## Why
Event subscriptions may need to outlive the MCP runtime associated with a task.
## What changed
- Add `McpEventStreamOpener`, which retains the hosted Apps MCP connection settings and opens each event stream with an independent client.
- Keep subscription cancellation tied to account changes and removal of the task's event server, including when cancellation ownership is forwarded across runtime replacement.
- Expose the opener and cancellation forwarding through `McpResourceClient`.
## Testing
Add an HTTP transport test that shuts down the runtime, refreshes credentials for the same account, and verifies that a new event stream connects with the current authorization and receives notifications.
GitOrigin-RevId: e102aa382e63121661ff0567f7523515e459922d
53691bad98