## What changed
- Add experimental `mcpServer/event/stream/start` and `mcpServer/event/stream/stop` requests for hosted apps, plus `mcpServer/event/stream/notification` forwarding.
- Scope subscriptions to the owning app-server connection and subscribed thread, enforce unique IDs and a per-connection limit, and clean them up when the thread is unsubscribed or the connection closes.
- Wait for the MCP active notification before completing startup, retry streams that close immediately, and terminate them when authentication or hosted runtime ownership changes.
## Testing
- Add an app-server integration test covering activation, event forwarding, duplicate subscription rejection, and explicit cancellation.
GitOrigin-RevId: 8a6fc1615adfc5af7e67def3b824fa5909ab3e7b
