App Server host and connection lifecycle

ServiceHost owns one DeepCodeApplication; RpcPeer owns one client's protocol state and delivery. Desktop's stdio relay, TUI, headless execution and the browser authenticate with the local service.

Desktop native relay / TUI / CLI / Web
  authenticated HTTP and WebSocket
    ServiceHost                     application and shared watchers
      RpcPeer A                     one client's protocol and subscriptions
      RpcPeer B                     independent connection and bounded delivery

Ownership

• ServiceHost.start() installs one terminal, Skill, Plugin, MCP, and settings notification subscription set. Opening another peer does not add watchers.
• ServiceHost.connect(send) starts a peer over complete encoded RPC frames. Transport adapters own authentication, framing, and bounded/cancellable I/O. The host does not authenticate a caller simply because it can call connect.
• RpcPeer.receive(frame) serializes that peer's requests and output. Request IDs and initialization belong to the peer, not to the application.
• EOF, peer shutdown, or a write error releases that peer's subscriptions. It does not close the application, cancel Turns, or end terminal sessions.
• ServiceHost.close() releases all peers and shared subscriptions, then closes the application. Application cleanup failures are surfaced and may be retried. Partial startup failure also releases the resources already registered.

Notification delivery

Shared callbacks enqueue notifications into each initialized peer's bounded queue. They never write directly to a client's transport. A slow writer can delay its own RPC output, but cannot block the host from notifying another client. A write failure closes only the affected peer.

Durable events continue through the existing per-peer EventBroker subscription. Message limits and replay-page fitting are preserved. Queue overflow emits the existing server.warning shape with a NOTIFICATION_QUEUE_OVERFLOW code and a dropped count. Durable history is recoverable through event/replay; transient state notifications require a fresh read. Terminal output has bounded byte replay with truncation and exit metadata; input is not automatically replayed.

The peer's send callback must terminate or raise when its transport disconnects. The host does not close arbitrary caller-owned file descriptors or interrupt a blocked readline. Each transport must unblock its own reader/writer during shutdown. The stdio relay owns and closes its local connection.

Verification

tests/app_server/test_host.py checks that an admitted task completes with no clients, a new client can read and replay the result, another client survives EOF/shutdown/write failure, shared watchers survive disconnect, and a slow client does not block other clients. It also checks partial startup cleanup, retryable application cleanup and stdio relay EOF behavior.

Existing App Server protocol, framing, execution, workflow, replay, and cross-process application tests remain the compatibility baseline.