fix(ci): pin chrome-headless-shell + clamp PSNR checkpoint to a valid frame

Dockerfile.test

@@ -53,7 +53,12 @@ ENV CONTAINER=true
 # Install chrome-headless-shell for deterministic BeginFrame rendering.
 # This lightweight Chrome binary supports HeadlessExperimental.beginFrame.
 # Install to ~/.cache/puppeteer/ where resolveHeadlessShellPath() looks.
-RUN npx --yes @puppeteer/browsers install chrome-headless-shell@stable \
+#
+# Pinned to a specific build (NOT @stable) so the regression-test golden
+# baselines in packages/producer/tests/*/output/output.mp4 stay reproducible.
+# Each Chrome stable bump shifts pixel output enough to fail PSNR. Bump this
+# version together with regenerating baselines via `docker:test:update`.
+RUN npx --yes @puppeteer/browsers install chrome-headless-shell@148.0.7778.167 \
       --path /root/.cache/puppeteer \
     && find /root/.cache/puppeteer/chrome-headless-shell -name "chrome-headless-shell" -type f \
     && echo "chrome-headless-shell installed"

packages/producer/src/regression-harness.ts

@@ -1096,16 +1096,19 @@ async function runTestSuite(
         videoMetadata.durationSeconds,
         snapshotMetadata.durationSeconds,
       );
+      const fps = fpsToNumber(suite.meta.renderConfig.fps);
+      // Container duration includes audio padding past the last video frame
+      // (e.g. many-cuts: 5.654s container vs 5.6s of video). At i=99 the
+      // raw container duration maps to a frame index past nb_frames, and
+      // ffmpeg's PSNR filter emits no `average:` line for a non-existent
+      // frame. Subtract one frame interval so the last checkpoint always
+      // lands on a frame the video stream actually contains.
+      const sampleDuration = Math.max(0, videoDuration - 1 / fps);
 
       const minPsnrForMode = resolveMinPsnrForMode(options.mode, suite.meta.minPsnr);
       for (let i = 0; i < 100; i++) {
-        const time = (videoDuration * i) / 100;
-        const psnr = psnrAtCheckpoint(
-          renderedOutputPath,
-          snapshotVideoPath,
-          time,
-          fpsToNumber(suite.meta.renderConfig.fps),
-        );
+        const time = (sampleDuration * i) / 100;
+        const psnr = psnrAtCheckpoint(renderedOutputPath, snapshotVideoPath, time, fps);
         visualCheckpoints.push({
           time,
           psnr,