fix(inspect): reset a released preview video in the next task

On WebKit (GStreamer) a video replaced while its pipeline was still
starting blocked the page: pause, src removal and load() in one task
never returned, so the next chooser selection hung (CI page workflows
webkit shard 2/2, "URLs and media end with their owning session").
The src is still dropped before the URL is revoked; only the load()
reset moves to the next task. A fresh-page regression replaces the
first video as soon as it shows, fifteen times.

TESTING.md

@@ -1296,8 +1296,10 @@ mapped differences"):
   `image/png,image/jpeg,image/webp` plus `video/*,.mp4,.mov,.m4v,.webm,.mkv,.avi,.wmv`. A
   video previews in the same `#local-preview` slot as `video.local-file-preview` with
   native `controls`, `playsInline`, `preload="metadata"` and `muted`, never autoplays
-  inline, and is paused, unloaded (`removeAttribute('src')`, `load()`) and removed on
+  inline, and is paused, has its `src` removed and is removed from the page on replacement
-  replacement or dispose.
+  or dispose, before its URL is revoked; its `load()` reset runs in the next task, because
+  WebKit (GStreamer) blocked the page when a still-starting video was reset in the same
+  task (`replacing a video that just started loading never blocks the page`).
 - **D63** (status line): one `p.small.spaced-16` in `#local-preview`, for states the
   concept never shows: "Drop one file at a time.", "Folders cannot be inspected. Choose
   one image or video file.", "This file type cannot be previewed or inspected here.

tests/browser/workspace-inspect.spec.mjs

@@ -391,6 +391,28 @@ test('URLs and media end with their owning session', async ({ page }) => {
     expect(state.revoked.filter(url => url === state.created[7])).toHaveLength(1);
 });
 
+test('replacing a video that just started loading never blocks the page', async ({ context, browserName }) => {
+    test.setTimeout(120000);
+    // WebKit (GStreamer) blocked the page when a video's pipeline was reset with load() in the same task that
+    // removed its src, while it was still starting: the next chooser selection never completed. Each fresh page
+    // replaces its first video as soon as it shows.
+    for (let attempt = 0; attempt < 15; attempt++) {
+        const page = await context.newPage();
+        try {
+            if (attempt === 0) await startCoverage(page, browserName);
+            await openInspect(page);
+            await choose(page, localFixture('core-tags.webm', 'video/webm'));
+            await expect(preview(page).locator('video.local-file-preview')).toBeVisible();
+            await chooser(page).setInputFiles(parityPng('f02.png'), { timeout: 8000 });
+            await expect(preview(page).locator('img.local-file-preview')).toBeVisible();
+            await expect(preview(page).locator('video')).toHaveCount(0);
+            if (attempt === 0) await saveCoverage(page, browserName);
+        } finally {
+            await page.close();
+        }
+    }
+});
+
 test('replacing a file mid-read never shows or sends the old record', async ({ page, context }) => {
     const host = await bridgeHost(context);
     try {

web/js/workspace/inspect.mjs

@@ -37,10 +37,14 @@ function element(tag, className, text) {
     return node;
 }
 
-/** Stops a preview from holding its blob: URL: media is paused and unloaded before the session revokes the URL. */
+/**
+ * Stops a preview from holding its blob: URL: media is paused and its src dropped before the session revokes the URL.
+ * The media resets with load() in the next task: WebKit (GStreamer) blocked the page when a starting video was reset in
+ * the same task that removed its src.
+ */
 function releaseMedia(node) {
     if (!node) return;
-    if (node instanceof HTMLMediaElement) { node.pause(); node.removeAttribute('src'); node.load(); }
+    if (node instanceof HTMLMediaElement) { node.pause(); node.removeAttribute('src'); setTimeout(() => node.load(), 0); }
     else node.removeAttribute('src');
     node.remove();
 }