From 41dca5d0c760489528b6f82b0e62154729bb5990 Mon Sep 17 00:00:00 2001
From: kazuya kawaguchi <kawakazu80@gmail.com>
Date: Wed, 18 Mar 2026 15:45:26 +0900
Subject: [PATCH 1/2] fix(core): copy esm-shims.js to dist during tsdown
 bundling

resolve #999
---
 .../core/__tests__/build-artifacts.spec.ts    | 19 +++++++++++++++++++
 packages/core/build.ts                        |  8 ++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 packages/core/__tests__/build-artifacts.spec.ts

diff --git a/packages/core/__tests__/build-artifacts.spec.ts b/packages/core/__tests__/build-artifacts.spec.ts
new file mode 100644
index 0000000000..995ad5edb8
--- /dev/null
+++ b/packages/core/__tests__/build-artifacts.spec.ts
@@ -0,0 +1,19 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import url from 'node:url';
+
+import { describe, expect, it } from 'vitest';
+
+const coreDir = path.resolve(path.dirname(url.fileURLToPath(import.meta.url)), '..');
+const distDir = path.join(coreDir, 'dist');
+
+describe('build artifacts', () => {
+  it('should include esm-shims.js in dist for tsdown shims support', () => {
+    const shimsPath = path.join(distDir, 'esm-shims.js');
+    expect(fs.existsSync(shimsPath), `${shimsPath} should exist`).toBe(true);
+
+    const content = fs.readFileSync(shimsPath, 'utf8');
+    expect(content).toContain('__dirname');
+    expect(content).toContain('__filename');
+  });
+});
diff --git a/packages/core/build.ts b/packages/core/build.ts
index 3bc80533f7..29d5b4a376 100644
--- a/packages/core/build.ts
+++ b/packages/core/build.ts
@@ -428,6 +428,14 @@ async function bundleTsdown() {
       }),
     ],
   });
+
+  // Copy esm-shims.js to dist/ so tsdown's shims option can resolve it.
+  // tsdown resolves this file via path.resolve(import.meta.dirname, '..', 'esm-shims.js'),
+  // which means it expects the file at dist/esm-shims.js (one level up from dist/tsdown/).
+  await copyFile(
+    join(tsdownSourceDir, 'esm-shims.js'),
+    join(projectDir, 'dist/esm-shims.js'),
+  );
 }
 
 async function brandTsdown() {

From 1fecdf05cfd2dbf84bffec948138320136928624 Mon Sep 17 00:00:00 2001
From: kazuya kawaguchi <kawakazu80@gmail.com>
Date: Wed, 18 Mar 2026 16:25:00 +0900
Subject: [PATCH 2/2] chore(core): format

---
 packages/core/build.ts | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/core/build.ts b/packages/core/build.ts
index 29d5b4a376..d375eafd03 100644
--- a/packages/core/build.ts
+++ b/packages/core/build.ts
@@ -432,10 +432,7 @@ async function bundleTsdown() {
   // Copy esm-shims.js to dist/ so tsdown's shims option can resolve it.
   // tsdown resolves this file via path.resolve(import.meta.dirname, '..', 'esm-shims.js'),
   // which means it expects the file at dist/esm-shims.js (one level up from dist/tsdown/).
-  await copyFile(
-    join(tsdownSourceDir, 'esm-shims.js'),
-    join(projectDir, 'dist/esm-shims.js'),
-  );
+  await copyFile(join(tsdownSourceDir, 'esm-shims.js'), join(projectDir, 'dist/esm-shims.js'));
 }
 
 async function brandTsdown() {