feat(sim): F4.2 the sim protocol, the simulation room and LocalSimHost; M9 measured

packages/protocol holds the one list of /sim messages and checks every
field, naming what is wrong. packages/sim has the simulation room for F and
the web worker: the document's snapshot at start, the engine's clock on the
wall clock with Java's speed as cable delay, subscriptions to cable
activity, a card's new frames and a program's new window lines, capture and
clock kept over a stop, the command line as first action, a core failure
told to every client. LocalSimHost mirrors the document into the worker and
back without echo. M9 in Chromium: 17 examples give the same capture as in
Node, character for character; the room runs in a real worker.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/sim/src/serveRoom.ts

@@ -0,0 +1,28 @@
+// The worker's side: a replica of the editor's document and the room that
+// reads it, ticking every TICK_MILLISECONDS.
+
+import * as Y from 'yjs';
+import { CHANNEL_ORIGIN, type ChannelMessage, type Port } from './channel.js';
+import { SimulationRoom, TICK_MILLISECONDS, type RoomOptions } from './room.js';
+
+export interface ServeOptions extends RoomOptions {
+  /** Calls `tick` every so many milliseconds. */
+  readonly every: (milliseconds: number, tick: () => void) => void;
+}
+
+export function serveRoom(port: Port, options: ServeOptions): SimulationRoom {
+  const doc = new Y.Doc();
+  doc.on('update', (update: Uint8Array, origin: unknown) => {
+    if (origin !== CHANNEL_ORIGIN) port.postMessage({ type: 'doc', update });
+  });
+  const room = new SimulationRoom(doc, options);
+  const client = room.connect((message) => port.postMessage({ type: 'host', message }));
+  port.addEventListener('message', (event) => {
+    const data = event.data as ChannelMessage;
+    if (data?.type === 'doc') Y.applyUpdate(doc, data.update, CHANNEL_ORIGIN);
+    else if (data?.type === 'client') room.receive(client, data.message);
+  });
+  port.start?.();
+  options.every(TICK_MILLISECONDS, () => room.tick());
+  return room;
+}