fix: add compiled MCP server module for --mode mcp support

Create src/mcp-server.ts with dynamic imports to bypass TypeScript's
static module resolution for @modelcontextprotocol/sdk subpath exports
that use wildcard patterns (./*) without matching type declarations.

src/mcp-server.ts

@@ -0,0 +1,79 @@
+interface McpTool {
+  name: string
+  description: string
+  parameters: Record<string, unknown>
+  execute(
+    toolCallId: string,
+    params: Record<string, unknown>,
+    signal?: AbortSignal,
+    onUpdate?: unknown,
+  ): Promise<{
+    content: Array<{ type: string; text?: string; data?: string; mimeType?: string }>
+  }>
+}
+
+// MCP SDK subpath imports use wildcard exports (./*) that NodeNext resolves
+// at runtime but TypeScript cannot statically type-check. We construct the
+// specifiers dynamically so tsc treats them as `any`.
+const MCP_PKG = '@modelcontextprotocol/sdk'
+
+export async function startMcpServer(options: {
+  tools: McpTool[]
+  version?: string
+}): Promise<void> {
+  const { tools, version = '0.0.0' } = options
+
+  const serverMod = await import(`${MCP_PKG}/server`)
+  const stdioMod = await import(`${MCP_PKG}/server/stdio`)
+  const typesMod = await import(`${MCP_PKG}/types`)
+
+  const Server = serverMod.Server
+  const StdioServerTransport = stdioMod.StdioServerTransport
+  const { ListToolsRequestSchema, CallToolRequestSchema } = typesMod
+
+  const toolMap = new Map<string, McpTool>()
+  for (const tool of tools) {
+    toolMap.set(tool.name, tool)
+  }
+
+  const server = new Server(
+    { name: 'gsd', version },
+    { capabilities: { tools: {} } },
+  )
+
+  server.setRequestHandler(ListToolsRequestSchema, async () => ({
+    tools: tools.map((t: McpTool) => ({
+      name: t.name,
+      description: t.description,
+      inputSchema: t.parameters,
+    })),
+  }))
+
+  server.setRequestHandler(CallToolRequestSchema, async (request: any) => {
+    const { name, arguments: args } = request.params
+    const tool = toolMap.get(name)
+    if (!tool) {
+      return {
+        isError: true,
+        content: [{ type: 'text' as const, text: `Unknown tool: ${name}` }],
+      }
+    }
+
+    try {
+      const result = await tool.execute(`mcp-${Date.now()}`, args ?? {}, undefined, undefined)
+      const content = result.content.map((block: any) => {
+        if (block.type === 'text') return { type: 'text' as const, text: block.text ?? '' }
+        if (block.type === 'image') return { type: 'image' as const, data: block.data ?? '', mimeType: block.mimeType ?? 'image/png' }
+        return { type: 'text' as const, text: JSON.stringify(block) }
+      })
+      return { content }
+    } catch (err: unknown) {
+      const message = err instanceof Error ? err.message : String(err)
+      return { isError: true, content: [{ type: 'text' as const, text: message }] }
+    }
+  })
+
+  const transport = new StdioServerTransport()
+  await server.connect(transport)
+  process.stderr.write(`[gsd] MCP server started (v${version})\n`)
+}