The current slice supports server- and Session-scoped facet-service routing and multi-presentation attachment. RoutedServerServiceHost.attachClient() creates one connection-scoped server service endpoint with narrow attachment-management capabilities. RoutedSessionHandle.attachClient() returns a presentation-scoped Session capability. Its invokeService() forwards an opaque service/member envelope to the selected Session endpoint; the server validates the attachment route but does not load the facet contract.

server service calls and subscriptions route opaquely through the connection's RoutedServerServiceAttachment;
the application-owned SessionDirectory projects the private catalog into replicated presentation-safe state;
the application-owned SessionManagement creates, removes, attaches, and detaches Sessions without exposing route IDs in business results;
attachment changes are published out of band after the router installs or clears the live route;
Session service calls route through invokeService without server-side business-payload decoding;
service subscription updates remain scoped to the requesting attachment;
application observations such as transcripts route as ordinary service state without server-owned business schemas.

A Session may have multiple presentation attachments. Repeating attach from one connection is idempotent; every successful attachment has a server-generated attachmentId delivered only as routing control data. Session requests carry { serverId, sessionId, attachmentId }, and the server rejects stale or mismatched routes. Losing a connection rejects its local responses but releases its attachment only after admitted service calls settle. The host decides when zero presentation demand and worker-local Harness activity permit worker retirement. Server shutdown closes every routed Session handle, releasing its worker and Session writer ownership.

import { randomUUID } from "node:crypto";
import {
  type RoutedServerServiceHost,
  type RoutedSessionHandle,
  type ServerHost,
  type SessionMetadata,
  SessionNotFoundError,
} from "@earendil-works/pi-server";
import { createUnixServer, getUnixSocketPath } from "@earendil-works/pi-server/unix";

interface StoredSession extends SessionMetadata {
  path: string;
}

async function startServer(
  serverServices: RoutedServerServiceHost,
  sessions: Map<string, StoredSession>,
  openRoutedSession: (session: StoredSession) => Promise<RoutedSessionHandle>,
) {
  const host: ServerHost<StoredSession> = {
    serverServices,
    async resolveSession(sessionId) {
      const metadata = sessions.get(sessionId);
      if (!metadata) throw new SessionNotFoundError(`Unknown session: ${sessionId}`);
      return metadata;
    },
    openSession: (metadata) => openRoutedSession(metadata),
  };

  const serverId = randomUUID();
  const server = createUnixServer(host, {
    serverId,
    path: getUnixSocketPath(serverId, "/run/user/1000/pi"),
  });
  await server.start();
  return server;
}

Applications supply a required server service host, a bounded Session resolver, and a routed Session factory. SessionMetadata only requires an id; applications may extend it with their own storage fields. Session discovery and management are application-owned services; the protocol server only asks the resolver for metadata when routing an attachment. The host owns acquiring the worker-local Session and Harness. Failures are cleaned up in that worker. Neither an open JavaScript Session nor a Harness crosses the process boundary.

serverId is a logical identity supplied by the launcher, not a socket address. The Unix preset requires an explicit physical path; getUnixSocketPath() derives one from a caller-selected directory. Choose a short, private runtime directory rather than deriving the route from an unbounded home-directory path. A long-lived launcher can reuse the same ID and path when replacing a server process.

Server composes transports through ServerListener; peer authentication remains application policy and is not implemented by the experimental Unix transport. The Unix submodule provides createUnixListener() and createUnixServer(). Low-level routed-envelope validation, CBOR, and framing come from @earendil-works/pi-protocol; Chord owns service-control parsing, error codes, snapshots and updates, and each subscription's replicated-state encoder.

Server and worker lifecycle is managed outside the public Pi protocol. The replaceable application server converts connection attachments into private demand updates; the worker combines generation-tagged demand with authoritative Harness activity. The experimental coordinator only supplies stable routing and reports generic server-generation connection changes.