feat(mcp): add stdio + streamable HTTP transports, CLI, and smoke test

- connectStdio(server): wires the MCP server to StdioServerTransport.
- connectHttp(server, port): wires the MCP server to
  StreamableHTTPServerTransport over node:http. Returns a handle with
  port and close().
- bin/pascal-mcp.ts: CLI entrypoint with --stdio (default), --http,
  --port, --scene, --help, --version. Loads node-shims before any
  core import. Logs to stderr (stdio transport uses stdout for
  JSON-RPC).
- scripts/smoke.ts: end-to-end smoke — spawns the stdio bin, connects
  as an MCP Client, exercises get_scene, create_level, validate_scene,
  undo.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/mcp/src/bin/pascal-mcp.ts

@@ -0,0 +1,85 @@
+#!/usr/bin/env node
+// Load shims FIRST so any subsequent core import sees the RAF polyfill.
+import '../bridge/node-shims'
+
+import { readFileSync } from 'node:fs'
+import { parseArgs } from 'node:util'
+import { SceneBridge } from '../bridge/scene-bridge'
+import { version } from '../index'
+import { createPascalMcpServer } from '../server'
+import { connectHttp } from '../transports/http'
+import { connectStdio } from '../transports/stdio'
+
+const HELP = `pascal-mcp — MCP server for the Pascal editor
+
+USAGE:
+  pascal-mcp [--stdio | --http --port <n>] [--scene <path>]
+
+OPTIONS:
+  --stdio          Use stdio transport (default)
+  --http           Use Streamable HTTP transport
+  --port <n>       HTTP port (default 3917)
+  --scene <path>   Initial scene JSON to load
+  --version        Print version
+  --help           Print this help
+`
+
+async function main(): Promise<void> {
+  const { values } = parseArgs({
+    options: {
+      stdio: { type: 'boolean', default: false },
+      http: { type: 'boolean', default: false },
+      port: { type: 'string', default: '3917' },
+      scene: { type: 'string' },
+      help: { type: 'boolean', default: false },
+      version: { type: 'boolean', default: false },
+    },
+  })
+
+  if (values.help) {
+    console.log(HELP)
+    process.exit(0)
+  }
+
+  if (values.version) {
+    console.log(version)
+    process.exit(0)
+  }
+
+  const bridge = new SceneBridge()
+  if (values.scene) {
+    const raw = readFileSync(values.scene, 'utf8')
+    bridge.loadJSON(raw)
+  } else {
+    bridge.loadDefault()
+  }
+
+  const server = createPascalMcpServer({ bridge })
+
+  if (values.http) {
+    const portNum = Number.parseInt(values.port ?? '3917', 10)
+    if (!Number.isFinite(portNum) || portNum < 0 || portNum > 65535) {
+      throw new Error(`invalid --port value: ${values.port}`)
+    }
+    const handle = await connectHttp(server, portNum)
+    console.error(`[pascal-mcp] HTTP server listening on :${handle.port}`)
+    const shutdown = async () => {
+      try {
+        await handle.close()
+      } finally {
+        process.exit(0)
+      }
+    }
+    process.on('SIGINT', shutdown)
+    process.on('SIGTERM', shutdown)
+  } else {
+    // --stdio is the default when no transport flag is passed.
+    await connectStdio(server)
+    console.error('[pascal-mcp] stdio server running')
+  }
+}
+
+main().catch((err) => {
+  console.error('[pascal-mcp] fatal:', err instanceof Error ? (err.stack ?? err.message) : err)
+  process.exit(1)
+})