Focus events on the live timeline when it has already loaded them

Opening a room on an event always built a detached timeline, even when the
live timeline already contained that event, e.g. when tapping the notification
for the newest message in a room.

The timeline controller now stays on the live timeline in that case, scrolling
to and highlighting the event, and only builds a detached timeline when the
event isn't loaded.

ElementX.xcodeproj/project.pbxproj

@@ -675,6 +675,7 @@
 		6A54F52443EC52AC5CD772C0 /* JoinRoomScreen.swift in Sources */ = {isa = PBXBuildFile; fileRef = 869A8A4632E511351BFE2EC4 /* JoinRoomScreen.swift */; };
 		6A5FDF9306CBD62C7EDDB552 /* CLLocationManagerMock.swift in Sources */ = {isa = PBXBuildFile; fileRef = C723327DC4A3093CD9675B27 /* CLLocationManagerMock.swift */; };
 		6A64546ABE648ED9E6DBB459 /* RemoteSettingsHook.swift in Sources */ = {isa = PBXBuildFile; fileRef = D5D186A6DB8FAC5C9D0E4D61 /* RemoteSettingsHook.swift */; };
+		6AA27078438185AEA8CDE2A1 /* TimelineControllerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = FE07EC9D34EF91795EDB3CC4 /* TimelineControllerTests.swift */; };
 		6AB306367E56A6F6DFA0E2FF /* RoomSummaryProviderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = F46E441BA50705E6CEC89FE0 /* RoomSummaryProviderTests.swift */; };
 		6AC798F52571BE495E6AA1CE /* OAuthAccountSettingsPresenter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 21819C86A022D6ADBA7A7A15 /* OAuthAccountSettingsPresenter.swift */; };
 		6AD722DD92E465E56D2885AB /* BugReportScreen.swift in Sources */ = {isa = PBXBuildFile; fileRef = BA919F521E9F0EE3638AFC85 /* BugReportScreen.swift */; };
@@ -3275,6 +3276,7 @@
 		FDB9C37196A4C79F24CE80C6 /* KeychainControllerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = KeychainControllerTests.swift; sourceTree = "<group>"; };
 		FDEDD4D2DE0646DA724985D5 /* QRCodeLoginScreenModels.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = QRCodeLoginScreenModels.swift; sourceTree = "<group>"; };
 		FDF73F49E6B6683F7E2D26F0 /* SecureBackupScreenCoordinator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SecureBackupScreenCoordinator.swift; sourceTree = "<group>"; };
+		FE07EC9D34EF91795EDB3CC4 /* TimelineControllerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TimelineControllerTests.swift; sourceTree = "<group>"; };
 		FE1E6FAA3719E9B7A2D5510B /* FormattingToolbar.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FormattingToolbar.swift; sourceTree = "<group>"; };
 		FE3AB4D399D39FBD78119011 /* AuthenticationStartScreenModels.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AuthenticationStartScreenModels.swift; sourceTree = "<group>"; };
 		FE5CD2993048222B64C45006 /* SDKListener.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SDKListener.swift; sourceTree = "<group>"; };
@@ -5343,6 +5345,7 @@
 				18B223FA339BF53085328DEE /* SpaceScreenViewModelTests.swift */,
 				6DF438EAFC732D2D95D34BF6 /* StartChatViewModelTests.swift */,
 				2CEBCB9676FCD1D0F13188DD /* StringTests.swift */,
+				FE07EC9D34EF91795EDB3CC4 /* TimelineControllerTests.swift */,
 				53C65A839BC897F6C236E8A5 /* TimelineInteractionHandlerTests.swift */,
 				9AA3AF94A06D319BB37E52DA /* TimelineItemFactoryTests.swift */,
 				C98C243A90369929D669873D /* TimelineItemMenuActionProviderTests.swift */,
@@ -8464,6 +8467,7 @@
 				6189B4ABD535CE526FA1107B /* StartChatViewModelTests.swift in Sources */,
 				1FEC0A4EC6E6DF693C16B32A /* StringTests.swift in Sources */,
 				E75CE800B3E64D0F7F8E228D /* TemplateScreenViewModelTests.swift in Sources */,
+				6AA27078438185AEA8CDE2A1 /* TimelineControllerTests.swift in Sources */,
 				ECE4E03D17E309724013F825 /* TimelineInteractionHandlerTests.swift in Sources */,
 				0D4EB2ABAA5FE8CB10FDBCB8 /* TimelineItemFactoryTests.swift in Sources */,
 				0668BECCF11E8EE6936CDF16 /* TimelineItemMenuActionProviderTests.swift in Sources */,

ElementX/Sources/Services/Timeline/TimelineController/TimelineController.swift

@@ -63,7 +63,8 @@ class TimelineController: TimelineControllerProtocol {
         activeTimeline = timelineProxy
         activeTimelineItemProvider = liveTimelineItemProvider
         
-        guard let initialFocussedEventID else {
+        // No need for a detached timeline when the live one has already loaded the event.
+        guard let initialFocussedEventID, !liveTimelineItemProvider.containsEvent(initialFocussedEventID) else {
             configureActiveTimelineItemProvider()
             return
         }
@@ -765,3 +766,12 @@ private nonisolated extension TimelineItemProxy {
         return false
     }
 }
+
+private extension TimelineItemProviderProtocol {
+    func containsEvent(_ eventID: String) -> Bool {
+        itemProxies.contains { item in
+            guard case let .event(eventItem) = item else { return false }
+            return eventItem.id.eventID == eventID
+        }
+    }
+}

UnitTests/Sources/TimelineControllerTests.swift

@@ -0,0 +1,72 @@
+//
+// Copyright 2026 Element Creations Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+// Please see LICENSE files in the repository root for full details.
+//
+
+import Combine
+@testable import ElementX
+import MatrixRustSDK
+import Testing
+
+@MainActor
+struct TimelineControllerTests {
+    private let roomProxy = JoinedRoomProxyMock(.init())
+    
+    @Test
+    func initialFocusOnLoadedEventUsesTheLiveTimeline() async throws {
+        let controller = makeController(liveEventIDs: ["$event"], initialFocussedEventID: "$event")
+        try await waitForTimelineItems(controller)
+        
+        #expect(!roomProxy.timelineFocusedOnEventEventIDNumberOfEventsCalled)
+        #expect(controller.timelineKind == .live)
+    }
+    
+    @Test
+    func initialFocusOnUnloadedEventLoadsADetachedTimeline() async throws {
+        let controller = makeController(liveEventIDs: ["$other"], initialFocussedEventID: "$event")
+        try await waitForTimelineItems(controller)
+        
+        #expect(roomProxy.timelineFocusedOnEventEventIDNumberOfEventsReceivedArguments?.eventID == "$event")
+    }
+    
+    // MARK: - Helpers
+    
+    private func makeController(liveEventIDs: [String], initialFocussedEventID: String) -> TimelineController {
+        let itemProxies = liveEventIDs.enumerated().map { index, eventID in
+            TimelineItemProxy.event(EventTimelineItemProxy(item: .init(configuration: .init(eventID: eventID)), uniqueID: .init("\(index)")))
+        }
+        let paginationState = TimelinePaginationState(backward: .idle, forward: .endReached)
+        
+        let provider = TimelineItemProviderMock()
+        provider.kind = .live
+        provider.itemProxies = itemProxies
+        provider.paginationState = paginationState
+        provider.membershipChangePublisher = PassthroughSubject().eraseToAnyPublisher()
+        provider.updatePublisher = CurrentValueSubject((itemProxies, paginationState)).eraseToAnyPublisher()
+        
+        roomProxy.timelineFocusedOnEventEventIDNumberOfEventsReturnValue = .failure(.eventNotFound)
+        
+        return TimelineController(roomProxy: roomProxy,
+                                  timelineProxy: TimelineProxyMock(.init(timelineItemProvider: provider)),
+                                  initialFocussedEventID: initialFocussedEventID,
+                                  timelineItemFactory: RoomTimelineItemFactory(userID: "@alice:matrix.org",
+                                                                               attributedStringBuilder: AttributedStringBuilder(mentionBuilder: MentionBuilder()),
+                                                                               stateEventStringBuilder: RoomStateEventStringBuilder(userID: "@alice:matrix.org")),
+                                  mediaProvider: MediaProviderMock(.init()),
+                                  userSettings: .volatile())
+    }
+    
+    /// The live timeline's items are only published once any initial focus attempt has finished.
+    private func waitForTimelineItems(_ controller: TimelineController) async throws {
+        let deferred = deferFulfillment(controller.callbacks) { callback in
+            if case .updatedTimelineItems = callback {
+                true
+            } else {
+                false
+            }
+        }
+        try await deferred.fulfill()
+    }
+}