Venues: song sky, ride roadside, room camera, filmstrip venue pin

- Shared sky dome (src/venues/sky.js): gradient backdrop from palette /
  section light / style texture, wired into chamber/stage/ride with fog
  matched to the dome mid colour — replaces clear-to-black
- Ride roadside: houses, signs, trees, seeded viz billboard, all analytic
  scroll; popMul fade for crew, arrangement-gated roadside (no mid-section
  popping); parked idle creep + engine shake; analytic dash clock
- Room camera: traverse glide + progress look sweep + per-section dolly,
  single-side room visits, one re-hang max; venue framing per archetype
- Filmstrip venue selector (?venueSel=) with cache key; seed persisted to
  URL on reroll; gallery query plumbing

flow-state/src/main.js

@@ -291,9 +291,26 @@ document.addEventListener('keydown', (e) => {
 
 // ---------------------------------------------------------------- look edits
 
+/**
+ * Persist the current look seed into the URL so a reload restores it.
+ *
+ * Only meaningful with `?song=` (bank songs load by name; a dropped file has
+ * no URL identity, so a seed alone restores nothing). Uses replaceState — no
+ * reload, no history spam.
+ */
+function persistSeedInUrl() {
+    try {
+        const q = new URLSearchParams(location.search);
+        if (!q.get('song')) return;
+        q.set('seed', String(state.show.look.seed >>> 0));
+        history.replaceState(null, '', `${location.pathname}?${q}`);
+    } catch { /* non-browser or sandboxed iframe — seeding still works in-memory */ }
+}
+
 document.getElementById('btn-reroll').addEventListener('click', () => {
     if (!state.show.ready) return;
     state.show.reroll((state.show.look.seed ^ (++state.rerollSalt * 0x9e3779b9)) >>> 0);
+    persistSeedInUrl();
     refreshAfterLookChange();
 });