diff --git a/analysis_options.yaml b/analysis_options.yaml
index 577a9667..e188dd4f 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -36,7 +36,11 @@ linter:
   rules:
     # avoid_print: false  # Uncomment to disable the `avoid_print` rule
     # prefer_single_quotes: true  # Uncomment to enable the `prefer_single_quotes` rule
+    always_declare_return_types: true
     avoid_dynamic_calls: true
+    avoid_types_as_parameter_names: true
+    strict_top_level_inference: true
+    type_annotate_public_apis: true
     cancel_subscriptions: true
     close_sinks: true
 
diff --git a/go_backend/coverage_test_helpers_test.go b/go_backend/coverage_test_helpers_test.go
index 16aefc48..822faec1 100644
--- a/go_backend/coverage_test_helpers_test.go
+++ b/go_backend/coverage_test_helpers_test.go
@@ -399,13 +399,3 @@ func createTestExtensionPackage(t *testing.T, path, name, version, js string, ex
 		}
 	}
 }
-
-func buildRawAPEItem(key, value string, flags uint32) []byte {
-	var buf bytes.Buffer
-	_ = binary.Write(&buf, binary.LittleEndian, uint32(len(value)))
-	_ = binary.Write(&buf, binary.LittleEndian, flags)
-	buf.WriteString(key)
-	buf.WriteByte(0)
-	buf.WriteString(value)
-	return buf.Bytes()
-}
diff --git a/go_backend/exports.go b/go_backend/exports.go
index fcc22361..97416180 100644
--- a/go_backend/exports.go
+++ b/go_backend/exports.go
@@ -2230,7 +2230,7 @@ func ConvertSpotifyToDeezer(resourceType, spotifyID string) (string, error) {
 		return string(jsonBytes), nil
 	}
 
-	return "", fmt.Errorf("Spotify to Deezer conversion only supported for tracks and albums. Please search by name for %s", resourceType)
+	return "", fmt.Errorf("spotify to Deezer conversion only supported for tracks and albums: please search by name for %s", resourceType)
 }
 
 func CheckAvailabilityFromDeezerID(deezerTrackID string) (string, error) {
diff --git a/go_backend/extension_manager.go b/go_backend/extension_manager.go
index 07b70dba..80649d09 100644
--- a/go_backend/extension_manager.go
+++ b/go_backend/extension_manager.go
@@ -157,12 +157,12 @@ func (m *extensionManager) SetDirectories(extensionsDir, dataDir string) error {
 
 func (m *extensionManager) LoadExtensionFromFile(filePath string) (*loadedExtension, error) {
 	if !strings.HasSuffix(strings.ToLower(filePath), ".spotiflac-ext") {
-		return nil, fmt.Errorf("Invalid file format. Please select a .spotiflac-ext file")
+		return nil, fmt.Errorf("invalid file format: please select a .spotiflac-ext file")
 	}
 
 	zipReader, err := zip.OpenReader(filePath)
 	if err != nil {
-		return nil, fmt.Errorf("Cannot open extension file. The file may be corrupted or not a valid extension package")
+		return nil, fmt.Errorf("cannot open extension file: the file may be corrupted or not a valid extension package")
 	}
 	defer zipReader.Close()
 
@@ -187,16 +187,16 @@ func (m *extensionManager) LoadExtensionFromFile(filePath string) (*loadedExtens
 	}
 
 	if manifestData == nil {
-		return nil, fmt.Errorf("Invalid extension package: manifest.json not found")
+		return nil, fmt.Errorf("invalid extension package: manifest.json not found")
 	}
 
 	if !hasIndexJS {
-		return nil, fmt.Errorf("Invalid extension package: index.js not found")
+		return nil, fmt.Errorf("invalid extension package: index.js not found")
 	}
 
 	manifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid extension manifest: %w", err)
+		return nil, fmt.Errorf("invalid extension manifest: %w", err)
 	}
 
 	m.mu.RLock()
@@ -214,9 +214,9 @@ func (m *extensionManager) LoadExtensionFromFile(filePath string) (*loadedExtens
 		if versionCompare > 0 {
 			return m.UpgradeExtension(filePath)
 		} else if versionCompare == 0 {
-			return nil, fmt.Errorf("Extension '%s' v%s is already installed", existingDisplayName, existingVersion)
+			return nil, fmt.Errorf("extension '%s' v%s is already installed", existingDisplayName, existingVersion)
 		} else {
-			return nil, fmt.Errorf("Cannot downgrade '%s' from v%s to v%s", existingDisplayName, existingVersion, manifest.Version)
+			return nil, fmt.Errorf("cannot downgrade '%s' from v%s to v%s", existingDisplayName, existingVersion, manifest.Version)
 		}
 	}
 
@@ -224,7 +224,7 @@ func (m *extensionManager) LoadExtensionFromFile(filePath string) (*loadedExtens
 	defer m.mu.Unlock()
 
 	if _, exists := m.extensions[manifest.Name]; exists {
-		return nil, fmt.Errorf("Extension '%s' was installed by another process", manifest.DisplayName)
+		return nil, fmt.Errorf("extension '%s' was installed by another process", manifest.DisplayName)
 	}
 
 	extDir := filepath.Join(m.extensionsDir, manifest.Name)
@@ -426,7 +426,7 @@ func initializeExtensionRuntimeWithSettings(
 ) error {
 	settingsJSON, err := json.Marshal(settings)
 	if err != nil {
-		return fmt.Errorf("Failed to save settings")
+		return fmt.Errorf("failed to save settings")
 	}
 
 	script := fmt.Sprintf(`
@@ -472,7 +472,7 @@ func initializeExtensionWithSettingsLocked(
 	settings map[string]interface{},
 ) error {
 	if ext.VM == nil {
-		return fmt.Errorf("Extension failed to load. Please reinstall the extension")
+		return fmt.Errorf("extension failed to load: please reinstall the extension")
 	}
 
 	if err := initializeExtensionRuntimeWithSettings(ext.VM, ext.ID, settings); err != nil {
@@ -570,7 +570,7 @@ func (m *extensionManager) UnloadExtension(extensionID string) error {
 
 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}
 
 	ext.VMMu.Lock()
@@ -589,7 +589,7 @@ func (m *extensionManager) GetExtension(extensionID string) (*loadedExtension, e
 
 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return nil, fmt.Errorf("Extension not found")
+		return nil, fmt.Errorf("extension not found")
 	}
 	return ext, nil
 }
@@ -611,7 +611,7 @@ func (m *extensionManager) SetExtensionEnabled(extensionID string, enabled bool)
 
 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}
 
 	if enabled {
@@ -689,12 +689,12 @@ func (m *extensionManager) loadExtensionFromDirectory(dirPath string) (*loadedEx
 
 	manifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid extension manifest: %w", err)
+		return nil, fmt.Errorf("invalid extension manifest: %w", err)
 	}
 
 	indexPath := filepath.Join(dirPath, "index.js")
 	if _, err := os.Stat(indexPath); os.IsNotExist(err) {
-		return nil, fmt.Errorf("Extension is missing index.js file")
+		return nil, fmt.Errorf("extension is missing index.js file")
 	}
 
 	if existing, exists := m.extensions[manifest.Name]; exists {
@@ -757,12 +757,12 @@ func (m *extensionManager) RemoveExtension(extensionID string) error {
 // Only allows upgrades (new version > current version), not downgrades
 func (m *extensionManager) UpgradeExtension(filePath string) (*loadedExtension, error) {
 	if !strings.HasSuffix(strings.ToLower(filePath), ".spotiflac-ext") {
-		return nil, fmt.Errorf("Invalid file format. Please select a .spotiflac-ext file")
+		return nil, fmt.Errorf("invalid file format: please select a .spotiflac-ext file")
 	}
 
 	zipReader, err := zip.OpenReader(filePath)
 	if err != nil {
-		return nil, fmt.Errorf("Cannot open extension file. The file may be corrupted or not a valid extension package")
+		return nil, fmt.Errorf("cannot open extension file: the file may be corrupted or not a valid extension package")
 	}
 	defer zipReader.Close()
 
@@ -787,16 +787,16 @@ func (m *extensionManager) UpgradeExtension(filePath string) (*loadedExtension,
 	}
 
 	if manifestData == nil {
-		return nil, fmt.Errorf("Invalid extension package: manifest.json not found")
+		return nil, fmt.Errorf("invalid extension package: manifest.json not found")
 	}
 
 	if !hasIndexJS {
-		return nil, fmt.Errorf("Invalid extension package: index.js not found")
+		return nil, fmt.Errorf("invalid extension package: index.js not found")
 	}
 
 	newManifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid extension manifest: %w", err)
+		return nil, fmt.Errorf("invalid extension manifest: %w", err)
 	}
 
 	m.mu.RLock()
@@ -804,15 +804,15 @@ func (m *extensionManager) UpgradeExtension(filePath string) (*loadedExtension,
 	m.mu.RUnlock()
 
 	if !exists {
-		return nil, fmt.Errorf("Extension '%s' is not installed. Use install instead of upgrade.", newManifest.DisplayName)
+		return nil, fmt.Errorf("extension '%s' is not installed; use install instead of upgrade", newManifest.DisplayName)
 	}
 
 	versionCompare := compareVersions(newManifest.Version, existing.Manifest.Version)
 	if versionCompare < 0 {
-		return nil, fmt.Errorf("Cannot downgrade extension. Current version: %s, New version: %s", existing.Manifest.Version, newManifest.Version)
+		return nil, fmt.Errorf("cannot downgrade extension: current version: %s, new version: %s", existing.Manifest.Version, newManifest.Version)
 	}
 	if versionCompare == 0 {
-		return nil, fmt.Errorf("Extension is already at version %s", existing.Manifest.Version)
+		return nil, fmt.Errorf("extension is already at version %s", existing.Manifest.Version)
 	}
 
 	GoLog("[Extension] Upgrading %s from v%s to v%s\n", newManifest.DisplayName, existing.Manifest.Version, newManifest.Version)
@@ -906,13 +906,13 @@ type ExtensionUpgradeInfo struct {
 
 func (m *extensionManager) checkExtensionUpgradeInternal(filePath string) (*ExtensionUpgradeInfo, error) {
 	if !strings.HasSuffix(strings.ToLower(filePath), ".spotiflac-ext") {
-		return nil, fmt.Errorf("Invalid file format. Please select a .spotiflac-ext file")
+		return nil, fmt.Errorf("invalid file format: please select a .spotiflac-ext file")
 	}
 
 	zipReader, err := zip.OpenReader(filePath)
 
 	if err != nil {
-		return nil, fmt.Errorf("Cannot open extension file")
+		return nil, fmt.Errorf("cannot open extension file")
 	}
 	defer zipReader.Close()
 
@@ -939,7 +939,7 @@ func (m *extensionManager) checkExtensionUpgradeInternal(filePath string) (*Exte
 
 	newManifest, err := ParseManifest(manifestData)
 	if err != nil {
-		return nil, fmt.Errorf("Invalid manifest: %w", err)
+		return nil, fmt.Errorf("invalid manifest: %w", err)
 	}
 
 	m.mu.RLock()
@@ -1082,7 +1082,7 @@ func (m *extensionManager) InitializeExtension(extensionID string, settings map[
 
 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}
 
 	ext.VMMu.Lock()
@@ -1100,7 +1100,7 @@ func (m *extensionManager) CleanupExtension(extensionID string) error {
 
 	ext, exists := m.extensions[extensionID]
 	if !exists {
-		return fmt.Errorf("Extension not found")
+		return fmt.Errorf("extension not found")
 	}
 
 	if ext.VM == nil {
diff --git a/go_backend/extension_providers.go b/go_backend/extension_providers.go
index 0aac5418..33f5f539 100644
--- a/go_backend/extension_providers.go
+++ b/go_backend/extension_providers.go
@@ -3333,11 +3333,7 @@ func (p *extensionProviderWrapper) FetchLyrics(trackName, artistName, albumName
 	}
 
 	for _, line := range extResult.Lines {
-		response.Lines = append(response.Lines, LyricsLine{
-			StartTimeMs: line.StartTimeMs,
-			Words:       line.Words,
-			EndTimeMs:   line.EndTimeMs,
-		})
+		response.Lines = append(response.Lines, LyricsLine(line))
 	}
 
 	if len(response.Lines) == 0 && response.PlainLyrics != "" && !response.Instrumental {
diff --git a/go_backend/extension_runtime_binary.go b/go_backend/extension_runtime_binary.go
index 07535420..1fb02c17 100644
--- a/go_backend/extension_runtime_binary.go
+++ b/go_backend/extension_runtime_binary.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/dop251/goja"
+	//lint:ignore SA1019 Blowfish is required for legacy extension crypto compatibility.
 	"golang.org/x/crypto/blowfish"
 )
 
diff --git a/go_backend/extension_runtime_storage.go b/go_backend/extension_runtime_storage.go
index 541e67ba..86f95c3c 100644
--- a/go_backend/extension_runtime_storage.go
+++ b/go_backend/extension_runtime_storage.go
@@ -340,16 +340,6 @@ func (r *extensionRuntime) ensureCredentialsLoaded() error {
 	return nil
 }
 
-func (r *extensionRuntime) loadCredentials() (map[string]interface{}, error) {
-	if err := r.ensureCredentialsLoaded(); err != nil {
-		return nil, err
-	}
-
-	r.credentialsMu.RLock()
-	defer r.credentialsMu.RUnlock()
-	return cloneInterfaceMap(r.credentialsCache), nil
-}
-
 func (r *extensionRuntime) saveCredentials(creds map[string]interface{}) error {
 	data, err := json.Marshal(creds)
 	if err != nil {
diff --git a/go_backend/httputil_utls.go b/go_backend/httputil_utls.go
index 8c9c721a..1ef51979 100644
--- a/go_backend/httputil_utls.go
+++ b/go_backend/httputil_utls.go
@@ -10,16 +10,13 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
-	"sync"
 
 	utls "github.com/refraction-networking/utls"
 	"golang.org/x/net/http2"
 )
 
 type utlsTransport struct {
-	dialer       *net.Dialer
-	mu           sync.Mutex
-	h2Transports map[string]*http2.Transport
+	dialer *net.Dialer
 }
 
 func newUTLSTransport() *utlsTransport {
@@ -28,7 +25,6 @@ func newUTLSTransport() *utlsTransport {
 			Timeout:   30 * Second,
 			KeepAlive: 30 * Second,
 		},
-		h2Transports: make(map[string]*http2.Transport),
 	}
 }
 
diff --git a/go_backend/library_scan.go b/go_backend/library_scan.go
index e1752d9a..ea153256 100644
--- a/go_backend/library_scan.go
+++ b/go_backend/library_scan.go
@@ -276,18 +276,10 @@ func ScanLibraryFolder(folderPath string) (string, error) {
 	return string(jsonBytes), nil
 }
 
-func scanAudioFile(filePath, scanTime string) (*LibraryScanResult, error) {
-	return scanAudioFileWithKnownModTimeAndDisplayName(filePath, "", scanTime, 0)
-}
-
 func scanAudioFileWithKnownModTime(filePath, scanTime string, knownModTime int64) (*LibraryScanResult, error) {
 	return scanAudioFileWithKnownModTimeAndDisplayNameAndCoverCacheKey(filePath, "", "", scanTime, knownModTime)
 }
 
-func scanAudioFileWithKnownModTimeAndDisplayName(filePath, displayNameHint, scanTime string, knownModTime int64) (*LibraryScanResult, error) {
-	return scanAudioFileWithKnownModTimeAndDisplayNameAndCoverCacheKey(filePath, displayNameHint, "", scanTime, knownModTime)
-}
-
 func scanAudioFileWithKnownModTimeAndDisplayNameAndCoverCacheKey(filePath, displayNameHint, coverCacheKey, scanTime string, knownModTime int64) (*LibraryScanResult, error) {
 	ext := resolveLibraryAudioExt(filePath, displayNameHint)
 
diff --git a/go_backend/lyrics_musixmatch.go b/go_backend/lyrics_musixmatch.go
index 309f5480..027188de 100644
--- a/go_backend/lyrics_musixmatch.go
+++ b/go_backend/lyrics_musixmatch.go
@@ -16,32 +16,6 @@ type MusixmatchClient struct {
 	baseURL    string
 }
 
-type musixmatchSearchResponse struct {
-	ID                 int64                     `json:"id"`
-	SongName           string                    `json:"songName"`
-	ArtistName         string                    `json:"artistName"`
-	AlbumName          string                    `json:"albumName"`
-	Artwork            string                    `json:"artwork"`
-	ReleaseDate        string                    `json:"releaseDate"`
-	Duration           int                       `json:"duration"`
-	URL                string                    `json:"url"`
-	AlbumID            int64                     `json:"albumId"`
-	HasSyncedLyrics    bool                      `json:"hasSyncedLyrics"`
-	HasUnsyncedLyrics  bool                      `json:"hasUnsyncedLyrics"`
-	AvailableLanguages []string                  `json:"availableLanguages"`
-	OriginalLanguage   string                    `json:"originalLanguage"`
-	SyncedLyrics       *musixmatchLyricsResponse `json:"syncedLyrics"`
-	UnsyncedLyrics     *musixmatchLyricsResponse `json:"unsyncedLyrics"`
-}
-
-type musixmatchLyricsResponse struct {
-	ID          int64  `json:"id"`
-	Duration    int    `json:"duration"`
-	Language    string `json:"language"`
-	UpdatedTime string `json:"updatedTime"`
-	Lyrics      string `json:"lyrics"`
-}
-
 func NewMusixmatchClient() *MusixmatchClient {
 	return &MusixmatchClient{
 		httpClient: NewMetadataHTTPClient(15 * time.Second),
diff --git a/go_backend/metadata.go b/go_backend/metadata.go
index 6ac35adf..cfa8432e 100644
--- a/go_backend/metadata.go
+++ b/go_backend/metadata.go
@@ -1150,17 +1150,6 @@ func readM4ATextValue(f *os.File, parent atomHeader, fileSize int64) (string, er
 	return strings.TrimSpace(strings.TrimRight(string(payload), "\x00")), nil
 }
 
-func readM4AIndexValue(f *os.File, parent atomHeader, fileSize int64) (int, error) {
-	payload, err := readM4ADataPayload(f, parent, fileSize)
-	if err != nil {
-		return 0, err
-	}
-	if len(payload) < 4 {
-		return 0, fmt.Errorf("index payload too short in %s", parent.typ)
-	}
-	return int(binary.BigEndian.Uint16(payload[2:4])), nil
-}
-
 func readM4AIndexPair(f *os.File, parent atomHeader, fileSize int64) (int, int, error) {
 	payload, err := readM4ADataPayload(f, parent, fileSize)
 	if err != nil {
diff --git a/go_backend/progress.go b/go_backend/progress.go
index 6fc20b65..5837dfb4 100644
--- a/go_backend/progress.go
+++ b/go_backend/progress.go
@@ -56,9 +56,6 @@ type progressBridgeState struct {
 }
 
 var (
-	downloadDir   string
-	downloadDirMu sync.RWMutex
-
 	multiProgress       = MultiProgress{Items: make(map[string]*ItemProgress)}
 	multiMu             sync.RWMutex
 	multiProgressDirty  = true
@@ -368,9 +365,6 @@ func ClearAllItemProgress() {
 }
 
 func setDownloadDir(path string) error {
-	downloadDirMu.Lock()
-	defer downloadDirMu.Unlock()
-	downloadDir = path
 	return nil
 }
 
diff --git a/go_backend/title_match_utils.go b/go_backend/title_match_utils.go
index 00da7e08..52ecaeb4 100644
--- a/go_backend/title_match_utils.go
+++ b/go_backend/title_match_utils.go
@@ -138,11 +138,7 @@ func artistsMatch(expectedArtist, foundArtist string) bool {
 		}
 	}
 
-	if isLatinScript(expectedArtist) != isLatinScript(foundArtist) {
-		return true
-	}
-
-	return false
+	return isLatinScript(expectedArtist) != isLatinScript(foundArtist)
 }
 
 func splitArtists(artists string) []string {