48px sticky top strip per docs/specs/2026-04-11-nexus-layout-overhaul.md
§4.2. Composes ModeBreadcrumb (left) + CmdKButton and GlobalMicButton
(right) inside a <header aria-label="Top bar"> landmark.
Completes the frame component set for Phase 8. The next task (task 6)
rewrites Layout.tsx to mount IconRail + TopStrip as the new global
chrome and delete the old sidebar/ChatPanel/PropertiesPanel/
BreadcrumbBar combination.
Part of Phase 8 of the Nexus layout overhaul (task 5 of 7).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
