@@ -0,0 +1,119 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @noflow
+ */
+
+'use strict';
+
+const {execFileSync} = require('node:child_process');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+
+const SCRIPT =
+  require.resolve('../../sdks/hermes-engine/utils/replace_hermes_version.js');
+const VERSION = '0.0.0-test';
+const BINARY =
+  'destroot/Library/Frameworks/universal/hermesvm.xcframework/ios-arm64/hermesvm.framework/hermesvm';
+
+function writeFile(filePath, contents) {
+  fs.mkdirSync(path.dirname(filePath), {recursive: true});
+  fs.writeFileSync(filePath, contents);
+}
+
+describe('Hermes configuration replacement', () => {
+  let podsRoot;
+  let binary;
+  let marker;
+
+  beforeEach(() => {
+    podsRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-config-test-'));
+    binary = path.join(podsRoot, 'hermes-engine', BINARY);
+    marker = path.join(podsRoot, 'hermes-engine/.last_build_configuration');
+  });
+
+  afterEach(() => {
+    fs.rmSync(podsRoot, {recursive: true, force: true});
+  });
+
+  function buildTarball(configuration) {
+    const stage = path.join(podsRoot, 'stage');
+    writeFile(path.join(stage, BINARY), configuration);
+    const artifacts = path.join(podsRoot, 'hermes-engine-artifacts');
+    fs.mkdirSync(artifacts, {recursive: true});
+    execFileSync('tar', [
+      '-czf',
+      path.join(
+        artifacts,
+        `hermes-ios-${VERSION}-${configuration.toLowerCase()}.tar.gz`,
+      ),
+      '-C',
+      stage,
+      '.',
+    ]);
+  }
+
+  function runScript(configuration) {
+    // Match the podspec's build phase: run the CLI from the Pods directory.
+    execFileSync(
+      process.execPath,
+      [SCRIPT, '-c', configuration, '-r', VERSION, '-p', podsRoot],
+      {cwd: podsRoot, encoding: 'utf8'},
+    );
+  }
+
+  it.each([
+    ['Debug', 'Release'],
+    ['Release', 'Debug'],
+  ])('restores %s when the marker is missing and %s remains', (target, old) => {
+    writeFile(binary, old);
+    buildTarball(target);
+
+    runScript(target);
+
+    expect(fs.readFileSync(binary, 'utf8')).toBe(target);
+    expect(fs.readFileSync(marker, 'utf8')).toBe(target);
+  });
+
+  it.each(['Debug', 'Release'])(
+    'keeps a recorded %s configuration without requiring a tarball',
+    configuration => {
+      writeFile(binary, configuration);
+      writeFile(marker, configuration);
+
+      runScript(configuration);
+
+      expect(fs.readFileSync(binary, 'utf8')).toBe(configuration);
+      expect(fs.readFileSync(marker, 'utf8')).toBe(configuration);
+    },
+  );
+
+  it.each([
+    ['Debug', 'Release'],
+    ['Release', 'Debug'],
+  ])('switches to %s when %s is recorded', (target, old) => {
+    writeFile(binary, old);
+    writeFile(marker, old);
+    buildTarball(target);
+
+    runScript(target);
+
+    expect(fs.readFileSync(binary, 'utf8')).toBe(target);
+    expect(fs.readFileSync(marker, 'utf8')).toBe(target);
+  });
+
+  it('records Debug after restoring a fresh install with no marker', () => {
+    writeFile(binary, 'Debug');
+    buildTarball('Debug');
+
+    runScript('Debug');
+
+    expect(fs.readFileSync(binary, 'utf8')).toBe('Debug');
+    expect(fs.readFileSync(marker, 'utf8')).toBe('Debug');
+  });
+});
@@ -56,7 +56,8 @@ Pod::Spec.new do |spec|
   if HermesEngineSourceType::isPrebuilt(source_type) then
 
     spec.subspec 'Pre-built' do |ss|
-      ss.preserve_paths = ["destroot/bin/*"].concat(["**/*.{h,c,cpp}"])
+      # Keep the configuration marker when CocoaPods cleans an unchanged pod.
+      ss.preserve_paths = ["destroot/bin/*", ".last_build_configuration"].concat(["**/*.{h,c,cpp}"])
       ss.source_files = ["destroot/include/hermes/**/*.h", "destroot/include/jsi/hermes.h"]
       ss.header_mappings_dir = "destroot/include"
       ss.ios.vendored_frameworks = "destroot/Library/Frameworks/universal/hermesvm.xcframework"
 
@@ -42,14 +42,8 @@ function shouldReplaceHermesConfiguration(configuration) {
     }
   }
 
-  // Assumption: if there is no stored last build, we assume that it was build for debug.
-  if (!fileExists && configuration === 'Debug') {
-    console.log(
-      'No previous build detected, but Debug Configuration. No need to replace Hermes engine',
-    );
-    return false;
-  }
-
+  // The binary may outlive its marker, so a missing marker does not imply Debug.
+  // Restore the requested configuration instead of assuming what is installed.
   return true;
 }
Original file line number	Diff line number	Diff line change
`@@ -42,14 +42,8 @@ function shouldReplaceHermesConfiguration(configuration) {`
`42`	`42`	`}`
`43`	`43`	`}`
`44`	`44`
`45`		`- // Assumption: if there is no stored last build, we assume that it was build for debug.`
`46`		`- if (!fileExists && configuration === 'Debug') {`
`47`		`- console.log(`
`48`		`- 'No previous build detected, but Debug Configuration. No need to replace Hermes engine',`
`49`		`- );`
`50`		`- return false;`
`51`		`- }`
`52`		`-`
	`45`	`+ // The binary may outlive its marker, so a missing marker does not imply Debug.`
	`46`	`+ // Restore the requested configuration instead of assuming what is installed.`
`53`	`47`	`return true;`
`54`	`48`	`}`
`55`	`49`