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/protocol/src/sim.ts

@@ -0,0 +1,123 @@
+// The messages between the editor and a simulation room (plan §6.4) — the
+// one list both sides import, so that a kind one side sends and the other
+// does not know is a reported error, never silently dropped (Scratch's trap
+// 6.1). The room runs on F (RemoteSimHost, F5) or in a web worker
+// (LocalSimHost); the messages are the same.
+
+import type { CaptureRow } from '@mdg-filius/core';
+
+export const SIM_PROTOCOL_VERSION = 1;
+
+/** The programs whose windows a client can watch and act in. */
+export const APP_KINDS = ['terminal', 'webBrowser', 'webServer', 'emailClient', 'emailServer', 'echoServer', 'simpleClient', 'gnutella'] as const;
+export type AppKind = (typeof APP_KINDS)[number];
+
+/**
+ * What a client subscribes to: which cables carry frames (`activity`), a
+ * card's capture (`trace:<portId>`), a program's window
+ * (`app:<nodeId>/<app>`).
+ */
+export type Topic = 'activity' | `trace:${string}` | `app:${string}/${AppKind}`;
+
+export const CLIENT_MESSAGE_KINDS = ['sub', 'unsub', 'start', 'stop', 'speed', 'input'] as const;
+export type ClientMessageKind = (typeof CLIENT_MESSAGE_KINDS)[number];
+
+export type ClientMessage =
+  | { readonly v: 1; readonly kind: 'sub'; readonly topics: readonly Topic[] }
+  | { readonly v: 1; readonly kind: 'unsub'; readonly topics: readonly Topic[] }
+  /** Starts the simulation with the document as it is now. */
+  | { readonly v: 1; readonly kind: 'start' }
+  | { readonly v: 1; readonly kind: 'stop' }
+  /** Java's speed slider, 1 to 100 per cent: how long a frame takes over a cable. */
+  | { readonly v: 1; readonly kind: 'speed'; readonly value: number }
+  /** An action in a program's window, answered by `ack` or `error` with the same reqId. */
+  | {
+      readonly v: 1;
+      readonly kind: 'input';
+      readonly node: string;
+      readonly app: AppKind;
+      readonly action: string;
+      readonly args: Readonly<Record<string, unknown>>;
+      readonly reqId: string;
+    };
+
+export const HOST_MESSAGE_KINDS = ['state', 'activity', 'trace', 'app', 'ack', 'error'] as const;
+export type HostMessageKind = (typeof HOST_MESSAGE_KINDS)[number];
+
+export type SimMode = 'design' | 'simulation';
+
+/** A frame's rows as the capture window shows them: with addresses (data exchange) and layered. */
+export interface TraceFrame {
+  readonly number: number;
+  readonly rows: readonly CaptureRow[];
+  readonly layeredRows: readonly CaptureRow[];
+}
+
+/** engineFailed: the core threw (a part it has not got yet, such as remote links); the room is back in design mode. */
+export const ERROR_CODES = ['badMessage', 'badVersion', 'unknownKind', 'badTopic', 'notRunning', 'unknownNode', 'unknownApp', 'unknownAction', 'badArgs', 'engineFailed'] as const;
+export type ErrorCode = (typeof ERROR_CODES)[number];
+
+export type HostMessage =
+  /** The room's mode, speed and time; sent to every client on a change and when it connects. */
+  | { readonly v: 1; readonly kind: 'state'; readonly mode: SimMode; readonly speed: number; readonly t: number }
+  /** The cables that carried a frame since the last tick. */
+  | { readonly v: 1; readonly kind: 'activity'; readonly links: readonly string[] }
+  /** A card's new frames; on subscribing, all it holds (`reset`). */
+  | { readonly v: 1; readonly kind: 'trace'; readonly portId: string; readonly frames: readonly TraceFrame[]; readonly reset: boolean }
+  /** A program's new window lines from line `from` on; on subscribing, all (from 0). */
+  | { readonly v: 1; readonly kind: 'app'; readonly node: string; readonly app: AppKind; readonly from: number; readonly lines: readonly unknown[] }
+  | { readonly v: 1; readonly kind: 'ack'; readonly reqId: string }
+  | { readonly v: 1; readonly kind: 'error'; readonly code: ErrorCode; readonly reqId?: string; readonly detail?: string };
+
+export type Parsed<T> = { readonly message: T } | { readonly error: { readonly code: ErrorCode; readonly detail: string } };
+
+const isRecord = (value: unknown): value is Record<string, unknown> => typeof value === 'object' && value !== null && !Array.isArray(value);
+const bad = (code: ErrorCode, detail: string) => ({ error: { code, detail } });
+
+/** Whether a topic is one the room knows. */
+export function isTopic(value: unknown): value is Topic {
+  if (value === 'activity') return true;
+  if (typeof value !== 'string') return false;
+  if (value.startsWith('trace:')) return value.length > 'trace:'.length;
+  const app = /^app:([^/]+)\/(.+)$/.exec(value);
+  return app !== null && (APP_KINDS as readonly string[]).includes(app[2]!);
+}
+
+/** A client's message as the room reads it: every field checked, an unknown kind named. */
+export function parseClientMessage(value: unknown): Parsed<ClientMessage> {
+  if (!isRecord(value)) return bad('badMessage', 'not an object');
+  if (value.v !== SIM_PROTOCOL_VERSION) return bad('badVersion', `version ${String(value.v)}`);
+  const kind = value.kind;
+  if (!(CLIENT_MESSAGE_KINDS as readonly unknown[]).includes(kind)) return bad('unknownKind', `kind ${String(kind)}`);
+  switch (kind as ClientMessageKind) {
+    case 'sub':
+    case 'unsub': {
+      const topics = value.topics;
+      if (!Array.isArray(topics)) return bad('badMessage', 'topics is no list');
+      const unknown = topics.find((topic) => !isTopic(topic));
+      if (unknown !== undefined) return bad('badTopic', `topic ${String(unknown)}`);
+      return { message: { v: 1, kind: kind as 'sub' | 'unsub', topics: topics as Topic[] } };
+    }
+    case 'start':
+    case 'stop':
+      return { message: { v: 1, kind: kind as 'start' | 'stop' } };
+    case 'speed':
+      if (typeof value.value !== 'number' || !Number.isFinite(value.value)) return bad('badMessage', 'speed is no number');
+      return { message: { v: 1, kind: 'speed', value: value.value } };
+    case 'input': {
+      const { node, app, action, args, reqId } = value;
+      if (typeof reqId !== 'string') return bad('badMessage', 'reqId is no string');
+      if (typeof node !== 'string' || typeof action !== 'string' || !isRecord(args)) return bad('badMessage', 'input needs node, action and args');
+      if (!(APP_KINDS as readonly unknown[]).includes(app)) return bad('unknownApp', `app ${String(app)}`);
+      return { message: { v: 1, kind: 'input', node, app: app as AppKind, action, args, reqId } };
+    }
+  }
+}
+
+/** A host's message as the editor reads it: the kind known, else an error the editor shows. */
+export function parseHostMessage(value: unknown): Parsed<HostMessage> {
+  if (!isRecord(value)) return bad('badMessage', 'not an object');
+  if (value.v !== SIM_PROTOCOL_VERSION) return bad('badVersion', `version ${String(value.v)}`);
+  if (!(HOST_MESSAGE_KINDS as readonly unknown[]).includes(value.kind)) return bad('unknownKind', `kind ${String(value.kind)}`);
+  return { message: value as unknown as HostMessage };
+}