diff --git a/scripts/runtime-postbuild.mjs b/scripts/runtime-postbuild.mjs
index ef78dd0d030..454878cad5e 100644
--- a/scripts/runtime-postbuild.mjs
+++ b/scripts/runtime-postbuild.mjs
@@ -1,16 +1,48 @@
-import { pathToFileURL } from "node:url";
+import fs from "node:fs";
+import path from "node:path";
+import { fileURLToPath, pathToFileURL } from "node:url";
 import { copyBundledPluginMetadata } from "./copy-bundled-plugin-metadata.mjs";
 import { copyPluginSdkRootAlias } from "./copy-plugin-sdk-root-alias.mjs";
 import { stageBundledPluginRuntimeDeps } from "./stage-bundled-plugin-runtime-deps.mjs";
 import { stageBundledPluginRuntime } from "./stage-bundled-plugin-runtime.mjs";
 import { writeOfficialChannelCatalog } from "./write-official-channel-catalog.mjs";
 
+const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+
+/**
+ * Copy static (non-transpiled) runtime assets that are referenced by their
+ * source-relative path inside bundled extension code.
+ *
+ * Each entry: { src: repo-root-relative source, dest: dist-relative dest }
+ */
+const STATIC_EXTENSION_ASSETS = [
+  // acpx MCP proxy — co-deployed alongside the acpx index bundle so that
+  // `path.resolve(dirname(import.meta.url), "mcp-proxy.mjs")` resolves correctly
+  // at runtime (see extensions/acpx/src/runtime-internals/mcp-agent-command.ts).
+  {
+    src: "extensions/acpx/src/runtime-internals/mcp-proxy.mjs",
+    dest: "dist/extensions/acpx/mcp-proxy.mjs",
+  },
+];
+
+function copyStaticExtensionAssets() {
+  for (const { src, dest } of STATIC_EXTENSION_ASSETS) {
+    const srcPath = path.join(ROOT, src);
+    const destPath = path.join(ROOT, dest);
+    if (fs.existsSync(srcPath)) {
+      fs.mkdirSync(path.dirname(destPath), { recursive: true });
+      fs.copyFileSync(srcPath, destPath);
+    }
+  }
+}
+
 export function runRuntimePostBuild(params = {}) {
   copyPluginSdkRootAlias(params);
   copyBundledPluginMetadata(params);
   writeOfficialChannelCatalog(params);
   stageBundledPluginRuntimeDeps(params);
   stageBundledPluginRuntime(params);
+  copyStaticExtensionAssets();
 }
 
 if (import.meta.url === pathToFileURL(process.argv[1] ?? "").href) {
diff --git a/tsdown.config.ts b/tsdown.config.ts
index c20b1cf7701..acbaabe3734 100644
--- a/tsdown.config.ts
+++ b/tsdown.config.ts
@@ -134,6 +134,7 @@ function buildCoreDistEntries(): Record<string, string> {
     "plugins/build-smoke-entry": "src/plugins/build-smoke-entry.ts",
     "plugins/runtime/index": "src/plugins/runtime/index.ts",
     "llm-slug-generator": "src/hooks/llm-slug-generator.ts",
+    "mcp/plugin-tools-serve": "src/mcp/plugin-tools-serve.ts",
   };
 }