diff --git a/.github/workflows/coding-standards.yml b/.github/workflows/coding-standards.yml
index bd260800ca..67c41200b5 100644
--- a/.github/workflows/coding-standards.yml
+++ b/.github/workflows/coding-standards.yml
@@ -55,6 +55,7 @@ jobs:
   # - Logs PHP_CodeSniffer debug information.
   # - Runs PHPCS on the full codebase with warnings suppressed.
   # - Runs PHPCS on the `tests` directory without warnings suppressed.
+  # - Ensures version-controlled files are not modified or deleted.
   # - todo: Configure Slack notifications for failing scans.
   phpcs:
     name: PHP coding standards
@@ -94,6 +95,9 @@ jobs:
       - name: Check test suite files for warnings
         run: phpcs tests -q --report=checkstyle | cs2pr
 
+      - name: Ensure version-controlled files are not modified during the tests
+        run: git diff --exit-code
+
   # Runs the JavaScript coding standards checks.
   #
   # JSHint violations are not currently reported inline with annotations.
@@ -105,6 +109,7 @@ jobs:
   # - Logs updated debug information.
   # _ Installs NPM dependencies using install-changed to hash the `package.json` file.
   # - Run the WordPress JSHint checks.
+  # - Ensures version-controlled files are not modified or deleted.
   # - todo: Configure Slack notifications for failing tests.
   jshint:
     name: JavaScript coding standards
@@ -140,3 +145,6 @@ jobs:
 
       - name: Run JSHint
         run: npm run grunt jshint
+
+      - name: Ensure version-controlled files are not modified or deleted
+        run: git diff --exit-code
diff --git a/.github/workflows/end-to-end-tests.yml b/.github/workflows/end-to-end-tests.yml
index c3f1f09ecf..12b6355641 100644
--- a/.github/workflows/end-to-end-tests.yml
+++ b/.github/workflows/end-to-end-tests.yml
@@ -45,6 +45,7 @@ jobs:
   # - Logs Docker debug information (about both the Docker installation within the runner and the WordPress container).
   # - Install WordPress within the Docker container.
   # - Run the E2E tests.
+  # - Ensures version-controlled files are not modified or deleted.
   # - todo: Configure Slack notifications for failing tests.
   e2e-tests:
     name: E2E Tests
@@ -113,3 +114,6 @@ jobs:
 
       - name: Run E2E tests
         run: npm run test:e2e
+
+      - name: Ensure version-controlled files are not modified or deleted
+        run: git diff --exit-code
diff --git a/.github/workflows/javascript-tests.yml b/.github/workflows/javascript-tests.yml
index d5ad21c0e7..06eb81bd19 100644
--- a/.github/workflows/javascript-tests.yml
+++ b/.github/workflows/javascript-tests.yml
@@ -49,6 +49,7 @@ jobs:
   # - Logs updated debug information.
   # _ Installs NPM dependencies using install-changed to hash the `package.json` file.
   # - Run the WordPress QUnit tests.
+  # - Ensures version-controlled files are not modified or deleted.
   # - todo: Configure Slack notifications for failing tests.
   test-js:
     name: QUnit Tests
@@ -82,3 +83,6 @@ jobs:
 
       - name: Run QUnit tests
         run: npm run grunt qunit:compiled
+
+      - name: Ensure version-controlled files are not modified or deleted
+        run: git diff --exit-code
diff --git a/.github/workflows/php-compatibility.yml b/.github/workflows/php-compatibility.yml
index b7c35fdd9f..cb6409d954 100644
--- a/.github/workflows/php-compatibility.yml
+++ b/.github/workflows/php-compatibility.yml
@@ -49,6 +49,7 @@ jobs:
   # - Make Composer packages available globally.
   # - Logs PHP_CodeSniffer debug information.
   # - Runs the PHP compatibility tests.
+  # - Ensures version-controlled files are not modified or deleted.
   # - todo: Configure Slack notifications for failing scans.
   php-comatibility:
     name: Check PHP compatibility
@@ -84,3 +85,6 @@ jobs:
 
       - name: Run PHP compatibility tests
         run: phpcs --standard=phpcompat.xml.dist -q --report=checkstyle | cs2pr
+
+      - name: Ensure version-controlled files are not modified or deleted
+        run: git diff --exit-code
diff --git a/.github/workflows/phpunit-tests.yml b/.github/workflows/phpunit-tests.yml
index f57316fcb9..2f29086f72 100644
--- a/.github/workflows/phpunit-tests.yml
+++ b/.github/workflows/phpunit-tests.yml
@@ -55,6 +55,7 @@ jobs:
   # - Logs debug information about what's installed within the WordPress Docker containers.
   # - Install WordPress within the Docker container.
   # - Run the PHPUnit tests.
+  # - Ensures version-controlled files are not modified or deleted.
   # - Checks out the WordPress Test reporter repository.
   # - Reconnect the directory to the Git repository.
   # - Submit the test results to the WordPress.org host test results.
@@ -221,6 +222,9 @@ jobs:
         if: ${{ ! matrix.split_slow }}
         run: LOCAL_PHP_XDEBUG=true npm run test:${{ env.PHPUNIT_SCRIPT }} -- -v --group xdebug --exclude-group __fakegroup__
 
+      - name: Ensure version-controlled files are not modified or deleted
+        run: git diff --exit-code
+
       - name: Checkout the WordPress Test Reporter
         if: ${{ github.repository == 'WordPress/wordpress-develop' && github.ref == 'refs/heads/master' && matrix.report }}
         uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f # v2.3.4
diff --git a/.github/workflows/test-coverage.yml b/.github/workflows/test-coverage.yml
index 67a53c4a0b..e82fa1e1e4 100644
--- a/.github/workflows/test-coverage.yml
+++ b/.github/workflows/test-coverage.yml
@@ -43,8 +43,10 @@ jobs:
   # - Logs debug information about what's installed within the WordPress Docker containers.
   # - Install WordPress within the Docker container.
   # - Run the PHPUnit tests as a single site.
+  # - Ensures version-controlled files are not modified or deleted.
   # - Upload the single site code coverage report to Codecov.io.
   # - Run the PHPUnit tests as a multisite.
+  # - Ensures version-controlled files are not modified or deleted.
   # - Upload the multisite code coverage report to Codecov.io.
   test-coverage-report:
     name: ${{ matrix.multisite && 'Multisite' || 'Single site' }} report
@@ -121,6 +123,9 @@ jobs:
         if: ${{ ! matrix.multisite }}
         run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c phpunit.xml.dist --coverage-clover wp-code-coverage-single-clover-${{ github.sha }}.xml
 
+      - name: Ensure version-controlled files are not modified during the tests
+        run: git diff --exit-code
+
       - name: Upload single site report to Codecov
         if: ${{ ! matrix.multisite }}
         uses: codecov/codecov-action@e156083f13aff6830c92fc5faa23505779fbf649 # v1.2.1
@@ -132,6 +137,9 @@ jobs:
         if: ${{ matrix.multisite }}
         run: npm run test:${{ env.PHPUNIT_SCRIPT }} -- --verbose -c tests/phpunit/multisite.xml --coverage-clover wp-code-coverage-multisite-clover-${{ github.sha }}.xml
 
+      - name: Ensure version-controlled files are not modified during the tests
+        run: git diff --exit-code
+
       - name: Upload multisite report to Codecov
         if: ${{ matrix.multisite }}
         uses: codecov/codecov-action@e156083f13aff6830c92fc5faa23505779fbf649 # v1.2.1
diff --git a/.github/workflows/test-npm.yml b/.github/workflows/test-npm.yml
index c806e13c55..3774ee2851 100644
--- a/.github/workflows/test-npm.yml
+++ b/.github/workflows/test-npm.yml
@@ -45,8 +45,10 @@ jobs:
   # _ Installs NPM dependencies using install-changed to hash the `package.json` file.
   # - Builds WordPress to run from the `build` directory.
   # - Cleans up after building WordPress to the `build` directory.
+  # - Ensures version-controlled files are not modified or deleted.
   # - Builds WordPress to run from the `src` directory.
   # - Cleans up after building WordPress to the `src` directory.
+  # - Ensures version-controlled files are not modified or deleted.
   test-npm:
     name: Test NPM on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
@@ -83,12 +85,18 @@ jobs:
       - name: Clean after building
         run: npm run grunt clean
 
+      - name: Ensure version-controlled files are not modified or deleted during building and cleaning
+        run: git diff --exit-code
+
       - name: Build WordPress in /src
         run: npm run build:dev
 
       - name: Clean after building in /src
         run: npm run grunt clean -- --dev
 
+      - name: Ensure version-controlled files are not modified or deleted during building and cleaning
+        run: git diff --exit-code
+
   # Verifies that installing NPM dependencies and building WordPress works as expected on MacOS.
   #
   # This is a separate job in order to that more strict conditions can be used.
@@ -100,8 +108,10 @@ jobs:
   # _ Installs NPM dependencies using install-changed to hash the `package.json` file.
   # - Builds WordPress to run from the `build` directory.
   # - Cleans up after building WordPress to the `build` directory.
+  # - Ensures version-controlled files are not modified or deleted.
   # - Builds WordPress to run from the `src` directory.
   # - Cleans up after building WordPress to the `src` directory.
+  # - Ensures version-controlled files are not modified or deleted.
   test-npm-macos:
     name: Test NPM on MacOS
     runs-on: macos-latest
@@ -133,8 +143,14 @@ jobs:
       - name: Clean after building
         run: npm run grunt clean
 
+      - name: Ensure version-controlled files are not modified or deleted during building and cleaning
+        run: git diff --exit-code
+
       - name: Build WordPress in /src
         run: npm run build:dev
 
       - name: Clean after building in /src
         run: npm run grunt clean -- --dev
+
+      - name: Ensure version-controlled files are not modified or deleted during building and cleaning
+        run: git diff --exit-code
diff --git a/.github/workflows/test-old-branches.yml b/.github/workflows/test-old-branches.yml
index 2bb5664a98..3478439a42 100644
--- a/.github/workflows/test-old-branches.yml
+++ b/.github/workflows/test-old-branches.yml
@@ -69,3 +69,6 @@ jobs:
               workflow_id: '${{ matrix.workflow }}',
               ref: '${{ matrix.branch }}'
             });
+
+      - name: Ensure version-controlled files are not modified during the tests
+        run: git diff --exit-code
diff --git a/Gruntfile.js b/Gruntfile.js
index a24e701e06..349328d145 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -122,7 +122,8 @@ module.exports = function(grunt) {
 				WORKING_DIR + 'wp-includes/js/'
 			],
 			'webpack-assets': [
-				WORKING_DIR + 'wp-includes/assets/'
+				WORKING_DIR + 'wp-includes/assets/*',
+				'!' + WORKING_DIR + 'wp-includes/assets/script-loader-packages.php'
 			],
 			dynamic: {
 				dot: true,