revert: the player retry fix was based on a wrong root cause

_ensureVideo already registers the url on both the create and reuse paths, so
window-materialized elements always could retry; the added registration was a
no-op and its comment described a bug that does not exist.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -31,14 +31,6 @@
   quietly. Latent width and height snap to even, since a patchified model cannot take odd.
 
 ### Fixed
-- **Timeline playback died partway through a long timeline: play/pause left it on "Loading"
-  forever.** `_classifyVideoError` drops any element whose url is not registered in
-  `_urlClips`, and only `_syncPool` registered — which runs on a timeline rebuild, not as the
-  playhead moves. So every clip the sliding pool window materialized during playback could
-  never retry a failed load: one transient error (rapid play/pause over the network poisons a
-  stream) and that clip was stuck until a page reload. The boundary fell wherever the initial
-  window ended, which on a typical timeline is around the halfway point.
-
 - **A linked input driven by `Project · Prompt (global)` claimed to encode "the same text
   Studio would" and did not.** Studio appends the postfix to every scene itself, so the
   global prompt is strictly less than what it encodes — and the postfix is usually where

movie_editor/frontend/player.js

@@ -628,14 +628,7 @@
     for (const u of want) {
       if (pool.has(u)) continue;
       const clip = _clips.find((c) => _clipUrl(c) === u);
-      if (!clip) continue;
-      // Register BEFORE materializing: _classifyVideoError drops any element whose url is
-      // not in _urlClips, so an element created here without one could never retry a failed
-      // load and sat on "loading" forever. Only _syncPool registered, and it only runs on a
-      // timeline rebuild — so every clip the sliding window materialized during playback
-      // (i.e. everything past the first window) was unrecoverable.
-      _registerUrlClip(u, clip);
-      _ensureVideo(u, clip);
+      if (clip) _ensureVideo(u, clip);
     }
     if (pool.size <= POOL_MAX) return;
     for (const [u, v] of [...pool]) {  // Map order = insertion order ⇒ oldest first