## Why
Cloud conversations previously used the model returned on activation without exposing model discovery or supporting model changes from the TUI.
## What changed
- Fetch the account-scoped Cloud catalog on demand through `/v2/models`, independently of the submission and attachment queue.
- Let users stage a supported model and reasoning effort for the next new turn in the current conversation. Send these settings with the user message and show acceptance after successful admission.
- Show a loading picker when the catalog is empty, preserve compatibility with Cloud servers that lack discovery, and discard stale catalog results and selections when the account changes.
## Testing
Add coverage for catalog request parameters and queue bypass, deferred discovery and compatibility, model and effort serialization, admission outcomes, account invalidation, and opening the picker after discovery.
GitOrigin-RevId: 2cd0e7fe5f760d4da9258eefe9f0dcbcd23f9b07
## What changed
- Add `CloudClient` and integrate it with `AppServerClient` and `AppServerRequestHandle` for requests, notifications, server-request replies, events, and shutdown.
- Keep retained request and reply handles bound to their cloud backend, with event delivery independent of request completion and a timeout for shutdown.
- Return no platform or Codex home metadata for cloud clients, and reject TUI filesystem operations for this backend.
## Testing
Add tests for backend ownership of retained handles, independent event delivery, errors after the command receiver closes, and shutdown timeouts when the worker does not respond.
GitOrigin-RevId: 4cf308dc0ea6fa6e7b14dd4542d93e8030b0162d
Benjamin Carlsson