diff --git a/simulator/static/app.js b/simulator/static/app.js
index 86b0aff..52c9e62 100644
--- a/simulator/static/app.js
+++ b/simulator/static/app.js
@@ -136,7 +136,13 @@ async function preloadAllMedia(concurrency = 4) {
       const file = files[i++];
       if (!mediaBlobs[file]) {
         try {
-          const blob = await (await fetch(mediaUrl(file))).blob();
+          // `cache: "reload"` bypasses the browser HTTP cache and refetches from the
+          // network, then updates the cache entry. This busts a clip whose bytes were
+          // re-baked under the SAME path (e.g. a re-sourced cosmos base) — including
+          // one a pre-`no-cache` build had pinned `immutable, max-age=1y`, which a
+          // plain reload would never revalidate. The blob cache above still gives
+          // instant in-session swaps; this only affects the one fetch per (re)load.
+          const blob = await (await fetch("/media/" + file, { cache: "reload" })).blob();
           mediaBlobs[file] = URL.createObjectURL(blob);
         } catch (_) { /* leave it to the network path on demand */ }
       }