Test-only approval commit after the f26ec7c main merge (sw-test-regression-
baseline section 9); no protected path changes, no Story change.
- approvedMainCommit 21fe7a2 -> f26ec7c.
- public-api.approved.json kept: the public .d.ts files are byte-identical.
- docs/sw/sw-viewer-header-strip-2026-10-21.md: changes and verification.
