Swaps the rendering layer only. Chat store logic, keyboard handling, and the /chat-run Socket.IO contract are untouched, so a mixed UI cannot hide a chat regression behind a library swap. Arco's dropdowns take their items from a #content slot of a-doption children rather than a droplist prop, and Arco Triggers cannot be nested, so the two toolbar menus lost their a-tooltip in favour of a native title. Both rules are recorded in docs/arco-mapping.md, and tests/e2e/chat-input-dropdown.spec.ts plus tests/e2e/chat-rendering-smoke.spec.ts keep the menus, the streaming markdown rendering, and the no-Arco-inside-the-bubble red line from regressing silently.
Chat Chain Change Fragments
Add one Markdown fragment per PR when a change touches the Chat session chain,
Agent Bridge, compression, or Group Chat runtime paths documented in
docs/cli-chat-sessions.md.
Do not append new rows to docs/cli-chat-sessions.md. Keeping one fragment per
PR avoids merge conflicts when multiple branches change the chat chain at the
same time.
Use this shape:
---
date: YYYY-MM-DD
pr: 1234
feature: Short feature name
impact: One-sentence behavior impact
---
Optional extra notes.
If the PR number is not known yet, use pr: pending while the branch is local,
then update that same fragment after the PR is opened.