fix(home): shelf honours the Plex gate; hero unpins its origin; palette asks for a surprise

- A13: with Plex off, the Home shelf and the hero's comfort tier go YouTube-only like the rails
  beside them (owner's call: hide the tiles). The pins are kept; GET /pins still lists them.
- Reorder deals the listed pins into the slots they already hold, so a partial list (hidden Plex
  pins, a stale tab) no longer puts two pins on one position; repeats are ignored.
- A21: a comfort hero carries `pinned_from`, the shelf entry it was resolved from; its menu acts on
  that pin, so a pinned show's next episode offers "Unpin" instead of creating a second pin.
- B12: the palette's "Meglepetés" asks for the surprise tier (the next press leading with it); the
  rotation carries on from there.
- B13: the surprise token names the history entry it was requested for (minted by setPage's new
  `then`, after the push) and is dropped on any other entry, so a navigation that never mounted
  Home cannot replay it later.

frontend/src/lib/homeIntent.ts

@@ -1,3 +1,4 @@
+import { ensureNavId, peekNavId } from "./history";
 import { createStore } from "./store";
 
 // A one-shot "…and surprise me straight away" request for the Home surface (E24), handed over by
@@ -5,18 +6,23 @@ import { createStore } from "./store";
 //
 // A TOKEN that waits, not an event that fires: Home is a lazy module and is normally NOT mounted
 // when the request is made (the palette navigates to it in the same click), so an event would be
-// shouted into an empty room. Home takes the token on arrival, which clears it, so walking back to
-// Home an hour later does not replay the press — a stale reroll would look like the page deciding
-// on its own that the answer you came back for was wrong.
-const surprise = createStore(0);
+// shouted into an empty room. Home takes the token on arrival, which clears it.
+//
+// The token is the HISTORY ENTRY it was requested for, and Home honours it only on that entry. A
+// plain counter outlived a navigation that never mounted Home — a lazy chunk that failed, a Back
+// before the module arrived — and replayed on the next visit, an hour later: the page deciding on
+// its own that the answer you came back for was wrong. So it is minted AFTER the push
+// (`setPage`'s `then`), on the entry the push made; Home mounting on any other entry drops it.
+const surprise = createStore<number | null>(null);
 
-/** Ask Home to reroll its hero as soon as it is on screen. Pair it with a `setPage("home")`. */
-export const requestSurprise = (): void => surprise.set((n) => n + 1);
+/** Ask Home to reroll its hero on THIS history entry. Call it once the navigation to Home has
+ *  pushed — `setPage("home", requestSurprise)` — so the token names Home's own entry. */
+export const requestSurprise = (): void => surprise.set(ensureNavId());
 
-/** The pending token (0 = nothing pending) — the render subscription that wakes Home up. Home only. */
-export const useSurpriseRequest = (): number => surprise.use();
+/** The pending token (null = nothing pending) — the render subscription that wakes Home up. Home only. */
+export const useSurpriseRequest = (): number | null => surprise.use();
 
-/** Take the pending request, clearing it; false when there was nothing to take.
+/** Take the pending request, clearing it; true only when it was requested for the entry Home is on.
  *
  *  Compare-and-clear rather than a plain read + `consume()`, because a reroll is NOT idempotent — it
  *  spends a `/discover/pick` and steps the tier rotation — and React 18's StrictMode invokes a mount
@@ -24,7 +30,8 @@ export const useSurpriseRequest = (): number => surprise.use();
  *  "Meglepetés" from another module arrived at Home as `start=2`, two picks deep, before the page had
  *  painted once. Checking the LIVE store is what makes the second pass a no-op. */
 export const takeSurprise = (): boolean => {
-  if (!surprise.get()) return false;
-  surprise.set(0);
-  return true;
+  const entry = surprise.get();
+  if (entry === null) return false;
+  surprise.set(null);
+  return entry === peekNavId();
 };