chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/server/src/connection.ts

@@ -0,0 +1,37 @@
+import type { ServiceStateEncoder } from "@earendil-works/chord";
+import type { ClientMessageDecoder, RpcTarget } from "@earendil-works/pi-protocol";
+
+import type { MaybePromise, RoutedServerServiceAttachment } from "./types.ts";
+
+/** An established, authorized ordered byte connection. */
+export interface ByteConnection {
+	readonly closed: boolean;
+	send(chunk: Uint8Array): Promise<void>;
+	close(finalChunk?: Uint8Array): MaybePromise<void>;
+}
+
+export interface ByteConnectionHandler {
+	onData(chunk: Uint8Array): void;
+	onClose(): void;
+	onError(error: Error): void;
+}
+
+export type ByteConnectionAcceptor = (connection: ByteConnection) => ByteConnectionHandler;
+
+export type ConnectionStage = "awaitingHello" | "handshaking" | "ready" | "closing" | "closed";
+
+export interface ConnectionState {
+	connection: ByteConnection;
+	decoder: ClientMessageDecoder;
+	serviceStateEncoders: Map<string, ServiceStateEncoder>;
+	stage: ConnectionStage;
+	disconnected: boolean;
+	handshake?: Promise<void>;
+	handshakeTimeout: NodeJS.Timeout;
+	serverServices?: RoutedServerServiceAttachment;
+	activeRequests: Map<string, { controller: AbortController; target: RpcTarget }>;
+}
+
+export function isTerminalConnection(state: ConnectionState): boolean {
+	return state.disconnected || state.stage === "closing" || state.stage === "closed";
+}