Extracted the PreviewPreinstalling service in the Sample app target into its own file and declared it as development asset.

Apps/Attendi/Catalogs/Localizable.xcstrings

@@ -2,6 +2,8 @@
   "sourceLanguage" : "en",
   "strings" : {
     "view.recording.navigation.title" : {
+      "comment" : "The title of the navigation bar in the recording view.",
+      "extractionState" : "manual",
       "localizations" : {
         "en" : {
           "stringUnit" : {
@@ -60,6 +62,9 @@
       }
     },
     "view.recording.picker.locale.title" : {
+      "comment" : "A label for the picker that selects the locale of the spoken language to transcribe.",
+      "extractionState" : "manual",
+      "isCommentAutoGenerated" : true,
       "localizations" : {
         "en" : {
           "stringUnit" : {
@@ -70,6 +75,7 @@
       }
     },
     "view.transcription.navigation.title" : {
+      "comment" : "The title of the navigation bar in the transcription modal view.",
       "extractionState" : "manual",
       "localizations" : {
         "en" : {
@@ -81,6 +87,8 @@
       }
     },
     "view.transcription.unavailable.description" : {
+      "comment" : "The description of the content unavailable view shown in the transcription modal view for an empty transcription.",
+      "extractionState" : "manual",
       "localizations" : {
         "en" : {
           "stringUnit" : {
@@ -91,6 +99,8 @@
       }
     },
     "view.transcription.unavailable.title" : {
+      "comment" : "The title of the content unavailable view shown in the transcription modal view for an empty transcription.",
+      "extractionState" : "manual",
       "localizations" : {
         "en" : {
           "stringUnit" : {

Apps/Attendi/Previews/Services/PreviewPreinstalling.swift

@@ -0,0 +1,41 @@
+import Foundation
+import Recording
+
+/// The preinstalling service used by the previews, which resolves every locale as supported and downloads nothing.
+struct PreviewPreinstalling: Preinstalling {
+
+    /// The stream of events the service emits, which finishes immediately.
+    let events: AsyncStream<PreinstallingEvent> = .init { continuation in
+        continuation.finish()
+    }
+
+    /// Simulates the preinstallation of the speech model assets of the given locale, downloading nothing.
+    ///
+    /// - Parameter locale: The locale to preinstall the speech model assets for.
+    func preinstall(
+        for locale: Locale
+    ) async {
+        // The previews preinstall no speech model assets.
+    }
+
+    /// Returns the given locale as its own supported equivalent.
+    ///
+    /// - Parameter locale: The locale to find a supported equivalent for.
+    /// - Returns: The given locale, unchanged.
+    func supportedLocale(
+        equivalentTo locale: Locale
+    ) async -> Locale? {
+        locale
+    }
+
+    /// Returns a sample of supported locales for the locale picker.
+    ///
+    /// - Returns: A pair of sample locales.
+    func supportedLocales() async -> [Locale] {
+        [
+            Locale(identifier: "en-US"),
+            Locale(identifier: "nl-NL"),
+        ]
+    }
+
+}

Apps/Attendi/Sources/View Models/ContentViewModel.swift

@@ -15,6 +15,9 @@ extension ContentView {
     /// Every picked locale kicks off ``preinstall()``, a cancellable task that preinstalls the locale's speech model assets through the
     /// preinstalling service — cancelling any download still in flight for a previously picked locale. The service's started, cancelled, and
     /// failed download events are mapped to the transient, self-dismissing notifications of the ``notifier``.
+    ///
+    /// Every collaborator is injected at initialization behind its protocol, defaulting to the on-device services: the app runs the model
+    /// against the real backends, while its unit tests and previews attach mocks and dummies without touching this type.
     @MainActor
     @Observable
     final class Model {
@@ -84,9 +87,10 @@ extension ContentView {
 
         // MARK: Methods
 
-        /// Loads the locales the transcriber supports into ``locales``, sorted by their localized names, and aligns ``locale`` with the
+        /// Loads the locales the transcriber supports — resolved through the preinstalling service — into ``locales``, sorted by their
-        /// supported equivalent of its current value — falling back to the supported equivalent of a default locale when none exists —
+        /// localized names, and aligns ``locale`` with the supported equivalent of its current value — falling back to the supported
-        /// so the locale picker starts with a valid selection.
+        /// equivalent of a default locale when none exists — so the locale picker starts with a valid selection. It then kicks off the
+        /// preinstallation of the aligned locale's speech model assets.
         func load() async {
             locales =
                 await preinstaller

Apps/Attendi/Sources/Views/ContentView.swift

@@ -12,7 +12,7 @@ import SwiftUI
 ///
 /// The services attached to the feature, the transcription shown in the sheet, and the notifier owning the notifications live in the view's
 /// ``Model``; the view itself only renders it and forwards the feature's output, the picker's changes, and the sheet's dismissal. All
-/// user-facing text is localized through the app's string catalog.
+/// user-facing text is localized through the app's string catalog, resolved via its generated string symbols.
 struct ContentView: View {
 
     // MARK: Properties
@@ -220,35 +220,6 @@ private enum Constant {
 
 // MARK: - Previews
 
-/// The preinstalling service used by the previews, which resolves every locale as supported and downloads nothing.
-private struct PreviewPreinstalling: Preinstalling {
-
-    /// The stream of events the service emits, which finishes immediately.
-    let events: AsyncStream<PreinstallingEvent> = .init { continuation in
-        continuation.finish()
-    }
-
-    func preinstall(
-        for locale: Locale
-    ) async {
-        // The previews preinstall no speech model assets.
-    }
-
-    func supportedLocale(
-        equivalentTo locale: Locale
-    ) async -> Locale? {
-        locale
-    }
-
-    func supportedLocales() async -> [Locale] {
-        [
-            Locale(identifier: "en-US"),
-            Locale(identifier: "nl-NL"),
-        ]
-    }
-
-}
-
 #Preview(
     "Content view"
 ) {

Apps/Attendi/Tests/Mocks/PreinstallingMock.swift

@@ -5,6 +5,8 @@ import Recording
 /// on demand.
 @MainActor
 final class PreinstallingMock: Preinstalling {
+    
+    // MARK: Properties
 
     /// The stream of events the service emits while preinstalling.
     let events: AsyncStream<PreinstallingEvent>
@@ -20,10 +22,14 @@ final class PreinstallingMock: Preinstalling {
 
     /// The continuation that feeds ``events``.
     private let continuation: AsyncStream<PreinstallingEvent>.Continuation
+    
+    // MARK: Initializers
 
     init() {
         (events, continuation) = AsyncStream.makeStream(of: PreinstallingEvent.self)
     }
+    
+    // MARK: Methods
 
     /// Emits the given event through ``events``.
     ///

Attendi.xcodeproj/project.pbxproj

@@ -34,6 +34,7 @@
 			membershipExceptions = (
 				Attendi/Catalogs/Assets.xcassets,
 				Attendi/Catalogs/Localizable.xcstrings,
+				Attendi/Previews/Services/PreviewPreinstalling.swift,
 				Attendi/Sources/App/AttendiApp.swift,
 				"Attendi/Sources/View Models/ContentViewModel.swift",
 				Attendi/Sources/Views/ContentView.swift,
@@ -285,6 +286,7 @@
 				COPY_PHASE_STRIP = NO;
 				CURRENT_PROJECT_VERSION = 1;
 				DEBUG_INFORMATION_FORMAT = dwarf;
+				DEVELOPMENT_ASSET_PATHS = Apps/Attendi/Previews/Services/PreviewPreinstalling.swift;
 				DEVELOPMENT_TEAM = 7FMNM89WKG;
 				ENABLE_APP_SANDBOX = YES;
 				ENABLE_HARDENED_RUNTIME = YES;
@@ -401,6 +403,7 @@
 				COPY_PHASE_STRIP = NO;
 				CURRENT_PROJECT_VERSION = 1;
 				DEBUG_INFORMATION_FORMAT = "dwarf-with-dsym";
+				DEVELOPMENT_ASSET_PATHS = Apps/Attendi/Previews/Services/PreviewPreinstalling.swift;
 				DEVELOPMENT_TEAM = 7FMNM89WKG;
 				ENABLE_APP_SANDBOX = YES;
 				ENABLE_HARDENED_RUNTIME = YES;