fix(core): a smaller preview copy nobody wants any more no longer swaps in (#6973)

* fix(core): a smaller preview copy nobody wants any more no longer swaps in

* refactor(core): name the dropped copy instead of commenting it

packages/core/src/runtime/mediaProxy.test.ts

@@ -1025,6 +1025,40 @@ describe("preview quality: lighter copies of heavy files", () => {
     delete (window as { __HF_MEDIA_SOURCE_FACTS__?: unknown }).__HF_MEDIA_SOURCE_FACTS__;
   });
 
+  it("drops a smaller copy still being made when the level goes back up, so it never swaps in", async () => {
+    vi.useFakeTimers();
+    let lowerMade = false;
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async (url: string) =>
+        lowerMade || !String(url).includes("hf-proxy-box=1024")
+          ? new Response("x", { status: 206 })
+          : new Response(null, { status: 202, headers: { "Retry-After": "2" } }),
+      ),
+    );
+    const { video, setPreviewQuality, maybeProxyProactively } = await stage(
+      { "/video.mp4": HEAVY },
+      { "/video.mp4": HEVC_ENTRY },
+    );
+    const { copiesReady } = await import("./previewCopies");
+    const el = video();
+    stubCanPlayType(el, "");
+    maybeProxyProactively(el);
+    await vi.advanceTimersByTimeAsync(0);
+    expect(params(el).get("hf-proxy-box")).toBe("2048x1218");
+    expect(el.load).toHaveBeenCalledTimes(1);
+
+    setPreviewQuality(0.5);
+    await vi.advanceTimersByTimeAsync(0);
+    setPreviewQuality(1);
+    lowerMade = true;
+    await vi.advanceTimersByTimeAsync(60_000);
+
+    expect(params(el).get("hf-proxy-box")).toBe("2048x1218");
+    expect(el.load).toHaveBeenCalledTimes(1);
+    expect(copiesReady()).toBe(true);
+  });
+
   it("changes nothing at full quality", async () => {
     const { video, setPreviewQuality, maybeProxyProactively } = await stage({
       "/video.mp4": HEAVY,

packages/core/src/runtime/mediaProxy.ts

@@ -156,10 +156,14 @@ function keepSized(el: HTMLMediaElement, scale: number): void {
   if (needed && lowered && copy.light && lightCopyNoLongerNeeded(el, needed)) {
     return restoreOriginal(el);
   }
-  if (boxCovers(copy.box, needed, lowered)) return;
+  if (boxCovers(copy.box, needed, lowered)) return dropUnneededCopy(el);
   requestBox(el, copy, lowered || !needed ? needed : growOnly(needed, copy.box));
 }
 
+function dropUnneededCopy(el: HTMLMediaElement): void {
+  if (pendingUpgrades.delete(el)) noteCopy(el, "ready");
+}
+
 function lightCopyNoLongerNeeded(el: HTMLMediaElement, needed: PreviewProxyBox): boolean {
   const facts = sourceFactsOf(el);
   return facts !== null && !isHeavyForPreview(facts, needed);
@@ -193,7 +197,7 @@ function requestBox(el: HTMLMediaElement, copy: BoxedCopy, box: PreviewProxyBox
   void waitForServedProxy(
     href,
     wanted,
-    (fraction) => noteCopy(el, "making", fraction),
+    (fraction) => wanted() && noteCopy(el, "making", fraction),
     () => isActiveAtPlayhead(el),
   ).then((served) => {
     if (wanted()) noteCopy(el, served ? "ready" : "failed");