Connect ACP agents to OpenPencil MCP tools

Pass openpencil-mcp as a stdio MCP server to the ACP session so
agents get all design tools (create shapes, render JSX, export
images, etc.) instead of just plain conversation.

- Add makeFigma option to createServer for external FigmaAPI injection
- Skip file lifecycle tools (open/save/new) when using external FigmaAPI
- Pass MCP server config in ACP newSession mcpServers
- Add bun to Tauri shell scope for MCP server subprocess

desktop/capabilities/default.json

@@ -24,7 +24,8 @@
       "allow": [
         { "name": "claude-code-acp", "cmd": "claude-code-acp", "args": true },
         { "name": "codex-acp", "cmd": "codex-acp", "args": true },
-        { "name": "gemini", "cmd": "gemini", "args": true }
+        { "name": "gemini", "cmd": "gemini", "args": true },
+        { "name": "bun", "cmd": "bun", "args": true }
       ]
     },
     "shell:allow-stdin-write",

packages/mcp/src/server.ts

@@ -22,6 +22,7 @@ type McpResult = { content: McpContent[]; isError?: boolean }
 export interface CreateServerOptions {
   enableEval?: boolean
   fileRoot?: string | null
+  makeFigma?: () => FigmaAPI
 }
 
 function ok(data: unknown): McpResult {
@@ -61,10 +62,13 @@ export function createServer(version: string, options: CreateServerOptions = {})
     ? null
     : resolve(options.fileRoot)
 
+  const externalMakeFigma = options.makeFigma ?? null
+
   let graph: SceneGraph | null = null
   let currentPageId: string | null = null
 
   function makeFigma(): FigmaAPI {
+    if (externalMakeFigma) return externalMakeFigma()
     if (!graph) throw new Error('No document loaded. Use open_file or new_document first.')
     const g = graph
     const api = new FigmaAPI(g)
@@ -112,6 +116,8 @@ export function createServer(version: string, options: CreateServerOptions = {})
   }
 
   const register = server.registerTool.bind(server) as (...args: unknown[]) => void
+
+  if (!externalMakeFigma) {
   register(
     'open_file',
     {
@@ -170,6 +176,7 @@ export function createServer(version: string, options: CreateServerOptions = {})
       }
     }
   )
+  } // end if (!externalMakeFigma)
 
   register(
     'export_image_file',

src/ai/acp-transport.ts

@@ -27,10 +27,14 @@ export class ACPChatTransport implements ChatTransport<UIMessage> {
   private session: ACPSession | null = null
   private agentDef: ACPAgentDef
   private cwd: string
+  private mcpCommand?: string
+  private mcpArgs: string[]
 
-  constructor(options: { agentDef: ACPAgentDef; cwd?: string }) {
+  constructor(options: { agentDef: ACPAgentDef; cwd?: string; mcpCommand?: string; mcpArgs?: string[] }) {
     this.agentDef = options.agentDef
     this.cwd = options.cwd ?? '.'
+    this.mcpCommand = options.mcpCommand
+    this.mcpArgs = options.mcpArgs ?? []
   }
 
   async sendMessages({
@@ -199,9 +203,13 @@ export class ACPChatTransport implements ChatTransport<UIMessage> {
       clientCapabilities: {}
     })
 
+    const mcpServers = this.mcpCommand
+      ? [{ name: 'open-pencil', command: this.mcpCommand, args: this.mcpArgs, env: [] }]
+      : []
+
     const sessionResult = await connection.newSession({
       cwd: this.cwd,
-      mcpServers: []
+      mcpServers
     })
 
     const session: ACPSession = {

src/composables/use-chat.ts

@@ -209,8 +209,20 @@ async function createACPTransport() {
   if (!agentDef) throw new Error(`Unknown ACP agent: ${agentId}`)
 
   const { ACPChatTransport } = await import('@/ai/acp-transport')
+  const { homeDir } = await import('@tauri-apps/api/path')
   await acpTransportInstance?.destroy()
-  const transport = new ACPChatTransport({ agentDef })
+
+  const mcpCommand = import.meta.env.DEV ? 'bun' : 'npx'
+  const mcpArgs = import.meta.env.DEV
+    ? [import.meta.env.VITE_PROJECT_ROOT + '/packages/mcp/src/index.ts']
+    : ['-y', '@open-pencil/mcp']
+
+  const transport = new ACPChatTransport({
+    agentDef,
+    cwd: await homeDir(),
+    mcpCommand,
+    mcpArgs
+  })
   acpTransportInstance = transport
   return transport
 }

vite.config.ts

@@ -15,6 +15,9 @@ import { automationPlugin } from './src/automation/vite-plugin'
 const host = process.env.TAURI_DEV_HOST
 
 export default defineConfig(async () => ({
+  define: {
+    'import.meta.env.VITE_PROJECT_ROOT': JSON.stringify(__dirname)
+  },
   resolve: {
     alias: {
       '@': resolve(__dirname, 'src'),