Bundle dependencies during transpile command

cli/build/transpile/index.ts

@@ -1,5 +1,6 @@
-import path from "node:path"
 import fs from "node:fs"
+import { builtinModules } from "node:module"
+import path from "node:path"
 import { rollup } from "rollup"
 import typescript from "@rollup/plugin-typescript"
 import resolve from "@rollup/plugin-node-resolve"
@@ -13,6 +14,19 @@ import {
   STATIC_ASSET_EXTENSIONS,
 } from "./static-asset-plugin"
 
+const isNodeBuiltin = (id: string) => {
+  const withoutNodePrefix = id.replace(/^node:/, "")
+
+  return (
+    builtinModules.includes(id) ||
+    builtinModules.includes(withoutNodePrefix) ||
+    builtinModules.includes(`node:${withoutNodePrefix}`)
+  )
+}
+
+const isTscircuitDependency = (id: string) =>
+  id === "tscircuit" || id.startsWith("tscircuit/")
+
 const createExternalFunction =
   (projectDir: string, tsconfigPath?: string) =>
   (id: string): boolean => {
@@ -71,8 +85,18 @@ const createExternalFunction =
       return false // This is a local file, don't externalize
     }
 
-    // Everything else (npm packages like 'react', 'tscircuit', etc.) is external
-    return true
+    // Keep Node.js built-ins external
+    if (isNodeBuiltin(id)) {
+      return true
+    }
+
+    // Always externalize tscircuit so it's not bundled with user output
+    if (isTscircuitDependency(id)) {
+      return true
+    }
+
+    // Bundle all other dependencies into the output
+    return false
   }
 
 export const transpileFile = async ({

tests/cli/transpile/transpile-dependencies.test.ts

@@ -0,0 +1,38 @@
+import { test, expect } from "bun:test"
+import { readFile, symlink, writeFile } from "node:fs/promises"
+import path from "node:path"
+import { getCliTestFixture } from "../../fixtures/get-cli-test-fixture"
+
+test("transpile bundles dependencies except for tscircuit", async () => {
+  const { tmpDir, runCommand } = await getCliTestFixture()
+  const circuitPath = path.join(tmpDir, "with-deps.ts")
+
+  await writeFile(
+    circuitPath,
+    `import kleur from "kleur"
+import * as tscircuit from "tscircuit"
+
+export const coloredText = kleur.red("ok")
+export const usesTscircuit = () =>
+  typeof tscircuit === "object" ? "tscircuit-present" : "missing"
+`,
+  )
+
+  await writeFile(path.join(tmpDir, "package.json"), "{}")
+
+  await symlink(
+    path.resolve(process.cwd(), "node_modules"),
+    path.join(tmpDir, "node_modules"),
+    "dir",
+  )
+
+  await runCommand(`tsci transpile ${circuitPath}`)
+
+  const esmPath = path.join(tmpDir, "dist", "index.js")
+  const esmContent = await readFile(esmPath, "utf-8")
+
+  expect(esmContent).toMatch(/from ['\"]tscircuit['\"]/)
+  expect(esmContent).not.toContain('from "kleur"')
+  expect(esmContent).not.toContain('require("kleur")')
+  expect(esmContent).toContain("tscircuit-present")
+}, 30_000)