Bind validation report to fallback sources

tests/golden/WBV2/full-source-parity-validation-report.json

@@ -1,8 +1,8 @@
 {
   "schemaVersion": 1,
   "reportId": "WBV2-FULL-SOURCE-PARITY-VALIDATION-001",
-  "generatedAt": "2026-09-07T09:10:38.474Z",
-  "gitCommit": "f68c6c9678d67641d14ea6b17b53c0cfa24adb51",
+  "generatedAt": "2026-09-07T09:19:37.040Z",
+  "gitCommit": "93c01c8f09e734f69a41451394d443ebbece2233",
   "sourceParityStatus": "PARTIAL",
   "webProductStatus": "READY",
   "releaseStatus": "READY",

web/app/src/sequencer/SequencerCodecProbe.ts

@@ -129,6 +129,19 @@ export async function probeSequencerCodec(
   return probeMovie(request, source);
 }
 
+/** Probe a movie with the browser decoder first, then use the local ffmpeg.wasm
+ * Worker when Chromium cannot decode the container/codec. */
+export async function probeSequencerMovieCodecWithFallback(
+  requestValue: unknown,
+  source: ArrayBuffer,
+  signal?: AbortSignal,
+): Promise<SequencerCodecProbeResultIR> {
+  const browserResult = await probeSequencerCodec(requestValue, source);
+  if (browserResult.status === "READY") return browserResult;
+  const { probeMovieWithFFmpeg } = await import("./FFmpegMovieProbe");
+  return probeMovieWithFFmpeg(requestValue, source, signal);
+}
+
 export function createSequencerCodecProbeRequest(
   stripType: SequencerCodecProbeRequestIR["stripType"],
   mimeType: string,

web/app/src/sequencer/SequencerMediaProxyCache.ts

@@ -88,6 +88,21 @@ export async function generateInitialSequencerMovieProxyFrame(
     throw new SequencerMediaCacheValidationError("SEQUENCER_CACHE_SOURCE_MISMATCH", "Movie proxy source bytes failed identity verification");
   }
   cancelled(signal);
+  if (capability.backend === "FFMPEG_WASM") {
+    try {
+      const { decodeMovieFrameWithFFmpeg } = await import("./FFmpegMovieProbe");
+      const frame = await decodeMovieFrameWithFFmpeg(source, sourceData, profile.width, profile.height, signal);
+      cancelled(signal);
+      return {
+        manifest: await createSequencerMediaCacheManifest(source, capability, profile, 0, frame.rgba),
+        data: frame.rgba,
+      };
+    }
+    catch (error) {
+      if (error instanceof DOMException && error.name === "AbortError") throw new SequencerMediaCacheValidationError("SEQUENCER_CANCELLED", "Movie proxy generation was cancelled");
+      throw new SequencerMediaCacheValidationError("SEQUENCER_CODEC_UNSUPPORTED", "ffmpeg.wasm movie proxy frame decode failed");
+    }
+  }
   if (typeof document === "undefined" || typeof HTMLMediaElement === "undefined") {
     throw new SequencerMediaCacheValidationError("SEQUENCER_CODEC_UNSUPPORTED", "HTML media proxy generation is unavailable");
   }