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

wwwroot/js/feed.js

@@ -34,6 +34,17 @@ export function isVisible() {
 	return document.visibilityState === "visible"
 }
 
+// The scroll a feed was left at, and the way back to it (Services/FeedMemory.cs).
+export function scrollOffset(rootId) {
+	return document.getElementById(rootId)?.scrollTop ?? 0
+}
+
+export function scrollToOffset(rootId, top) {
+	const root = document.getElementById(rootId)
+	if (root)
+		root.scrollTop = top
+}
+
 export function scrollToTop(rootId) {
 	document.getElementById(rootId)?.scrollTo({ top: 0, behavior: matchMedia("(prefers-reduced-motion: reduce)").matches ? "auto" : "smooth" })
 }