added to confirm the pre-fetch cost and loop elapsed time.
On a Kendrick page load, per-album resolution drops from ~8 seconds to under
the 50ms streaming sleep floor. Observed ~100x SQL reduction on the happy path.
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