Coming back to the feed shows it as it was left

Leaving the feed keeps it in Services/FeedMemory.cs (posts, waiting posts, cursors and scroll; ten minutes, for the same
feed of the same persona), so coming back from a thread or a profile shows it again at once, older pages included,
instead of reading it anew; newer posts come behind the "new" button and through the stream as before.
tests/e2e FeedMemoryTests goes to a thread and back without a new read of the home timeline; the whole suite passes
(123, 5 skipped).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Pages/Index.razor

@@ -110,6 +110,7 @@
 	[Inject] StreamingService Streaming { get; set; }
 	[Inject] InstanceService InstanceService { get; set; }
 	[Inject] RequestStats RequestStats { get; set; }
+	[Inject] FeedMemory Memory { get; set; }
 
 	FeedFilter Filter { get; set; } = new();
 	List<FeedPost> posts = [];
@@ -129,6 +130,8 @@
 	FeedQuery lastQuery;
 	DateTime? lastPollAt;
 	TimeSpan? lastLoadTook;
+	// the scroll a recalled feed goes back to, once rendered
+	double? recalledScroll;
 
 	GlobePanel globe;
 	IJSObjectReference feedModule;
@@ -158,9 +161,36 @@
 			return;
 		}
 
+		if (await Recall())
+			return;
 		await Reload();
 	}
 
+	/// <summary>Shows the feed again as the reader left it, when it is the same feed of the same persona and recent.</summary>
+	async Task<bool> Recall()
+	{
+		if (!Memory.Holds(CascadingState.PersonaId))
+			return false;
+		groups = Memory.Groups;
+		lists = Memory.Lists;
+		if (Query != Memory.Query)
+			return false;
+
+		loadCancellation = new();
+		posts = Memory.Posts;
+		pending = Memory.Pending;
+		minId = Memory.MinId;
+		maxId = Memory.MaxId;
+		recalledScroll = Memory.ScrollTop;
+		loadedPersonaId = CascadingState.PersonaId;
+		lastQuery = Query;
+		IsLoading = false;
+		Memory.Forget();
+		await Streaming.Follow(StreamOf(Filter), loadCancellation.Token);
+		await ReadNotifications(loadCancellation.Token);
+		return true;
+	}
+
 	// The persona changed (NavMenu's switcher): everything on the page belongs to the old one.
 	protected override async Task OnParametersSetAsync()
 	{
@@ -177,6 +207,8 @@
 
 		reference = DotNetObjectReference.Create(this);
 		feedModule = await JS.InvokeAsync<IJSObjectReference>("import", "./js/feed.js");
+		if (recalledScroll is { } top)
+			await feedModule.InvokeVoidAsync("scrollToOffset", ScrollId, top);
 		await feedModule.InvokeVoidAsync("observeEnd", reference, SentinelId, ScrollId);
 		pollTimer = new(PollInterval);
 		_ = PollNewer(pageCancellation.Token);
@@ -511,6 +543,7 @@
 	public override async ValueTask DisposeAsync()
 	{
 		Streaming.Received -= OnStream;
+		await Remember();
 		await Streaming.Stop();
 		await pageCancellation.CancelAsync();
 		pageCancellation.Dispose();
@@ -531,6 +564,24 @@
 		await base.DisposeAsync();
 	}
 
+	/// <summary>Keeps the feed for the way back (FeedMemory), when it shows something worth keeping.</summary>
+	async Task Remember()
+	{
+		if (IsLoading || loadError is { Length: > 0 } || posts.Count == 0 || CascadingState.PersonaId is null
+			|| Filter.TimelineType is TimelineType.Nearby)
+			return;
+		var scrollTop = 0d;
+		try
+		{
+			if (feedModule is not null)
+				scrollTop = await feedModule.InvokeAsync<double>("scrollOffset", ScrollId);
+		}
+		catch (JSDisconnectedException)
+		{
+		}
+		Memory.Save(Query, posts, pending, groups, lists, minId, maxId, scrollTop);
+	}
+
 	sealed class GeoAnswer
 	{
 		public double? Latitude { get; set; }