## Why
Server request IDs can be reused across connections. Retained replies need to target the connection that emitted the request, even if the UI selection later changes.
## What changed
- Expose `AppServerReplyHandle` through `AppServerRequestHandle::server_request_reply_handle`, capturing the originating client and request ID for explicit `resolve` or `reject` calls.
- Share single-use completion state across clones so only the first reply is submitted. Dropping a handle sends nothing; stale connections return I/O errors without retrying or switching connections.
- Route existing client reply methods through request handles and use the new API in the managed worktree model test.
## Testing
Add in-process and WebSocket tests for replies on separate connections with identical request IDs, rejection routing, duplicate completion, and stale handles after worker shutdown. Also check that debug output redacts handle details.
GitOrigin-RevId: 940d0951ab67529b05919ca8ec7adb5813834b8c
Benjamin Carlsson
8c0f701167