Address PR review comments

- Extract activateCurrentSession() helper so start() and activateSession(for:) share one path
- Add @mainactor doc comment to ServiceLocatorProvider explaining the isolation requirement
- Add MARK comment to SessionProvider extension clarifying ServiceLocatorProvider conformance
- Add comment in SceneDelegate explaining why @service can't be used for the dark mode subscription
- Rename test variable login → loginSession for clarity

Co-authored-by: Charles Wang <g-enius@users.noreply.github.com>

Author: github-actions[bot]

Coordinator/Sources/Coordinator/AppCoordinator.swift

@@ -55,8 +55,7 @@ public final class AppCoordinator: BaseCoordinator, SessionProvider {
     // MARK: - Start
 
     override public func start() {
-        session.activate()
-        onSessionActivated?()
+        activateCurrentSession()
         switch currentFlow {
         case .login:
             showLoginFlow(session: session)
@@ -67,13 +66,16 @@ public final class AppCoordinator: BaseCoordinator, SessionProvider {
 
     // MARK: - Session Lifecycle
 
+    private func activateCurrentSession() {
+        session.activate()
+        onSessionActivated?()
+    }
+
     private func activateSession(for flow: AppFlow) -> Session {
         session.teardown()
-        let newSession = sessionFactory.makeSession(for: flow)
-        newSession.activate()
-        session = newSession
-        onSessionActivated?()
-        return newSession
+        session = sessionFactory.makeSession(for: flow)
+        activateCurrentSession()
+        return session
     }
 
     // MARK: - Flow Management

Core/Sources/Core/ServiceLocator.swift

@@ -62,6 +62,9 @@ public class ServiceLocator {
 // MARK: - ServiceLocatorProvider
 
 /// Any type that holds a ServiceLocator instance for instance-based DI resolution.
+///
+/// `@MainActor` is required because `ServiceLocator` itself is `@MainActor` —
+/// any property that returns a `ServiceLocator` must also be isolated to the main actor.
 @MainActor
 public protocol ServiceLocatorProvider {
     var serviceLocator: ServiceLocator { get }
@@ -76,6 +79,8 @@ public protocol SessionProvider: ServiceLocatorProvider {
     var session: Session { get }
 }
 
+// MARK: - ServiceLocatorProvider
+
 extension SessionProvider {
     public var serviceLocator: ServiceLocator { session.serviceLocator }
 }

FunApp/FunApp/SceneDelegate.swift

@@ -65,6 +65,9 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
 
     private func subscribeToDarkMode() {
         guard let session = appCoordinator?.session else { return }
+        // @Service can't be used here: SceneDelegate is not a ServiceLocatorProvider,
+        // and the session (and its locator) changes on each transition — we must
+        // re-resolve from the current session's locator on every activation.
         let toggles: FeatureToggleServiceProtocol = session.serviceLocator.resolve(for: .featureToggles)
         darkModeCancellable?.cancel()
         darkModeCancellable = toggles.appearanceModePublisher

Services/Tests/ServicesTests/SessionTests.swift

@@ -85,14 +85,14 @@ struct SessionTests {
             #expect(main.serviceLocator.isRegistered(for: .favorites))
 
             main.teardown()
-            let login = LoginSession()
-            login.activate()
+            let loginSession = LoginSession()
+            loginSession.activate()
 
             // Login session has only its own services — no stale favorites
-            #expect(login.serviceLocator.isRegistered(for: .logger))
-            #expect(login.serviceLocator.isRegistered(for: .network))
-            #expect(login.serviceLocator.isRegistered(for: .featureToggles))
-            #expect(!login.serviceLocator.isRegistered(for: .favorites))
+            #expect(loginSession.serviceLocator.isRegistered(for: .logger))
+            #expect(loginSession.serviceLocator.isRegistered(for: .network))
+            #expect(loginSession.serviceLocator.isRegistered(for: .featureToggles))
+            #expect(!loginSession.serviceLocator.isRegistered(for: .favorites))
         }
 
         @Test("Favorites are fresh after session transition")