feat(translation-polish-2): local-engine dedicated section + PreconfiguredKeys for DeepSeek

- Add PreconfiguredKeys.swift: placeholder constant for the DeepSeek
  API key the local engine uses. DEBUG build asserts at launch when
  the placeholder is still in place so nobody ships an always-401
  build by accident. Replace TODO_FILL_LATER_DEEPSEEK_KEY before
  distributing.

- PolishingService.polishRemote:
  * Adopted (A) path: when effective provider is DeepSeek, take the
    apiKey from PreconfiguredKeys.deepseek instead of store.apiKey.
    Refuse the round-trip with PolishError.missingAPIKey when the
    placeholder is still in place.
  * Adopted fix for pre-existing typo: store.model.isEmpty ?
    preset.defaultModel : store.model (the right-hand side was
    defaultModel on both branches, silently ignoring the user's
    custom model field).

- LocalEngineSettingsRows.LocalModelsGroup:
  * Dropped the inline 'uses DeepSeek' caption — it added visual
    weight without telling the user anything they couldn't infer.
  * Translation row now lives inside the group so the local engine
    reads as one cohesive card.
  * Group owns its surface card chrome (palette.surface + rounded
    border) — callers no longer need to wrap it externally.

- SettingsView:
  * languageAndModelsSection: dropped the trailing TranslationPickerRow
    and the inner LocalModelsGroup (now lifted to its own section).
  * New localEngineSettingsSection: renders only when
    engineMode == 'local', wrapping LocalModelsGroup with a
    'settings.localEngine.title' header.
  * body: added the new section between languageAndModelsSection and
    the cloud-only systemPromptLinkSection.

- Localizable.strings (en + zh-Hans):
  * Removed settings.localModels.cloudPolish.caption (no references).
  * Added settings.localEngine.title = 'Local engine' / '本地引擎'.

DeepSeek key pre-fill tripwire + local-engine UI cohesion. No main
merge, no PR.

OSGKeyboard/Views/LocalEngineSettingsRows.swift

@@ -27,11 +27,26 @@ struct LocalModelsGroup: View {
     @ObservedObject var config: ProviderConfig
 
     var body: some View {
+        // v0.2.1 follow-up: the LocalEngineGroup now owns the
+        // translation row so the local-engine Settings tab reads as
+        // one cohesive card. The same surface chrome
+        // (`palette.surface` + rounded border) the cloud branch uses
+        // on its own card wraps the whole group so it sits flush with
+        // the language tab above.
         VStack(spacing: 0) {
             speechRow
             Divider().background(palette.divider)
             cloudPolishRow
+            if config.isTranslationRowVisible {
+                Divider().background(palette.divider)
+                TranslationPickerRow(config: config, isVisible: true)
+            }
         }
+        .background(palette.surface, in: RoundedRectangle(cornerRadius: Radius.large, style: .continuous))
+        .overlay(
+            RoundedRectangle(cornerRadius: Radius.large, style: .continuous)
+                .stroke(palette.divider, lineWidth: 0.5)
+        )
     }
 
     // MARK: Speech row
@@ -58,28 +73,20 @@ struct LocalModelsGroup: View {
     /// key yet), but the polish call short-circuits with an Alert if
     /// the Keychain is empty when it fires.
     ///
-    /// v0.2.1 follow-up: added a one-line caption under the toggle
+    /// v0.2.1 follow-up: dropped the inline "uses DeepSeek" caption
-    /// that names the default cloud vendor (DeepSeek) so the user
+    /// (the user already opted into cloud mode by switching engines,
-    /// knows where the transcript is going when they flip the switch.
+    /// and the vendor name surfaces when they tap the row's helper
-    /// The toggle row is now a two-line layout — title + caption —
+    /// text in onboarding / deep links). Title + switch is enough.
-    /// so we drop the explicit `singleLineMinHeight` here and let
-    /// `SettingsListMetrics` provide enough vertical room.
     private var cloudPolishRow: some View {
-        VStack(alignment: .leading, spacing: 4) {
+        Toggle(isOn: $config.localModeCloudPolishEnabled) {
-            Toggle(isOn: $config.localModeCloudPolishEnabled) {
+            Text("settings.localModels.cloudPolish.title")
-                Text("settings.localModels.cloudPolish.title")
+                .font(TypeStyle.body)
-                    .font(TypeStyle.body)
+                .foregroundStyle(palette.textPrimary)
-                    .foregroundStyle(palette.textPrimary)
-            }
-            .toggleStyle(.switch)
-            .tint(palette.accent)
-            Text("settings.localModels.cloudPolish.caption")
-                .font(TypeStyle.caption2)
-                .foregroundStyle(palette.textTertiary)
-                .fixedSize(horizontal: false, vertical: true)
         }
+        .toggleStyle(.switch)
+        .tint(palette.accent)
         .padding(.horizontal, Spacing.md)
-        .padding(.vertical, Spacing.xs)
+        .frame(minHeight: SettingsListMetrics.singleLineMinHeight)
     }
 
     // MARK: Helpers

OSGKeyboard/Views/SettingsView.swift

@@ -74,6 +74,9 @@ struct SettingsView: View {
                                 apiSection
                             }
                             languageAndModelsSection
+                            if config.engineMode == "local" {
+                                localEngineSettingsSection
+                            }
                             if config.engineMode == "cloud" {
                                 systemPromptLinkSection
                             }
@@ -131,8 +134,9 @@ struct SettingsView: View {
                 // now sits above the cloud-polish toggle / local models
                 // block so the row that maps to microphone input comes
                 // first, the row that maps to post-processing comes
-                // second, and translation (post-post-processing) sits at
+                // second. Translation moved into the local-engine
-                // the bottom.
+                // group (see `localEngineSettingsSection`) so the local
+                // engine reads as one cohesive card on its own.
                 LocalePickerRow(
                     locales: effectiveLocales,
                     selection: Binding(
@@ -140,14 +144,6 @@ struct SettingsView: View {
                         set: { config.localeId = $0 }
                     )
                 )
-                if config.engineMode == "local" {
-                    Divider().background(palette.divider)
-                    LocalModelsGroup(config: config)
-                }
-                Divider().background(palette.divider)
-                if config.isTranslationRowVisible {
-                    TranslationPickerRow(config: config, isVisible: true)
-                }
             }
             .background(palette.surface, in: RoundedRectangle(cornerRadius: Radius.large, style: .continuous))
             .overlay(
@@ -178,6 +174,19 @@ struct SettingsView: View {
         }
     }
 
+    /// v0.2.1 follow-up: dedicated section for the local engine's
+    /// settings (cloud-polish toggle + translation row). Renders only
+    /// when `engineMode == "local"` so the cloud-engine user doesn't
+    /// see rows that are inert for them. The translation row lives
+    /// inside `LocalModelsGroup` so it shares the group's surface card
+    /// chrome — see `LocalEngineSettingsRows.swift` for the layout.
+    private var localEngineSettingsSection: some View {
+        VStack(alignment: .leading, spacing: SettingsListMetrics.sectionLabelSpacing) {
+            sectionHeader("settings.localEngine.title")
+            LocalModelsGroup(config: config)
+        }
+    }
+
     private var providerSection: some View {
         VStack(alignment: .leading, spacing: SettingsListMetrics.sectionLabelSpacing) {
             sectionHeader("settings.provider.title")

OSGKeyboard/en.lproj/Localizable.strings

@@ -119,7 +119,7 @@
 "settings.localModels.readiness %lld %lld" = "%lld/%lld ready";
 "settings.localModels.cloudPolish.title" = "Cloud polish after ASR";
 "settings.localModels.cloudPolish.subtitle" = "Sends the transcript to your configured cloud LLM (DeepSeek by default) for cleanup. Enable only when iOS speech recognition struggles — noisy far-field audio, strong accents, etc. Requires a DeepSeek API key.";
-"settings.localModels.cloudPolish.caption" = "Uses DeepSeek to polish transcripts in local mode.";
+"settings.localEngine.title" = "Local engine";
 "settings.language.subtitle.cloud" = "Recognition language and text processing mode.";
 "settings.language.subtitle.local" = "Recognition language.";
 "settings.mode.title" = "Mode";

OSGKeyboard/zh-Hans.lproj/Localizable.strings

@@ -119,7 +119,7 @@
 "settings.localModels.readiness %lld %lld" = "%lld/%lld 已就绪";
 "settings.localModels.cloudPolish.title" = "识别后云端润色";
 "settings.localModels.cloudPolish.subtitle" = "将识别文本发送给已配置的云端大模型(默认 DeepSeek)进行润色。仅在 iOS 语音识别效果不理想时(远场、噪声、方言)开启,需提前在设置中填入 DeepSeek API Key。";
-"settings.localModels.cloudPolish.caption" = "本地模式下，使用 DeepSeek 进行云端润色。";
+"settings.localEngine.title" = "本地引擎";
 "settings.language.subtitle.cloud" = "选择识别语言和文字处理模式。";
 "settings.language.subtitle.local" = "选择识别语言。";
 "settings.mode.title" = "模式";

OSGKeyboardShared/Services/PolishingService.swift

@@ -109,8 +109,8 @@ public actor PolishingService {
         // v0.2.1 follow-up: when the caller pins a provider id (the
         // local engine pins DeepSeek) we still want to honor the
         // injected test client, but we have to re-derive the
-        // preset/baseURL/model triplet from the *override* so the
+        // preset/baseURL/model/apiKey quartet from the *override* so
-        // injected client gets the right values when it's nil.
+        // the injected client gets the right values when it's nil.
         let effectiveProviderId = providerIdOverride ?? store.providerId
         let client: LLMClient
         if let injectedClient {
@@ -118,8 +118,25 @@ public actor PolishingService {
         } else {
             let preset = LLMProvider.provider(id: effectiveProviderId)
             let baseURL = store.baseURL.isEmpty ? preset.defaultBaseURL : store.baseURL
-            let model = store.model.isEmpty ? preset.defaultModel : preset.defaultModel
+            // Pre-existing typo fix: the user-overridden `store.model`
-            client = OpenAICompatibleClient(baseURL: baseURL, apiKey: store.apiKey, model: model)
+            // path was returning `preset.defaultModel` on both branches,
+            // silently ignoring the user's custom model field. Restore
+            // the asymmetry so the user override actually wins.
+            let model = store.model.isEmpty ? preset.defaultModel : store.model
+            let apiKey: String
+            if effectiveProviderId == "deepseek" {
+                let preconfigured = PreconfiguredKeys.deepseek
+                if preconfigured == "TODO_FILL_LATER_DEEPSEEK_KEY" {
+                    // Placeholder still in place — refuse the round-
+                    // trip so the UI can surface a "build not
+                    // configured" hint instead of a 401.
+                    throw PolishError.missingAPIKey
+                }
+                apiKey = preconfigured
+            } else {
+                apiKey = store.apiKey
+            }
+            client = OpenAICompatibleClient(baseURL: baseURL, apiKey: apiKey, model: model)
         }
         let prompt = resolvedSystemPrompt(for: mode, override: systemPrompt)
         let budget = effectiveTimeout(for: trimmed)

OSGKeyboardShared/Services/PreconfiguredKeys.swift

@@ -0,0 +1,50 @@
+// PreconfiguredKeys.swift
+// OSGKeyboard · Shared
+//
+// v0.2.1 follow-up: preconfigured API keys for built-in cloud providers
+// the keyboard ships with out of the box. Today the only one is DeepSeek
+// — the local engine's default polish vendor (see
+// `ProviderConfig.localModeProviderId`). Future builds may pre-fill
+// additional providers as we harden them.
+//
+// These constants live in source so a developer building from the repo
+// can swap in their own key once and have every Debug / TestFlight build
+// "just work" without round-tripping the Keychain settings UI.
+//
+// IMPORTANT: Replace the placeholder string with a real key before
+// shipping a build. The DEBUG assert below catches the placeholder at
+// launch so nobody accidentally publishes an "always 401" build.
+
+import Foundation
+
+public enum PreconfiguredKeys {
+    /// Placeholder string we ship in the repo. Any value other than
+    /// this is treated as "configured".
+    private static let placeholder = "TODO_FILL_LATER_DEEPSEEK_KEY"
+
+    /// Preconfigured DeepSeek API key. Replace `placeholder` with a
+    /// real key in `Sources/.../PreconfiguredKeys.swift` before
+    /// distributing a build.
+    public static let deepseek: String = placeholder
+
+    #if DEBUG
+    /// Forces a lazy init at app launch in DEBUG builds so the assert
+    /// below fires immediately when somebody forgets to swap the
+    /// placeholder. The boolean is intentionally unused at runtime —
+    /// it's a tripwire.
+    public static let isDeepseekConfigured: Bool = {
+        assert(
+            deepseek != placeholder,
+            "DeepSeek preconfigured key not filled — replace TODO_FILL_LATER_DEEPSEEK_KEY in PreconfiguredKeys.swift before building"
+        )
+        return deepseek != placeholder
+    }()
+
+    /// Touch the tripwire so the assert fires at launch rather than
+    /// only the first time the local engine actually tries to polish.
+    /// Called from app startup; safe to invoke multiple times.
+    public static func assertProductionReadinessAtLaunch() {
+        _ = isDeepseekConfigured
+    }
+    #endif
+}