## Why
Cancelling an in-flight MCP elicitation could leave its response handler registered in the shared router.
## What changed
- Remove an elicitation from the router when its pending request future is dropped.
- Keep cleanup scoped to the cancelled request so other pending elicitations remain routable.
## Testing
Added a test that cancels one of two pending elicitations, verifies the cancelled request can no longer be resolved, and confirms the other request still completes.
GitOrigin-RevId: 9a10360459f0b39552d9d29a6e1b867c1f09e97d