v3: src/ gets one layout rule and keeps to it — each layer holds one kind of module, and every layer is split into the same domains — the previous pass sorted components into folders but left hooks, helpers and a barrel inside them, kept hooks/, utils/ and contexts/ flat, and still grouped most tests by theme. The rule: components/ holds only components (.tsx), contexts/ holds FooContext.ts + FooProvider.tsx pairs, hooks/ every hook, utils/ every non-React module, pages/ one component per route and nothing else. Each of components/, contexts/, hooks/ and utils/ is split into the same domains — auth, category, chat, comment, dump, editor, feed, form, layout, player, playlist, profile, social, theme, ws — plus shared/ for what belongs to no one domain, so the chat is components/chat, contexts/chat, hooks/chat and utils/chat. components/ui becomes components/shared to match. Out of components/: useApiForm goes to hooks/form, chat's message.ts and time.ts to utils/chat (with chatDraft and chatText, now draft.ts and text.ts), the emoji skin tone to utils/editor, the remembered volume to utils/player; player/icons.tsx is PlayerIcons.tsx. components/form/index.ts is gone: everything is imported from its own file, FormProvider straight from react-hook-form, and expectOk sits beside friendlyFetchError in utils/shared/api.ts (apiError.ts), since pages that have no form used it too. Out of pages/: the index's feed views, tab bar and presence row move to components/feed; HotFeed and NewFeed, identical but for the sort, are one DumpFeed with an order prop, which also takes over MainFeedProps from pages/index/types.ts. App is a named export like everything else. Tests mirror the tree one file per module — test/<layer>/<domain>/<Module>.test.tsx — so the themed files (hooks/misc, data, editor, sync; utils/misc, text, storage, remote, journal; contexts/providers; pages/auth and UserSubpages; layout/Fabs) are split by subject, the setup each piece needs kept and the rest dropped; the floating-button test becomes one test per button, 627 tests now. The README states the rule. No behaviour changes; the catalogues only move their source references.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/hooks/feed/useScrollSave.ts

@@ -0,0 +1,37 @@
+import { useEffect, useLayoutEffect, useRef } from "react";
+
+/**
+ * Calls `onSave(scrollY)` when the page is left — the component unmounts (a
+ * navigation within the app) or the tab goes away (`pagehide`) — as long as
+ * `enabled` is true (e.g. the page is loaded).
+ *
+ * Scrolling itself only notes the position: saving serializes the whole feed
+ * into sessionStorage, which on every pause in scrolling cost a long task.
+ */
+export function useScrollSave(
+  enabled: boolean,
+  onSave: (scrollY: number) => void,
+) {
+  const onSaveRef = useRef(onSave);
+  useLayoutEffect(() => {
+    onSaveRef.current = onSave;
+  });
+
+  useEffect(() => {
+    if (!enabled) return;
+    // Tracked as it happens: by the time the unmount runs, the next page may
+    // already have scrolled the window back to the top.
+    let y = globalThis.scrollY;
+    const onScroll = () => {
+      y = globalThis.scrollY;
+    };
+    const save = () => onSaveRef.current(y);
+    globalThis.addEventListener("scroll", onScroll, { passive: true });
+    globalThis.addEventListener("pagehide", save);
+    return () => {
+      globalThis.removeEventListener("scroll", onScroll);
+      globalThis.removeEventListener("pagehide", save);
+      save();
+    };
+  }, [enabled]);
+}