frontend/src/exportVideo.js fills the foundation2 stub: the ⏺ button
records the scene3d canvas captureStream(30) muxed with the live WebAudio
mix via the transport.captureAudioStream() hook (spatial included, silent
tap when no track — degrade, don't block), MediaRecorder vp9/opus webm
(vp8/webm fallbacks), spanning first -> last camPath keyframe. Playback is
driven through the existing #btn-path flow at forced rate 1 (file duration
must equal the path span), stops at the last keyframe (or early on a
second click / anything that halts the ride), downloads
festival4d-cut.webm, then restores ALL prior transport/UI state (playhead,
rate, play state, path state, followed camera) and releases the audio tap
+ canvas tracks. Button disabled under 2 keyframes by chaining main.js's
camPath.onChange (frozen files untouched).
Requires live-browser verification (focused tab — captureStream delivers
no frames hidden): see plan/status/lane-E.md. Frontend build clean.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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