fix(quick-19): multi-root path resolution for playlist M3U8 tracks

- Replace getLibraryRoot() with getAllLibraryRoots() returning all library paths
- Add resolveM3UPath() for multi-root resolution with knownPaths lookup
- Add toRelativePathMultiRoot() to save relative paths using correct root
- Update removeM3UEntries, replaceM3UEntryPaths, findM3UEntry for []string roots
- Update all 8 call sites in playlist.go for multi-root resolution
- Update existing test signatures for new []string parameter types
- Fix pre-existing golines formatting in scan_queue.go

backend/library/scan_queue.go

@@ -111,7 +111,9 @@ func (l *Library) SoftScanAllLibraries() error {
 	// dynamic library_id unsupported by sqlc. No user input.
 	for _, lib := range libs {
 		result, claimErr := l.db.ExecContext(
-			`UPDATE audio_files SET library_id = ? WHERE library_id = 0 AND file_path LIKE ? || '%'`,
+			`UPDATE audio_files SET library_id = ?`+
+				` WHERE library_id = 0`+
+				` AND file_path LIKE ? || '%'`,
 			lib.ID, lib.Path+"/",
 		)
 		if claimErr != nil {

backend/playlist/m3u.go

@@ -370,6 +370,65 @@ func toRelativePath(absolutePath, libraryRoot string) string {
 	return rel
 }
 
+// resolveM3UPath resolves a relative M3U path against multiple
+// library roots, returning the first absolute path that exists in
+// the knownPaths set. If the path is already absolute and known,
+// it is returned as-is. Falls back to the first root if no match
+// is found, preserving current behavior for phantom tracks.
+func resolveM3UPath(
+	relativePath string,
+	libraryRoots []string,
+	knownPaths map[string]struct{},
+) string {
+	if filepath.IsAbs(relativePath) {
+		if _, ok := knownPaths[relativePath]; ok {
+			return relativePath
+		}
+
+		return relativePath
+	}
+
+	for _, root := range libraryRoots {
+		absPath := filepath.Join(root, relativePath)
+		if _, ok := knownPaths[absPath]; ok {
+			return absPath
+		}
+	}
+
+	// Fallback: use first root (preserves current behavior
+	// for phantom tracks).
+	if len(libraryRoots) > 0 {
+		return filepath.Join(libraryRoots[0], relativePath)
+	}
+
+	return relativePath
+}
+
+// toRelativePathMultiRoot converts an absolute path to a relative
+// path using the first library root that contains the path.
+// If no root matches, the absolute path is returned unchanged.
+func toRelativePathMultiRoot(
+	absolutePath string,
+	libraryRoots []string,
+) string {
+	for _, root := range libraryRoots {
+		if root == "" {
+			continue
+		}
+
+		rel, err := filepath.Rel(root, absolutePath)
+		if err != nil {
+			continue
+		}
+
+		if !strings.HasPrefix(rel, "..") {
+			return rel
+		}
+	}
+
+	return absolutePath
+}
+
 // isValidM3UExtension checks whether a file extension is a
 // recognized M3U variant.
 func isValidM3UExtension(ext string) bool {
@@ -414,17 +473,18 @@ func extractPlaylistID(filePath string) int64 {
 }
 
 // removeM3UEntries removes entries from a slice whose resolved
-// absolute paths appear in the target set.
+// absolute paths appear in the target set. Each entry is resolved
+// against all library roots.
 func removeM3UEntries(
 	entries []m3uEntry,
 	targetAbsPaths map[string]struct{},
-	libraryRoot string,
+	libraryRoots []string,
 ) []m3uEntry {
 	result := make([]m3uEntry, 0, len(entries))
 
 	for _, e := range entries {
-		absPath := toAbsolutePath(
-			e.RelativePath, libraryRoot,
+		absPath := resolveM3UPath(
+			e.RelativePath, libraryRoots, targetAbsPaths,
 		)
 		if _, remove := targetAbsPaths[absPath]; remove {
 			continue
@@ -438,19 +498,26 @@ func removeM3UEntries(
 
 // replaceM3UEntryPaths replaces the relative paths of entries
 // whose resolved absolute paths match keys in the replacements
-// map. Values are new relative paths.
+// map. Values are new relative paths. Each entry is resolved
+// against all library roots.
 func replaceM3UEntryPaths(
 	entries []m3uEntry,
 	replacements map[string]string,
-	libraryRoot string,
+	libraryRoots []string,
 ) []m3uEntry {
+	// Build a set of replacement keys for resolveM3UPath lookup.
+	keySet := make(map[string]struct{}, len(replacements))
+	for k := range replacements {
+		keySet[k] = struct{}{}
+	}
+
 	result := make([]m3uEntry, len(entries))
 
 	for i, e := range entries {
 		result[i] = e
 
-		absPath := toAbsolutePath(
-			e.RelativePath, libraryRoot,
+		absPath := resolveM3UPath(
+			e.RelativePath, libraryRoots, keySet,
 		)
 
 		if newRel, ok := replacements[absPath]; ok {
@@ -462,16 +529,21 @@ func replaceM3UEntryPaths(
 }
 
 // findM3UEntry finds the M3U entry whose resolved absolute path
-// matches the given target path. Returns the entry and its index,
-// or -1 if not found.
+// matches the given target path. Each entry is resolved against
+// all library roots. Returns the entry and its index, or -1 if
+// not found.
 func findM3UEntry(
 	entries []m3uEntry,
 	targetAbsPath string,
-	libraryRoot string,
+	libraryRoots []string,
 ) (m3uEntry, int) {
+	targetSet := map[string]struct{}{
+		targetAbsPath: {},
+	}
+
 	for i, e := range entries {
-		absPath := toAbsolutePath(
-			e.RelativePath, libraryRoot,
+		absPath := resolveM3UPath(
+			e.RelativePath, libraryRoots, targetSet,
 		)
 		if absPath == targetAbsPath {
 			return e, i

backend/playlist/m3u_test.go

@@ -731,7 +731,9 @@ func TestRemoveM3UEntries(t *testing.T) {
 		"/music/Artist/Song2.flac": {},
 	}
 
-	result := removeM3UEntries(entries, targets, "/music")
+	result := removeM3UEntries(
+		entries, targets, []string{"/music"},
+	)
 
 	if len(result) != 2 {
 		t.Fatalf("expected 2 entries, got %d", len(result))
@@ -765,7 +767,9 @@ func TestRemoveM3UEntriesAll(t *testing.T) {
 		"/music/Song.flac": {},
 	}
 
-	result := removeM3UEntries(entries, targets, "/music")
+	result := removeM3UEntries(
+		entries, targets, []string{"/music"},
+	)
 
 	if len(result) != 0 {
 		t.Errorf("expected 0 entries, got %d", len(result))
@@ -793,7 +797,7 @@ func TestReplaceM3UEntryPaths(t *testing.T) {
 	}
 
 	result := replaceM3UEntryPaths(
-		entries, replacements, "/music",
+		entries, replacements, []string{"/music"},
 	)
 
 	if len(result) != 2 {
@@ -836,7 +840,8 @@ func TestFindM3UEntry(t *testing.T) {
 	}
 
 	entry, idx := findM3UEntry(
-		entries, "/music/Artist/Song2.flac", "/music",
+		entries, "/music/Artist/Song2.flac",
+		[]string{"/music"},
 	)
 
 	if idx != 1 {
@@ -853,7 +858,8 @@ func TestFindM3UEntry(t *testing.T) {
 
 	// Not found.
 	_, idx = findM3UEntry(
-		entries, "/music/Artist/Missing.flac", "/music",
+		entries, "/music/Artist/Missing.flac",
+		[]string{"/music"},
 	)
 
 	if idx != -1 {

backend/playlist/playlist.go

@@ -367,12 +367,21 @@ func (s *Service) mergeTracksForPlaylist(
 		return dbTracksToSlice(dbTracks)
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
+
+	// Build a set of known DB paths for multi-root resolution.
+	knownPaths := make(
+		map[string]struct{}, len(dbTracks),
+	)
+	for k := range dbTracks {
+		knownPaths[k] = struct{}{}
+	}
+
 	tracks := make([]Track, 0, len(parsed.Entries))
 
 	for i, entry := range parsed.Entries {
-		absPath := toAbsolutePath(
-			entry.RelativePath, libraryRoot,
+		absPath := resolveM3UPath(
+			entry.RelativePath, libraryRoots, knownPaths,
 		)
 
 		if dbTrack, ok := dbTracks[absPath]; ok {
@@ -841,7 +850,7 @@ func (s *Service) ImportPlaylist(
 		)
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 
 	var (
 		resolved   int
@@ -850,14 +859,37 @@ func (s *Service) ImportPlaylist(
 	)
 
 	for _, entry := range parsed.Entries {
-		absPath := toAbsolutePath(
-			entry.RelativePath, libraryRoot,
-		)
+		var audioFile sqlcgen.AudioFile
 
-		audioFile, lookupErr := s.db.Queries.GetAudioFileByPath(
-			s.db.Ctx, absPath,
-		)
-		if lookupErr != nil {
+		found := false
+
+		if filepath.IsAbs(entry.RelativePath) {
+			af, err := s.db.Queries.GetAudioFileByPath(
+				s.db.Ctx, entry.RelativePath,
+			)
+			if err == nil {
+				audioFile = af
+				found = true
+			}
+		} else {
+			for _, root := range libraryRoots {
+				absPath := toAbsolutePath(
+					entry.RelativePath, root,
+				)
+
+				af, err := s.db.Queries.GetAudioFileByPath(
+					s.db.Ctx, absPath,
+				)
+				if err == nil {
+					audioFile = af
+					found = true
+
+					break
+				}
+			}
+		}
+
+		if !found {
 			// Track not in library — will appear as phantom.
 			unresolved++
 
@@ -876,7 +908,7 @@ func (s *Service) ImportPlaylist(
 			s.logger.Warn(
 				"Could not add imported track",
 				"playlistId", created.ID,
-				"path", absPath,
+				"path", audioFile.FilePath,
 				"err", addErr,
 			)
 
@@ -890,7 +922,7 @@ func (s *Service) ImportPlaylist(
 	// Save the M3U8 file with entries (preserves unresolved
 	// paths for phantom display).
 	s.saveImportedPlaylistFile(
-		created.ID, playlistName, parsed.Entries, libraryRoot,
+		created.ID, playlistName, parsed.Entries, libraryRoots,
 	)
 
 	s.logger.Info(
@@ -981,7 +1013,7 @@ func (s *Service) RestoreAllPlaylists() {
 		return
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 
 	var totalRestored, totalUnresolved int
 
@@ -997,7 +1029,7 @@ func (s *Service) RestoreAllPlaylists() {
 		}
 
 		restored, unresolved := s.restoreSinglePlaylist(
-			playlistID, file, libraryRoot,
+			playlistID, file, libraryRoots,
 		)
 
 		totalRestored += restored
@@ -1014,11 +1046,12 @@ func (s *Service) RestoreAllPlaylists() {
 }
 
 // restoreSinglePlaylist restores tracks for a single playlist
-// from its M3U8 file.
+// from its M3U8 file. Each M3U8 entry is resolved against all
+// library roots.
 func (s *Service) restoreSinglePlaylist(
 	playlistID int64,
 	m3uPath string,
-	libraryRoot string,
+	libraryRoots []string,
 ) (restored, unresolved int) {
 	parsed, err := parseM3U8(m3uPath)
 	if err != nil {
@@ -1049,14 +1082,37 @@ func (s *Service) restoreSinglePlaylist(
 	var position int
 
 	for _, entry := range parsed.Entries {
-		absPath := toAbsolutePath(
-			entry.RelativePath, libraryRoot,
-		)
+		var audioFile sqlcgen.AudioFile
 
-		audioFile, lookupErr := s.db.Queries.GetAudioFileByPath(
-			s.db.Ctx, absPath,
-		)
-		if lookupErr != nil {
+		found := false
+
+		if filepath.IsAbs(entry.RelativePath) {
+			af, lookupErr := s.db.Queries.GetAudioFileByPath(
+				s.db.Ctx, entry.RelativePath,
+			)
+			if lookupErr == nil {
+				audioFile = af
+				found = true
+			}
+		} else {
+			for _, root := range libraryRoots {
+				absPath := toAbsolutePath(
+					entry.RelativePath, root,
+				)
+
+				af, lookupErr := s.db.Queries.GetAudioFileByPath(
+					s.db.Ctx, absPath,
+				)
+				if lookupErr == nil {
+					audioFile = af
+					found = true
+
+					break
+				}
+			}
+		}
+
+		if !found {
 			unresolved++
 
 			continue
@@ -1074,7 +1130,7 @@ func (s *Service) restoreSinglePlaylist(
 			s.logger.Warn(
 				"Could not restore track",
 				"playlistId", playlistID,
-				"path", absPath,
+				"path", audioFile.FilePath,
 				"err", addErr,
 			)
 
@@ -1169,24 +1225,29 @@ func (s *Service) playlistsDir() (string, error) {
 	return dir, nil
 }
 
-// getLibraryRoot returns the library root directory path.
-// It first checks the legacy config DirectoryPath; if that is
-// empty (removed during multi-library migration) it falls back
-// to the first library's path from the database.
-func (s *Service) getLibraryRoot() string {
+// getAllLibraryRoots returns the root directory paths of all
+// configured libraries. It first checks the legacy config
+// DirectoryPath; if that is set, it returns a single-element
+// slice. Otherwise it queries all libraries from the database.
+func (s *Service) getAllLibraryRoots() []string {
+	// Legacy config fallback.
 	if s.libraryDir != nil {
 		if dir := s.libraryDir.GetLibraryDirectory(); dir != "" {
-			return dir
+			return []string{dir}
 		}
 	}
 
-	// Fallback: query the first library from the database.
 	libs, err := s.db.Queries.GetAllLibraries(s.db.Ctx)
 	if err != nil || len(libs) == 0 {
-		return ""
+		return nil
 	}
 
-	return libs[0].Path
+	roots := make([]string, len(libs))
+	for i, lib := range libs {
+		roots[i] = lib.Path
+	}
+
+	return roots
 }
 
 // savePlaylistFile saves the current state of a playlist to its
@@ -1243,7 +1304,7 @@ func (s *Service) saveImportedPlaylistFile(
 	playlistID int64,
 	name string,
 	entries []m3uEntry,
-	libraryRoot string,
+	libraryRoots []string,
 ) {
 	dir, err := s.playlistsDir()
 	if err != nil {
@@ -1255,16 +1316,22 @@ func (s *Service) saveImportedPlaylistFile(
 		return
 	}
 
-	// Convert any absolute paths in entries to relative.
+	// Convert any absolute paths in entries to relative
+	// using the correct library root for each track.
 	converted := make([]m3uEntry, len(entries))
 
 	for i, entry := range entries {
+		// Resolve against all roots to get the absolute path,
+		// then convert back to relative using the matching root.
+		absPath := resolveM3UPath(
+			entry.RelativePath,
+			libraryRoots,
+			nil,
+		)
+
 		converted[i] = m3uEntry{
-			RelativePath: toRelativePath(
-				toAbsolutePath(
-					entry.RelativePath, libraryRoot,
-				),
-				libraryRoot,
+			RelativePath: toRelativePathMultiRoot(
+				absPath, libraryRoots,
 			),
 			DurationSec:  entry.DurationSec,
 			DisplayTitle: entry.DisplayTitle,
@@ -1301,7 +1368,7 @@ func (s *Service) buildM3UEntries(
 		return nil
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 	entries := make([]m3uEntry, 0, len(rows))
 
 	for _, row := range rows {
@@ -1310,8 +1377,8 @@ func (s *Service) buildM3UEntries(
 		)
 
 		entries = append(entries, m3uEntry{
-			RelativePath: toRelativePath(
-				row.FilePath, libraryRoot,
+			RelativePath: toRelativePathMultiRoot(
+				row.FilePath, libraryRoots,
 			),
 			DurationSec: durationSec,
 			DisplayTitle: displayTitle(
@@ -1445,7 +1512,7 @@ func (s *Service) FindPhantomMatches(
 		)
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 
 	// Load M3U8 entries for display title / duration data.
 	m3uPath, err := findPlaylistFile(dir, playlistID)
@@ -1465,11 +1532,13 @@ func (s *Service) FindPhantomMatches(
 	}
 
 	// Build a lookup from absolute path to M3U entry.
+	// Use resolveM3UPath with a nil knownPaths to get the
+	// first-root fallback for each entry.
 	entryByPath := make(map[string]m3uEntry, len(entries))
 
 	for _, e := range entries {
-		absPath := toAbsolutePath(
-			e.RelativePath, libraryRoot,
+		absPath := resolveM3UPath(
+			e.RelativePath, libraryRoots, nil,
 		)
 		entryByPath[absPath] = e
 	}
@@ -1533,7 +1602,7 @@ func (s *Service) GetPhantomCandidates(
 		)
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 
 	// Find the M3U entry for this phantom.
 	m3uPath, err := findPlaylistFile(dir, playlistID)
@@ -1549,7 +1618,7 @@ func (s *Service) GetPhantomCandidates(
 		parsed, parseErr := parseM3U8(m3uPath)
 		if parseErr == nil {
 			entry, _ = findM3UEntry(
-				parsed.Entries, phantomPath, libraryRoot,
+				parsed.Entries, phantomPath, libraryRoots,
 			)
 		}
 	}
@@ -1613,7 +1682,7 @@ func (s *Service) ResolvePhantomTracks(
 		)
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 
 	m3uPath, err := findPlaylistFile(dir, playlistID)
 	if err != nil || m3uPath == "" {
@@ -1681,7 +1750,9 @@ func (s *Service) ResolvePhantomTracks(
 			continue
 		}
 
-		newRel := toRelativePath(resolvedAbs, libraryRoot)
+		newRel := toRelativePathMultiRoot(
+			resolvedAbs, libraryRoots,
+		)
 		pathReplacements[phantomAbs] = newRel
 		resolved++
 	}
@@ -1689,7 +1760,7 @@ func (s *Service) ResolvePhantomTracks(
 	// Rewrite the M3U8 with updated paths.
 	if resolved > 0 {
 		updated := replaceM3UEntryPaths(
-			parsed.Entries, pathReplacements, libraryRoot,
+			parsed.Entries, pathReplacements, libraryRoots,
 		)
 
 		playlist, nameErr := s.db.Queries.GetPlaylist(
@@ -1740,7 +1811,7 @@ func (s *Service) RemovePhantomTracks(
 		)
 	}
 
-	libraryRoot := s.getLibraryRoot()
+	libraryRoots := s.getAllLibraryRoots()
 
 	m3uPath, err := findPlaylistFile(dir, playlistID)
 	if err != nil || m3uPath == "" {
@@ -1766,7 +1837,7 @@ func (s *Service) RemovePhantomTracks(
 	}
 
 	updated := removeM3UEntries(
-		parsed.Entries, targetSet, libraryRoot,
+		parsed.Entries, targetSet, libraryRoots,
 	)
 
 	playlist, err := s.db.Queries.GetPlaylist(