A follow-up sweep against #6381 found the branch still carrying the
pre-simplification forms it replaced, which my earlier fix had papered
over with a compat utility instead of finishing the migration:

- ChatView now uses main's inlined titlebar sizing and the
  data-workspace-titlebar-controls hook on both control clusters. The
  class-based markup was silently missing the themed-toggle bridge
  (html[data-theme-id] [data-workspace-titlebar-controls] …), so custom
  themes lost their titlebar accent in the thread view.
- The scroll-to-end pill becomes main's Button size="xs" variant="glass"
  instead of a hand-rolled button recreating it.
- MessagesTimeline uses main's consolidated topbar-scroll-fade utility;
  the byte-identical chat-timeline-scroll-fade copy and the
  workspace-topbar compat utility are gone.
- The composer-glass dark rules move into nested @variant dark like
  main's (the raw .dark duplicates could drift from the nested copies
  they shadowed), including the branch-only queue strip.
- The pre-#6381 dialog-glass/dialog-backdrop/dropdown-glass class rules
  and their .dark variants are deleted: the #6381 utilities plus
  call-site shadow utilities own every declaration, and the stale
  dropdown rule still had the saturate-less backdrop-filter. The dead
  model-picker-surface dark rule goes with them.

index.css now has zero raw .dark selectors outside the variant
definitions, matching the doctrine in
.macroscope/check-run-agents/ui-consistency.md. Verified against the
emitted production CSS: dark variants compile to :is(.dark,.dark *) with
their @supports color-mix fallbacks intact.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>