Decide on cross-browser screenshot baseline storage

[PAMulligan]

Problem

Phase 7 (Cross-Browser) takes Firefox/WebKit screenshots but baselines aren't checked into the repo. Without baselines, the phase has nothing to diff against and effectively only verifies that rendering didn't throw.

Options

• Commit baselines to the repo (large diffs, easy to inspect)
• Use Git LFS
• Store baselines as CI artifacts and only compare against last green main
• Use a third-party visual diffing service (Chromatic, Percy)

Acceptance criteria

• Decision documented in docs/rfcs/
• Implementation tracked as a follow-up issue

Milestone

v2.0.0