feat: autotag mixed-bag splitting, search relevance fixes, and multi-library download imports

Autotag: detect "junk drawer" folders with no artist/album consensus
and split them into synthetic per-cluster groups instead of forcing
one match on an unrelated pile of tracks; repair tagging_items rows
left behind by a prior scan orphan-cleanup gap.

Explore: fix an exact artist-name search being drowned out by its own
catalog entries in intent-prior scoring, and prune stale in_library
bookkeeping left behind when a referenced library row is deleted.

Download: fix a multi-library regression where every import failed
with "no library root configured" — the importer resolved the
library root from a legacy single-library config field that nothing
populates in the current multi-library model. It now resolves the
destination library per-request from the request's own library_id.
Also widen the Soulseek search window (12s -> 20s), measured against
real request history to be missing available peers on live queries.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y2Agd9af5hE7qzti2ackiS

backend/database/sql/queries/artist_credit.sql

@@ -32,3 +32,11 @@ SELECT
   (SELECT COUNT(*) FROM recordings WHERE artist_credit_id = ?1) +
   (SELECT COUNT(*) FROM release_groups WHERE album_artist_credit_id = ?1)
 AS total;
+
+-- name: GetOrphanedArtistCreditIDs :many
+-- Artist credits no longer used by any recording or release group - run
+-- after orphaned recordings/release groups are deleted, so a credit
+-- that only existed for now-removed tracks is cleaned up too.
+SELECT ac.id FROM artist_credit ac
+WHERE NOT EXISTS (SELECT 1 FROM recordings r WHERE r.artist_credit_id = ac.id)
+  AND NOT EXISTS (SELECT 1 FROM release_groups rg WHERE rg.album_artist_credit_id = ac.id);

backend/database/sql/queries/artist_credit_artists.sql

@@ -18,3 +18,7 @@ WHERE id =?;
 -- name: DeleteAllArtistCreditArtists :exec
 DELETE FROM artist_credit_artist;
 
+-- name: DeleteArtistCreditArtistByCredit :exec
+DELETE FROM artist_credit_artist
+WHERE credit_id = ?;
+

backend/database/sql/queries/artists.sql

@@ -39,6 +39,15 @@ JOIN artist_credit ac ON ac.id = aca.credit_id
 JOIN release_groups rg ON rg.album_artist_credit_id = ac.id
 ORDER BY a.name;
 
+-- name: GetOrphanedArtistIDs :many
+-- Artists no longer credited on any recording or release group - left
+-- behind when a scan's orphan cleanup removes the audio_files that used
+-- to justify them, since deleting an audio_files row doesn't cascade.
+SELECT a.id FROM artists a
+WHERE NOT EXISTS (
+    SELECT 1 FROM artist_credit_artist aca WHERE aca.artist_id = a.id
+);
+
 -- name: GetAlbumArtistsByLibrary :many
 SELECT DISTINCT a.id, a.name, a.mbid
 FROM artists a

backend/database/sql/queries/recordings.sql

@@ -37,3 +37,11 @@ ORDER BY name;
 
 -- name: CountRecordingsByArtistCredit :one
 SELECT COUNT(*) FROM recordings WHERE artist_credit_id = ?;
+
+-- name: GetOrphanedRecordingIDs :many
+-- Recordings no longer backed by any audio_files row - left behind
+-- when a scan's orphan cleanup deletes the file that used to own them,
+-- since deleting audio_files doesn't cascade to recordings.
+SELECT r.id FROM recordings r
+LEFT JOIN audio_files af ON af.recording_id = r.id
+WHERE af.id IS NULL;

backend/database/sql/queries/release_group_recordings.sql

@@ -26,3 +26,7 @@ WHERE release_group_id = ? AND recording_id = ?;
 
 -- name: DeleteAllReleaseGroupRecordings :exec
 DELETE FROM release_group_recordings;
+
+-- name: DeleteReleaseGroupRecordingsByRecording :exec
+DELETE FROM release_group_recordings
+WHERE recording_id = ?;

backend/database/sql/queries/release_groups.sql

@@ -167,6 +167,14 @@ ORDER BY rg.name;
 -- name: CountReleaseGroupRecordings :one
 SELECT COUNT(*) FROM release_group_recordings WHERE release_group_id = ?;
 
+-- name: GetOrphanedReleaseGroupIDs :many
+-- Release groups with no recordings left in them - run after orphaned
+-- recordings (and their release_group_recordings rows) are deleted, so
+-- a release group whose last owned track was removed is cleaned up too.
+SELECT rg.id FROM release_groups rg
+LEFT JOIN release_group_recordings rgr ON rgr.release_group_id = rg.id
+WHERE rgr.id IS NULL;
+
 -- name: GetAlbumsByArtistByLibrary :many
 SELECT
     rg.id,

backend/database/sql/queries/tagging_items.sql

@@ -24,11 +24,63 @@ WHERE group_key = ?;
 DELETE FROM tagging_items
 WHERE group_key = ? AND track_count <= 0;
 
+-- name: PruneOrphanedTaggingItems :exec
+-- Self-healing sweep for rows whose track_count bookkeeping (scan
+-- orphan cleanup, maybeRebindTaggingGroup, SplitMixedFolder) never
+-- ran or drifted: a cancelled scan, a library move/rename the
+-- SoftScanAllLibraries disk-count/mtime heuristic did not catch, or
+-- a decrement that landed without its paired delete. Rather than
+-- trust track_count, this checks the ground truth directly: any
+-- group_key no audio_files row still points at is gone, and its
+-- tagging_items row (and cascaded tagging_candidates) should be too.
+-- Cheap: one indexed (idx_audio_files_group_key) existence check per
+-- row. Called opportunistically wherever the pending list is read,
+-- so stale entries cannot linger indefinitely between full rescans.
+DELETE FROM tagging_items
+WHERE NOT EXISTS (
+  SELECT 1 FROM audio_files af WHERE af.group_key = tagging_items.group_key
+);
+
+-- name: MarkTaggingItemSynthetic :exec
+-- Stamps a group as carved out of parent_group_key by
+-- SplitMixedFolder.  Idempotent: safe to call every time a track
+-- is migrated into the synthetic group, not just on first creation.
+UPDATE tagging_items
+SET synthetic = 1,
+    parent_group_key = ?
+WHERE group_key = ?;
+
 -- name: GetTaggingItem :one
 SELECT * FROM tagging_items
 WHERE group_key = ?
 LIMIT 1;
 
+-- name: ListLikelyMixedBagGroupKeys :many
+-- Cheap, whole-library triage pass for autotag.IsMixedBag: one
+-- grouped scan over audio_files (indexed on group_key) rather than
+-- hydrating every group's full track list in Go.  LOWER/TRIM is an
+-- approximation of autotag.Normalize (no unicode fold, no qualifier
+-- stripping) so this can flag a false positive Normalize would
+-- clear, or miss a true one Normalize would catch.  Treat it as a
+-- triage filter for which groups are worth a real autotag.
+-- IsMixedBag check, or a badge at minimum, not the final word.
+SELECT ti.group_key
+FROM tagging_items ti
+JOIN audio_files af ON af.group_key = ti.group_key
+LEFT JOIN recordings r ON af.recording_id = r.id
+LEFT JOIN artist_credit ac ON r.artist_credit_id = ac.id
+LEFT JOIN release_group_recordings rgr ON rgr.recording_id = r.id
+LEFT JOIN release_groups rg ON rg.id = rgr.release_group_id
+WHERE ti.synthetic = 0
+  AND ti.track_count >= 4
+  AND (
+    ti.album_artist = ''
+    OR LOWER(TRIM(ti.album_artist)) IN ('various artists', 'various', 'va', 'v.a.', 'v a', 'unknown')
+  )
+GROUP BY ti.group_key
+HAVING COUNT(DISTINCT CASE WHEN ac.text != '' THEN LOWER(TRIM(ac.text)) END) > 1
+   AND COUNT(DISTINCT CASE WHEN rg.name != '' THEN LOWER(TRIM(rg.name)) END) > 1;
+
 -- name: CountPendingTaggingItems :one
 SELECT COUNT(*) FROM tagging_items
 WHERE status = 'pending'
@@ -71,7 +123,8 @@ SELECT
   ti.score,
   ti.last_checked_at,
   ti.status,
-  ti.created_at
+  ti.created_at,
+  ti.synthetic
 FROM tagging_items ti
 LEFT JOIN libraries lb ON lb.id = ti.library_id
 WHERE (CAST(@library_id AS INTEGER) = 0 OR ti.library_id = @library_id)
@@ -102,7 +155,8 @@ SELECT
   ti.score,
   ti.last_checked_at,
   ti.status,
-  ti.created_at
+  ti.created_at,
+  ti.synthetic
 FROM tagging_items ti
 LEFT JOIN libraries lb ON lb.id = ti.library_id
 WHERE ti.group_key = ?
@@ -130,6 +184,10 @@ ORDER BY ti.created_at DESC, ti.group_key
 LIMIT @row_limit OFFSET @row_offset;
 
 -- name: ListAudioFilesInTaggingGroup :many
+-- album_name/album_artist are the PER-TRACK tags (via each track's
+-- own release_group link), not the folder-level tagging_items
+-- values.  SplitMixedFolder clusters on these to find sub-albums
+-- hiding inside a folder full of unrelated tracks.
 SELECT
   af.id,
   af.file_path,
@@ -140,10 +198,15 @@ SELECT
   COALESCE(r.disc_number, 0) AS disc_number,
   COALESCE(r.name, '') AS title,
   COALESCE(ac.text, '') AS artist_name,
-  COALESCE(r.mbid, '') AS recording_mbid
+  COALESCE(r.mbid, '') AS recording_mbid,
+  COALESCE(rg.name, '') AS album_name,
+  COALESCE(rgac.text, '') AS album_artist
 FROM audio_files af
 LEFT JOIN recordings r ON af.recording_id = r.id
 LEFT JOIN artist_credit ac ON r.artist_credit_id = ac.id
+LEFT JOIN release_group_recordings rgr ON rgr.recording_id = r.id
+LEFT JOIN release_groups rg ON rg.id = rgr.release_group_id
+LEFT JOIN artist_credit rgac ON rg.album_artist_credit_id = rgac.id
 WHERE af.group_key = ?
 ORDER BY COALESCE(r.disc_number, 0),
          COALESCE(r.track_number, 0),