## Why
MCP connection reconciliation can otherwise reuse a client after its service or
underlying transport has stopped.
## What changed
- Add `RmcpClient::is_closed` to report closed client, service, and transport
states.
- Exclude closed clients when selecting a reusable MCP connection so
reconciliation starts a replacement.
## Testing
- Add a reconciliation test that disconnects an in-process MCP transport and
verifies that its connection is replaced.
GitOrigin-RevId: 366a85c9959dbe1763923d7e33a4ecf52d9c3c6a