Merge origin/master into worktree-websettings

ui-sidebar shell landed on master (#643: geometry-only shell, the
browsing region moved to the sidebar.workspaces slot); this branch's
sidebar.settings foot seat re-applies on top — the hardcoded foot row
becomes the seat, the seat rides the railIn crossfade, and the shell
spec's renderSlot stub key-splits region vs settings.

scripts/verify-package-readme-model-experience.ts

@@ -93,6 +93,7 @@ const SENTENCE_MODEL_EXPERIENCE: Readonly<Record<string, SentenceContract>> = {
   'packages/support/agent-loop-testkit': { kind: 'none', reason: 'The test helper mounts services but neither drives nor modifies model requests.' },
   'packages/support/invariants': { kind: 'none', reason: 'The observer validates requests but never rewrites their context.' },
   'packages/support/loader-smoke': { kind: 'none', reason: 'The test harness observes child-process streams without changing live requests.' },
+  'packages/support/llm-mock-server': { kind: 'none', reason: 'The test server substitutes provider wire behavior without invoking a real model.' },
   'packages/support/llm-replay': { kind: 'none', reason: 'The keyless adapter invokes no provider model.' },
   'packages/tasks/tasks': { kind: 'indirect', reason: 'Producer and control-surface plugins own all model rendering over the task registry.' },
   'packages/examples/acp-demo': { kind: 'indirect', reason: 'The app bundle delegates request composition to dsh-agent-spine-demo and dsh-acp.' },