_🎯 Functional Correctness_ | _🟡 Minor_ | _⚡ Quick win_

[BigSimmo]

🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Require and document complete uniform browser drift before aggregation.

The aggregation must only apply when every expected run has the same browser-version drift and no other evidence problem exists.

• scripts/check-lighthouse-budget.mjs#L130-L151: require drift to contain every expected run before returning the collapsed message. Add a regression test for a version-less legacy baseline row.
• docs/testing.md#L150-L152: state that mixed, partial, or otherwise incomplete evidence retains per-run diagnostics.

📍 Affects 2 files

• scripts/check-lighthouse-budget.mjs#L130-L151 (this comment)
• docs/testing.md#L150-L152

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@scripts/check-lighthouse-budget.mjs` around lines 130 - 151, The
browser-drift aggregation in the budget comparison flow must require drift
coverage for every expected run, in addition to a single drift pair and no
measurement problems; otherwise retain per-run diagnostics. Add a regression
test covering a version-less legacy baseline row. Update docs/testing.md lines
150-152 to document that mixed, partial, or incomplete evidence remains reported
per run.

Originally posted by @coderabbitai[bot] in #1722 (comment)

[coderabbitai]

🔗 Related PRs

#705 - test: harden reliable test execution [merged]
#841 - fix: resolve design-audit and CI regression guard blockers [open]
#1279 - test: harden phone chrome verification and merge safeguards [merged]
#1432 - fix: Playwright browser preflight prevents #120 false greens [merged]
#1722 - ci(lighthouse): make the budget gate self-healing and scope it to perf-relevant diffs [open]

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