Start a foreground search backfill request when entering the message search tab

ElementX/Sources/Screens/SearchScreen/SearchScreenViewModel.swift

@@ -102,8 +102,12 @@ class SearchScreenViewModel: SearchScreenViewModelType, SearchScreenViewModelPro
         // Re-run the search when switching tabs so the newly active tab reflects the current query.
         let searchModeStream = context.observe(\.viewState.bindings.searchMode).removeDuplicates()
         searchModeObservationTask = Task { [weak self] in
-            for await _ in searchModeStream {
+            for await searchMode in searchModeStream {
                 guard let self else { return }
+                // Opening the messages tab signals the user actually wants history to be searchable.
+                if searchMode == .messages {
+                    clientProxy.startSearchBackfill(strategy: .foreground)
+                }
                 updateFilter(for: state.bindings.searchQuery)
             }
         }

UnitTests/Sources/SearchScreenViewModelTests.swift

@@ -21,6 +21,8 @@ struct SearchScreenViewModelTests {
     let setQuerySubject = PassthroughSubject<String, Never>()
     /// Fires each time an indicator is submitted.
     let submitIndicatorSubject = PassthroughSubject<Void, Never>()
+    /// Fires each time a search backfill is started, with whether it used the foreground strategy.
+    let startSearchBackfillSubject = PassthroughSubject<Bool, Never>()
     
     var context: SearchScreenViewModelType.Context {
         viewModel.context
@@ -42,6 +44,9 @@ struct SearchScreenViewModelTests {
         
         let clientProxy = ClientProxyMock(.init())
         clientProxy.searchService = searchService
+        clientProxy.startSearchBackfillStrategyClosure = { [startSearchBackfillSubject] strategy in
+            startSearchBackfillSubject.send(strategy == .foreground)
+        }
         let staticRoomSummaryProvider = RoomSummaryProviderMock()
         staticRoomSummaryProvider.roomListPublisher = staticRoomListSubject.asCurrentValuePublisher()
         clientProxy.staticRoomSummaryProvider = staticRoomSummaryProvider
@@ -97,6 +102,13 @@ struct SearchScreenViewModelTests {
         #expect(searchService.setQueryReceivedQuery == "Foundation")
     }
     
+    @Test
+    func openingMessagesTabStartsSearchBackfill() async throws {
+        let deferred = deferFulfillment(startSearchBackfillSubject) { $0 }
+        context.searchMode = .messages
+        try await deferred.fulfill()
+    }
+    
     @Test
     func messageSearchFailureShowsErrorIndicator() async throws {
         searchService.setQueryClosure = { _ in .failure(.sdkError(SearchScreenViewModelTestsError.failed)) }