## Proposal Use assistant-ui standalone Elements for conversation controls, installed the same way as #306 (shadcn CLI into the generated directory, thin Chopin adapters, no `@assistant-ui/react` runtime): - [Message queue](https://www.assistant-ui.com/elements/message-queue) for the `chat:queue` waiting list, with unqueue as its cancel action. - [Stopped run](https://www.assistant-ui.com/elements/stopped-run) for `chat:abort` and `chat:resume`: the partial answer stays and Continue is one tap. - [Error state](https://www.assistant-ui.com/elements/error-state) for failed turns and system error entries, with retry where Chopin supports it.

## Acceptance criteria - [ ] The wire protocol is unchanged and the existing queue/abort/resume semantics hold, including persistence before publication. - [ ] Accessible names are kept, and reduced motion is respected. - [ ] `bun test`, `bun run types` and `bun run ci` pass. Playwright covers queue, stop/resume and error states.

## Related - #306: assistant-ui Elements adoption. This is a later layer of that stack.

Assistant-workflow: inline Assistant-duration: unmeasured Assistant-verification: code inspection passed: mapped existing Chopin features to the assistant-ui Elements catalog (standalone elements-* registry items, no @assistant-ui/react runtime)