drawElementImage: pixel-perfect capture via html-in-canvas API using
<canvas layoutsubtree> with iframe child. Achieves 42 dB PSNR vs 30 dB
for SnapDOM. Requires Chrome --enable-blink-features=CanvasDrawElement.
Tab-capture: experimental getDisplayMedia-based capture.
Also adds regression parity scripts for compiling test compositions and
comparing PSNR against golden reference renders.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
