docs(sw): document storybook regression baseline maintenance

packages/sw/tests/storybook-inventory.mjs

@@ -40,6 +40,17 @@ export const integratedChangedFiles = [
 ]
 // 2026-10-20 (test alignment): approved SW Story changes after the unused-demo removal that the lists above do not name.
 // Each comes from a user-requested commit merged into main as 553e4df. Regressions accept exactly these changes.
+// approvedMainCommit is the reviewed main merge the regressions treat as the accepted source state. overview.browser.mjs
+// (both modes) and storybook-unused-removal.browser.mjs keep their old baselines (50bf5bd, c8e5fbe) for the Story
+// inventory and declarations, and accept only the changes named in this file. For the source paths they guard (overview:
+// packages/sw/src; unused-removal: also the SW ai/package files, the other packages, Overview, Dropdown CSF, assets and
+// .storybook) they require no difference from this commit (integratedChangedFiles excepted) and report the diff from the
+// old baseline as sinceBaseline only.
+// Update it only after a merge into main whose Story and product source changes were all approved, in the same change
+// that records that merge's approved Story additions, removals, moves and tag changes in the lists of this file.
+// Never move it to make a failing check pass, and never to a commit that carries unreviewed Story or source changes.
+// A new main HEAD alone is no reason to move it: no script or workflow updates it automatically; it changes only in a
+// reviewed test-only commit (docs/sw/sw-test-regression-baseline-2026-10-20.md §9).
 export const approvedMainCommit = '553e4df4a865aaf6514b1c2b86cb2e3e9a658e5f'
 // 170a5c2: the SW/Header sidebar page of the home menu (the moved verification Stories are movedHomeMenuIds).
 export const homeMenuSidebarIds = ['sw-header--home-menu']