fix(ci): pin Lighthouse Chromium and stop advisory Chrome-drift fails

[BigSimmo]

Summary

• Diagnose PR fix(navigation): wire the forms section anchors, drop the dead presentation set #1697 advisory failure: Lighthouse budget (advisory) exited 1 with Evidence incomplete because the committed baseline was measured on HeadlessChrome/151 while that job measured on HeadlessChrome/150. Metrics were fine; required PR required was already green and the PR had merged.
• Pin Chromium for the pre-merge Lighthouse job through Playwright (setup-ui-e2e + CHROME_PATH) so the browser only moves with the lockfile, not the ubuntu image Chrome rollout.
• While enforce is still false, treat baseline browser mismatch as a warning (exit 0) instead of a hard fail; once enforce flips, mismatch still fails closed until --update.
• Fix the --update catch-22: baseline-comparability checks (Chrome drift / missing rows) no longer block a refresh that exists to rewrite them.

Verification

• Reproduced PR fix(navigation): wire the forms section anchors, drop the dead presentation set #1697 artifact grade: same Chrome 151 vs 150 mismatch now exits 0 with ::warning::check:lighthouse-budget — baseline browser mismatch — refresh with --update
• Proved --update --dir <artifact> succeeds (exit 0) against that Chrome-drift evidence, then restored lighthouse-budget.json (did not commit system-Chrome 150 numbers; CI will restamp on pinned Playwright Chromium)
• Direct Node contract assertions for warn/fail/update-skip/CI pin/table label: PASS
• Verification not run: full npm run test / verify:pr-local — shared node_modules junction was mid-mutation and the repo heavy-run lock was held by another worktree; CI will run the lighthouse unit suite and workflow contracts on this head

Risk and rollout

• Risk: Advisory Lighthouse may warn (not fail) on browser mismatch until the baseline is restamped on the pinned Playwright Chromium after this lands. Once enforce is true, mismatch still fails.
• Rollback: Revert this commit; advisory job returns to system Chrome and hard-fail on major drift.
• Provider or production effects: None

Notes

• Does not change product UI or retrieval behaviour.
• Follow-up for #118: after this merges, download a green lighthouse artifact measured with the pinned Chromium and run npm run check:lighthouse-budget -- --update before flipping enforce.

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📥 Commits

Reviewing files that changed from the base of the PR and between cbca371 and 6211808.

📒 Files selected for processing (26)

• .github/workflows/ci.yml
• docs/branch-review-ledger.md
• docs/design-system/COMPONENTS.md
• docs/design-system/adoption-manifest.json
• docs/outstanding-issues.md
• docs/search-chrome-behaviour.md
• docs/search-results-bar-decisions.md
• docs/testing.md
• scripts/check-lighthouse-budget.mjs
• src/components/applications-launcher-page.tsx
• src/components/clinical-dashboard/differentials-home.tsx
• src/components/clinical-dashboard/medication-prescribing-workspace.tsx
• src/components/clinical-dashboard/result-filter-control.tsx
• src/components/clinical-dashboard/search-results-header-band.tsx
• src/components/factsheets/factsheets-search-page.tsx
• src/components/formulation/formulation-home-page.tsx
• src/components/services/services-navigator-page.tsx
• src/components/specifiers/specifiers-home-page.tsx
• tests/check-lighthouse-budget.test.ts
• tests/search-results-header-band.dom.test.tsx
• tests/ui-accessibility.spec.ts
• tests/ui-formulation.spec.ts
• tests/ui-smoke.spec.ts
• tests/ui-specifiers.spec.ts
• tests/ui-stress.spec.ts
• tests/ui-tools.spec.ts

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[BigSimmo]

Superseded by #1716, which merged the same fix (pin Playwright's managed Chromium for the lighthouse-budget job instead of relying on the ambient ubuntu-24.04 runner Chrome). #1716 was a minimal, workflow-only change — it doesn't modify check-lighthouse-budget.mjs's fail-closed grading contract the way this PR does — and was live-validated on a manual workflow_dispatch run before merge (Lighthouse budget (advisory) went from consistent failure to success).

Closing this to avoid duplicate/conflicting work on the same job. Thanks for the diagnosis work here — the root-cause analysis (Chrome 150/151 drift across the runner fleet) matches what landed.

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