Add Apple Intelligence language-fallback settings

Cotabby/App/Core/AppDelegate.swift

@@ -83,9 +83,14 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
             }
             .store(in: &cancellables)
 
-        suggestionSettings.$selectedEngine
+        // The fallback switches decide whether the local model stays loaded under Apple Intelligence,
+        // so they re-evaluate the runtime just like an engine change does.
+        Publishers.CombineLatest3(
+            suggestionSettings.$selectedEngine.removeDuplicates(),
+            suggestionSettings.$isAppleLanguageFallbackEnabled.removeDuplicates(),
+            suggestionSettings.$keepsFallbackModelLoaded.removeDuplicates()
+        )
             .dropFirst()
-            .removeDuplicates()
             .sink { [weak self] _ in
                 self?.startRuntimeIfPreferredEngineRequiresIt()
             }
@@ -284,6 +289,11 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         switch suggestionSettings.selectedEngine {
         case .llamaOpenSource:
             runtimeModel.startIfNeeded()
+        case .appleIntelligence
+            where suggestionSettings.isAppleLanguageFallbackEnabled && suggestionSettings.keepsFallbackModelLoaded:
+            // The user chose to keep the fallback model ready, so an unsupported language gets a
+            // suggestion without first waiting several seconds for the model to load.
+            runtimeModel.startIfNeeded()
         case .appleIntelligence, .openAICompatible:
             // Switching away must release Metal buffers and the mapped GGUF. Otherwise an Ollama
             // user still pays the duplicate memory cost the external endpoint is meant to avoid.

Cotabby/Models/Settings/SuggestionSettingsData.swift

@@ -28,6 +28,11 @@ struct SuggestionEngineSettings: Equatable {
     var pluggedInEngine: SuggestionEngineKind
     var pluggedInModelFilename: String
     var pluggedInEndpointModelName: String
+    /// When Apple Intelligence rejects a language, retry with the selected Open Source model.
+    var isAppleLanguageFallbackEnabled: Bool
+    /// Keep that fallback model loaded while Apple Intelligence is selected, so the first
+    /// fallback suggestion does not wait for the model to load. Costs the model's memory.
+    var keepsFallbackModelLoaded: Bool
 }
 
 /// Completion length, timing, streaming, and acceptance behavior.
@@ -185,6 +190,16 @@ extension SuggestionSettingsData {
         set { engine.isPowerBasedModelSwitchingEnabled = newValue }
     }
 
+    var isAppleLanguageFallbackEnabled: Bool {
+        get { engine.isAppleLanguageFallbackEnabled }
+        set { engine.isAppleLanguageFallbackEnabled = newValue }
+    }
+
+    var keepsFallbackModelLoaded: Bool {
+        get { engine.keepsFallbackModelLoaded }
+        set { engine.keepsFallbackModelLoaded = newValue }
+    }
+
     var batteryEngine: SuggestionEngineKind {
         get { engine.batteryEngine }
         set { engine.batteryEngine = newValue }

Cotabby/Models/Settings/SuggestionSettingsModel.swift

@@ -158,6 +158,11 @@ final class SuggestionSettingsModel: ObservableObject {
     @Published private(set) var perAppShortcutOverrides: [PerAppShortcutOverride]
     @Published private(set) var acceptanceGranularity: AcceptanceGranularity
     @Published private(set) var isPowerBasedModelSwitchingEnabled: Bool
+    /// Retry with the Open Source model when Apple Intelligence rejects the text's language.
+    /// Read live by `SuggestionEngineRouter` at request time.
+    @Published private(set) var isAppleLanguageFallbackEnabled: Bool
+    /// Keep the fallback model loaded while Apple Intelligence is selected (see `AppDelegate`).
+    @Published private(set) var keepsFallbackModelLoaded: Bool
     @Published private(set) var batteryEngine: SuggestionEngineKind
     @Published private(set) var batteryModelFilename: String
     @Published private(set) var batteryEndpointModelName: String
@@ -286,6 +291,8 @@ final class SuggestionSettingsModel: ObservableObject {
         perAppShortcutOverrides = data.perAppShortcutOverrides
         acceptanceGranularity = data.acceptanceGranularity
         isPowerBasedModelSwitchingEnabled = data.isPowerBasedModelSwitchingEnabled
+        isAppleLanguageFallbackEnabled = data.isAppleLanguageFallbackEnabled
+        keepsFallbackModelLoaded = data.keepsFallbackModelLoaded
         batteryEngine = data.batteryEngine
         batteryModelFilename = data.batteryModelFilename
         batteryEndpointModelName = data.batteryEndpointModelName
@@ -369,6 +376,8 @@ final class SuggestionSettingsModel: ObservableObject {
         perAppShortcutOverrides = data.perAppShortcutOverrides
         acceptanceGranularity = data.acceptanceGranularity
         isPowerBasedModelSwitchingEnabled = data.isPowerBasedModelSwitchingEnabled
+        isAppleLanguageFallbackEnabled = data.isAppleLanguageFallbackEnabled
+        keepsFallbackModelLoaded = data.keepsFallbackModelLoaded
         batteryEngine = data.batteryEngine
         batteryModelFilename = data.batteryModelFilename
         batteryEndpointModelName = data.batteryEndpointModelName
@@ -410,7 +419,9 @@ final class SuggestionSettingsModel: ObservableObject {
                 batteryEndpointModelName: batteryEndpointModelName,
                 pluggedInEngine: pluggedInEngine,
                 pluggedInModelFilename: pluggedInModelFilename,
-                pluggedInEndpointModelName: pluggedInEndpointModelName
+                pluggedInEndpointModelName: pluggedInEndpointModelName,
+                isAppleLanguageFallbackEnabled: isAppleLanguageFallbackEnabled,
+                keepsFallbackModelLoaded: keepsFallbackModelLoaded
             ),
             completion: SuggestionCompletionSettings(
                 selectedWordCountPreset: selectedWordCountPreset,
@@ -571,6 +582,18 @@ final class SuggestionSettingsModel: ObservableObject {
         endpointCredentialRevision &+= 1
     }
 
+    func setAppleLanguageFallbackEnabled(_ enabled: Bool) {
+        guard isAppleLanguageFallbackEnabled != enabled else { return }
+        isAppleLanguageFallbackEnabled = enabled
+        store.saveAppleLanguageFallbackEnabled(enabled)
+    }
+
+    func setKeepsFallbackModelLoaded(_ enabled: Bool) {
+        guard keepsFallbackModelLoaded != enabled else { return }
+        keepsFallbackModelLoaded = enabled
+        store.saveKeepsFallbackModelLoaded(enabled)
+    }
+
     func setPowerBasedModelSwitchingEnabled(_ enabled: Bool) {
         guard isPowerBasedModelSwitchingEnabled != enabled else {
             return

Cotabby/Services/Runtime/SuggestionEngineRouter.swift

@@ -62,6 +62,18 @@ final class SuggestionEngineRouter {
                 recordQualityOutcome(result)
                 return result
             } catch SuggestionClientError.unsupportedLanguageOrLocale(let message) {
+                // The user can turn the fallback off (Engine & Model → Apple Intelligence). Then an
+                // unsupported language simply gets no suggestion, and the local model never loads.
+                guard suggestionSettings.isAppleLanguageFallbackEnabled else {
+                    CotabbyLogger.suggestion.info(
+                        "Apple Intelligence unsupported for locale; fallback is turned off",
+                        metadata: metadata.merging(["reason": .string(message)]) { _, new in new }
+                    )
+                    return SuggestionResult(
+                        generation: request.generation, rawText: "", text: "", latency: 0,
+                        suppressionReason: "appleLanguageUnsupported"
+                    )
+                }
                 CotabbyLogger.suggestion.info(
                     "Apple Intelligence unsupported for locale, falling back to open-source: \(message)",
                     metadata: metadata.merging([

Cotabby/Support/Runtime/BundledRuntimeLocator.swift

@@ -103,8 +103,12 @@ struct BundledRuntimeLocator {
     /// them out of the model picker.
     static func discoverGGUFModelURLs(in directoryURL: URL, maxDepth: Int = 4) -> [URL] {
         let fileManager = FileManager.default
+        // `FileManager.enumerator` does not descend into a root that is itself a symbolic link, so a
+        // models folder linked to another location (an external drive, another app's folder) would
+        // list nothing. Resolve the root first; links deeper inside stay unfollowed, which keeps
+        // the bounded walk from escaping into arbitrary trees.
         guard let enumerator = fileManager.enumerator(
-            at: directoryURL,
+            at: directoryURL.resolvingSymlinksInPath(),
             includingPropertiesForKeys: [.isRegularFileKey],
             options: [.skipsHiddenFiles, .skipsPackageDescendants]
         ) else {

Cotabby/Support/Settings/SuggestionSettingsStore.swift

@@ -189,6 +189,8 @@ struct SuggestionSettingsStore {
     private static let globalToggleKeyLabelDefaultsKey = "cotabbyGlobalToggleKeyLabel"
     private static let acceptanceGranularityDefaultsKey = "cotabbyAcceptanceGranularity"
 
+    private static let appleLanguageFallbackEnabledDefaultsKey = "cotabbyAppleLanguageFallbackEnabled"
+    private static let keepFallbackModelLoadedDefaultsKey = "cotabbyKeepFallbackModelLoaded"
     private static let powerModelSwitchingEnabledDefaultsKey = "cotabbyPowerBasedModelSwitchingEnabled"
     private static let batteryEngineDefaultsKey = "cotabbyBatteryEngine"
     private static let batteryModelFilenameDefaultsKey = "cotabbyBatteryModelFilename"
@@ -270,6 +272,8 @@ struct SuggestionSettingsStore {
         globalToggleKeyLabelDefaultsKey,
         acceptanceGranularityDefaultsKey,
         powerModelSwitchingEnabledDefaultsKey,
+        appleLanguageFallbackEnabledDefaultsKey,
+        keepFallbackModelLoadedDefaultsKey,
         batteryEngineDefaultsKey,
         batteryModelFilenameDefaultsKey,
         batteryEndpointModelNameDefaultsKey,
@@ -549,6 +553,11 @@ struct SuggestionSettingsStore {
 
         let resolvedPowerBasedModelSwitchingEnabled =
             userDefaults.object(forKey: Self.powerModelSwitchingEnabledDefaultsKey) as? Bool ?? false
+        // On by default: falling back is what Cotabby has always done for unsupported languages.
+        let resolvedAppleLanguageFallbackEnabled =
+            userDefaults.object(forKey: Self.appleLanguageFallbackEnabledDefaultsKey) as? Bool ?? true
+        let resolvedKeepsFallbackModelLoaded =
+            userDefaults.object(forKey: Self.keepFallbackModelLoadedDefaultsKey) as? Bool ?? false
         let resolvedBatteryEngine = userDefaults.string(forKey: Self.batteryEngineDefaultsKey)
             .flatMap(SuggestionEngineKind.init(rawValue:)) ?? .llamaOpenSource
         let resolvedBatteryModelFilename = userDefaults.string(forKey: Self.batteryModelFilenameDefaultsKey) ?? ""
@@ -580,7 +589,9 @@ struct SuggestionSettingsStore {
                 batteryEndpointModelName: resolvedBatteryEndpointModelName,
                 pluggedInEngine: resolvedPluggedInEngine,
                 pluggedInModelFilename: resolvedPluggedInModelFilename,
-                pluggedInEndpointModelName: resolvedPluggedInEndpointModelName
+                pluggedInEndpointModelName: resolvedPluggedInEndpointModelName,
+                isAppleLanguageFallbackEnabled: resolvedAppleLanguageFallbackEnabled,
+                keepsFallbackModelLoaded: resolvedKeepsFallbackModelLoaded
             ),
             completion: SuggestionCompletionSettings(
                 selectedWordCountPreset: resolvedWordCountPreset,
@@ -724,6 +735,8 @@ struct SuggestionSettingsStore {
         savePerAppShortcutOverrides(data.perAppShortcutOverrides)
         saveAcceptanceGranularity(data.acceptanceGranularity)
         savePowerBasedModelSwitchingEnabled(data.isPowerBasedModelSwitchingEnabled)
+        saveAppleLanguageFallbackEnabled(data.isAppleLanguageFallbackEnabled)
+        saveKeepsFallbackModelLoaded(data.keepsFallbackModelLoaded)
         saveBatteryEngine(data.batteryEngine)
         saveBatteryModelFilename(data.batteryModelFilename)
         saveBatteryEndpointModelName(data.batteryEndpointModelName)
@@ -851,6 +864,14 @@ struct SuggestionSettingsStore {
         userDefaults.set(mode.rawValue, forKey: Self.openAICompatibleAPIModeDefaultsKey)
     }
 
+    func saveAppleLanguageFallbackEnabled(_ enabled: Bool) {
+        userDefaults.set(enabled, forKey: Self.appleLanguageFallbackEnabledDefaultsKey)
+    }
+
+    func saveKeepsFallbackModelLoaded(_ enabled: Bool) {
+        userDefaults.set(enabled, forKey: Self.keepFallbackModelLoadedDefaultsKey)
+    }
+
     func savePowerBasedModelSwitchingEnabled(_ enabled: Bool) {
         userDefaults.set(enabled, forKey: Self.powerModelSwitchingEnabledDefaultsKey)
     }

Cotabby/UI/Settings/Panes/Engine/EngineAndModelPaneView+AppleIntelligence.swift

@@ -1,3 +1,4 @@
+import Foundation
 import SwiftUI
 
 /// Apple Intelligence availability presentation.
@@ -23,6 +24,64 @@ extension EngineAndModelPaneView {
                 )
             }
             .settingsItem(.appleIntelligenceAvailability)
+
+            Toggle(isOn: Binding(
+                get: { suggestionSettings.isAppleLanguageFallbackEnabled },
+                set: { suggestionSettings.setAppleLanguageFallbackEnabled($0) }
+            )) {
+                SettingsRowLabel(
+                    title: "Fall Back to Open Source Model",
+                    description: "When Apple Intelligence doesn't support the language you're writing in, " +
+                        "suggest with \(fallbackModelName) instead. Turn off to get no suggestion in those languages.",
+                    systemImage: "arrow.triangle.branch"
+                )
+            }
+            .settingsItem(.appleLanguageFallback)
+
+            Toggle(isOn: Binding(
+                get: { suggestionSettings.keepsFallbackModelLoaded },
+                set: { suggestionSettings.setKeepsFallbackModelLoaded($0) }
+            )) {
+                SettingsRowLabel(
+                    title: "Keep Fallback Model Loaded",
+                    description: "Load the fallback model in advance so its first suggestion doesn't wait for it " +
+                        "to load. Uses the model's memory (several GB) while Apple Intelligence is selected.",
+                    systemImage: "memorychip"
+                )
+            }
+            .disabled(!suggestionSettings.isAppleLanguageFallbackEnabled)
+
+            // The Open Source section is hidden while Apple Intelligence is the engine, so the
+            // fallback model is chosen here. It is the same selection the Open Source engine uses:
+            // the local runtime holds one model at a time.
+            if runtimeModel.availableModels.isEmpty {
+                Text("No downloaded models were found, so there is nothing to fall back to. " +
+                    "Switch the engine to Open Source to download one.")
+                    .font(.caption)
+                    .foregroundStyle(.orange)
+            } else {
+                Picker(selection: selectedModelBinding) {
+                    ForEach(runtimeModel.availableModels) { model in
+                        Text(model.displayName).tag(model.filename)
+                    }
+                } label: {
+                    SettingsRowLabel(
+                        title: "Fallback Model",
+                        description: "The downloaded model used when Apple Intelligence can't handle the " +
+                            "language. It is also your Open Source engine's model.",
+                        systemImage: "shippingbox"
+                    )
+                }
+                .disabled(!suggestionSettings.isAppleLanguageFallbackEnabled
+                    || suggestionSettings.isPowerBasedModelSwitchingEnabled)
+                .settingsItem(.appleLanguageFallbackModel)
+            }
         }
     }
+
+    /// The model the fallback uses: the selected Open Source model. The local runtime holds one
+    /// model at a time, so the fallback cannot use a different one without swapping it in.
+    private var fallbackModelName: String {
+        runtimeModel.selectedModelFilename.map { ($0 as NSString).deletingPathExtension } ?? "your Open Source model"
+    }
 }

Cotabby/UI/Settings/SettingsIndex.swift

@@ -63,6 +63,8 @@ enum SettingsItem: String, CaseIterable, Identifiable {
     // Engine & Model
     case engine
     case appleIntelligenceAvailability
+    case appleLanguageFallback
+    case appleLanguageFallbackModel
     case modelStatus
     case selectedModel
     case lowPowerModeAutoDisable
@@ -152,6 +154,8 @@ enum SettingsItem: String, CaseIterable, Identifiable {
         case .contextLivePreview: return "Live Preview"
         case .engine: return "Engine"
         case .appleIntelligenceAvailability: return "Apple Intelligence Availability"
+        case .appleLanguageFallback: return "Fall Back to Open Source Model"
+        case .appleLanguageFallbackModel: return "Fallback Model"
         case .modelStatus: return "Model Status"
         case .selectedModel: return "Selected Model"
         case .lowPowerModeAutoDisable: return "Pause in Low Power Mode"
@@ -236,6 +240,8 @@ enum SettingsItem: String, CaseIterable, Identifiable {
         case .contextLivePreview: return "text.cursor"
         case .engine: return "cpu"
         case .appleIntelligenceAvailability: return "apple.logo"
+        case .appleLanguageFallback: return "arrow.triangle.branch"
+        case .appleLanguageFallbackModel: return "shippingbox"
         case .modelStatus: return "info.circle"
         case .selectedModel: return "shippingbox"
         case .lowPowerModeAutoDisable: return "bolt.slash.circle"
@@ -293,7 +299,7 @@ enum SettingsItem: String, CaseIterable, Identifiable {
             return .writing
         case .extendedContext, .contextLivePreview:
             return .context
-        case .engine, .appleIntelligenceAvailability, .modelStatus, .selectedModel,
+        case .engine, .appleIntelligenceAvailability, .appleLanguageFallback, .appleLanguageFallbackModel, .modelStatus, .selectedModel,
              .lowPowerModeAutoDisable, .powerBasedModelSwitching, .batteryModel, .pluggedInModel,
              .downloadModels, .huggingFaceBrowser, .modelsFolder, .lmStudio,
              .endpointBaseURL, .endpointAPIMode, .endpointAPIKey, .endpointStatus, .endpointModel:
@@ -363,6 +369,8 @@ enum SettingsItem: String, CaseIterable, Identifiable {
         case .contextLivePreview: return "A real field that exercises the full pipeline."
         case .engine: return "Apple Intelligence, bundled Open Source, or a local endpoint."
         case .appleIntelligenceAvailability: return "Whether this Mac can run Apple Intelligence."
+        case .appleLanguageFallback: return "Use the local model for languages Apple Intelligence doesn't support."
+        case .appleLanguageFallbackModel: return "Which downloaded model the language fallback uses."
         case .modelStatus: return "Whether the local model is loaded and ready."
         case .selectedModel: return "Which downloaded model generates suggestions."
         case .lowPowerModeAutoDisable: return "Pause suggestions while Low Power Mode is active."
@@ -537,6 +545,11 @@ enum SettingsItem: String, CaseIterable, Identifiable {
                     "provider", "runtime", "foundation models", "oss", "local", "endpoint",
                     "ollama", "openai compatible", "lm studio", "vllm",
                     "on-device", "model engine"]
+        case .appleLanguageFallbackModel:
+            return ["fallback model", "fallback", "model", "gemma", "gguf", "local model", "choose model"]
+        case .appleLanguageFallback:
+            return ["fallback", "fall back", "unsupported language", "language", "macedonian",
+                    "open source", "local model", "gemma", "llama", "keep loaded", "preload", "memory"]
         case .appleIntelligenceAvailability:
             return ["apple intelligence", "availability", "available", "supported",
                     "compatibility", "status", "macos", "device support"]