fix: bundle prettier into dist by removing it from esbuild external list

__tests__/integration-bundled-binary.test.ts

@@ -0,0 +1,139 @@
+/**
+ * Integration test that validates the bundled dist/bin/index.js binary
+ * is self-contained and does not require external node_modules at runtime.
+ *
+ * REGRESSION TEST FOR: ERR_MODULE_NOT_FOUND: Cannot find package 'prettier'
+ *
+ * ROOT CAUSE:
+ * `prettier` was listed in the `external` array in scripts/esbuild.mjs, which
+ * excluded it from the bundle. When the action runs in a user's workflow, only
+ * `dist/` is present — there is no `node_modules/prettier` to resolve.
+ *
+ * THE FIX:
+ * Removed `prettier` from the `external` array so it gets bundled into
+ * dist/bin/index.js. Since prettier is a declared `dependency` (not
+ * devDependency) in package.json, bundling it is correct.
+ *
+ * WHAT THIS TEST VALIDATES:
+ * - The dist/bin/index.js binary runs successfully in an isolated temporary
+ *   directory that has no node_modules directory
+ * - No ERR_MODULE_NOT_FOUND error for 'prettier' or any other bundled dep
+ * - The binary produces valid README output when given a valid action.yml
+ */
+import { execSync } from 'node:child_process';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+describe('Integration Test - Bundled Binary Self-Containment', () => {
+  let tempDir: string;
+  const binaryPath = path.resolve(import.meta.dirname, '../dist/bin/index.js');
+
+  beforeEach(() => {
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gha-bundled-binary-test-'));
+  });
+
+  afterEach(() => {
+    if (tempDir && fs.existsSync(tempDir)) {
+      fs.rmSync(tempDir, { recursive: true, force: true });
+    }
+  });
+
+  it('dist/bin/index.js exists and is executable', () => {
+    expect(fs.existsSync(binaryPath), `dist/bin/index.js not found at ${binaryPath}`).toBe(true);
+    const stat = fs.statSync(binaryPath);
+    // Check that it's a file with non-zero size (bundled with prettier it should be >20MB)
+    expect(stat.size).toBeGreaterThan(1024 * 1024); // at least 1MB
+  });
+
+  it('binary runs without ERR_MODULE_NOT_FOUND for prettier when no node_modules present', () => {
+    // Set up a minimal action.yml and README.md in tempDir (no node_modules)
+    const actionYml = `name: Test Action
+description: A test action for bundled binary validation
+inputs:
+  my-input:
+    description: A test input
+    required: false
+    default: hello
+outputs:
+  my-output:
+    description: A test output
+runs:
+  using: node20
+  main: index.js
+`;
+    fs.writeFileSync(path.join(tempDir, 'action.yml'), actionYml);
+
+    const readmeMd = `# Test Action
+
+<!-- start title -->
+<!-- end title -->
+
+<!-- start description -->
+<!-- end description -->
+
+<!-- start usage -->
+<!-- end usage -->
+
+<!-- start inputs -->
+<!-- end inputs -->
+
+<!-- start outputs -->
+<!-- end outputs -->
+`;
+    const readmePath = path.join(tempDir, 'README.md');
+    fs.writeFileSync(readmePath, readmeMd);
+
+    // Copy the binary into tempDir so Node.js resolves modules from tempDir,
+    // not from the project root (which has node_modules/prettier). This accurately
+    // simulates the GitHub Actions runner where only dist/ is available without
+    // an adjacent node_modules directory.
+    const isolatedBinaryPath = path.join(tempDir, 'index.js');
+    fs.copyFileSync(binaryPath, isolatedBinaryPath);
+    fs.chmodSync(isolatedBinaryPath, 0o755);
+
+    // Confirm no node_modules are present in the isolated directory
+    expect(fs.existsSync(path.join(tempDir, 'node_modules'))).toBe(false);
+
+    // Run the binary from tempDir — no node_modules anywhere in the hierarchy above tempDir
+    let stderr = '';
+    let exitCode = 0;
+
+    try {
+      execSync(
+        `node "${isolatedBinaryPath}" --owner testowner --repo testrepo` +
+          ` --paths:action "${path.join(tempDir, 'action.yml')}"` +
+          ` --paths:readme "${readmePath}"`,
+        {
+          cwd: tempDir,
+          encoding: 'utf8',
+          env: {
+            ...process.env,
+            // Clear GitHub Actions env vars to avoid side effects
+            GITHUB_ACTIONS: undefined,
+            GITHUB_REPOSITORY: undefined,
+            INPUT_OWNER: undefined,
+            INPUT_REPO: undefined,
+          },
+        },
+      );
+    } catch (error: unknown) {
+      const execError = error as { stdout?: string; stderr?: string; status?: number };
+      stderr = execError.stderr ?? '';
+      exitCode = execError.status ?? 1;
+    }
+
+    // The binary must NOT fail with ERR_MODULE_NOT_FOUND for prettier
+    expect(stderr).not.toContain('ERR_MODULE_NOT_FOUND');
+    expect(stderr).not.toContain("Cannot find package 'prettier'");
+
+    // The binary should succeed (exit 0)
+    expect(exitCode, `stderr: ${stderr}`).toBe(0);
+
+    // The README should be updated with generated content
+    const generatedReadme = fs.readFileSync(readmePath, 'utf8');
+    expect(generatedReadme).toContain('testowner/testrepo');
+  });
+});