Simplification per spec: the menu tracks state through the URL alone.
Land on /docs: fully closed, headers only (an explicit home rule now
overrides the contains-URL rule, since the root overview doc lives in
Getting Started and would otherwise auto-open it). Land on any doc page:
its containing section + group render open at first paint, current link
bold — no JS, no jump, arrows consistent. Navigate elsewhere: old
closes, new opens.
Deleted: docs_nav cookie const/parse, ApplyNavOverrides, cookie write +
collect/persist helpers in web/src/docs.ts, data-key attributes in the
sidebar templ, and the first-section-open fallback (docs home used to
force-open the first section — spec'd as closed).
toggleCollapsible remains for in-page peeking; purely ephemeral.
The [data-collapsed=true] CSS from the previous round stays — it is what
makes the server-rendered state actually hide sections at paint (the
original bug was that this CSS never existed).
Tests: TestBuildNavigationNothingCurrent now asserts zero sections open
on unmatched paths; TestBuildNavigation asserts Getting Started closed
on a device page (no site-wide pin). make test green; 146 vitests; live
verified: home 0 expanded, doc pages exactly 2 (section+group).
John O'Keefe
73e8cdef4b