diff --git a/scripts/hooks/config-protection.js b/scripts/hooks/config-protection.js
index 9250ee5b8..6e9350d4d 100644
--- a/scripts/hooks/config-protection.js
+++ b/scripts/hooks/config-protection.js
@@ -93,6 +93,40 @@ const PROTECTED_FILES = new Set([
   '.markdownlintignore'
 ]);
 
+/**
+ * Exact basenames only catch a tool's canonical entry point. Real repos split
+ * flat config across files: a shared `eslint.config.base.mjs` holding the
+ * ignore list and rule severities, imported by per-workspace
+ * `eslint.config.mjs` files. That is the common monorepo shape, and matching
+ * basenames alone protected the leaves while leaving the trunk -- the file that
+ * actually carries the rules -- freely editable.
+ *
+ * These patterns cover `<tool>.config.<qualifier>.<ext>` and
+ * `.<tool>rc.<qualifier>.<ext>` for the linters and formatters listed above.
+ * They are case-insensitive for the same reason the Set lookup above is.
+ *
+ * Deliberately NOT matched: build and test tooling -- `vite.config.ts`,
+ * `vitest.config.ts`, `jest.config.js`, `playwright.config.ts`,
+ * `tsconfig.json`. This hook exists to stop a LINTER config being weakened in
+ * place of fixing the code; editing a bundler or test-runner config is
+ * ordinary work, and sweeping those in would make the hook obstructive.
+ */
+const PROTECTED_PATTERNS = [
+  // eslint.config.base.mjs, prettier.config.shared.cjs, stylelint.config.local.js ...
+  /^(eslint|prettier|stylelint|commitlint|oxlint|biome)\.config(\.[A-Za-z0-9_-]+)*\.(js|mjs|cjs|ts|mts|cts)$/i,
+  // .eslintrc.base.json, .prettierrc.shared.yml ...
+  /^\.(eslintrc|prettierrc|stylelintrc|markdownlintrc)(\.[A-Za-z0-9_-]+)*\.(js|cjs|mjs|json|jsonc|yml|yaml|toml)$/i,
+  // biome.base.json, biome.shared.jsonc
+  /^biome(\.[A-Za-z0-9_-]+)*\.jsonc?$/i,
+];
+
+function isProtectedName(basename) {
+  const lower = basename.toLowerCase();
+  return PROTECTED_FILES.has(basename)
+    || PROTECTED_FILES.has(lower)
+    || PROTECTED_PATTERNS.some((re) => re.test(basename));
+}
+
 function parseInput(inputOrRaw) {
   if (typeof inputOrRaw === 'string') {
     try {
@@ -132,7 +166,7 @@ function run(inputOrRaw, options = {}) {
   // silently overwrite the real config while the guard returned exit 0.
   // On genuinely case-sensitive filesystems this only costs a false positive
   // on a distinct file that differs from a protected name by case alone.
-  if (PROTECTED_FILES.has(basename) || PROTECTED_FILES.has(basename.toLowerCase())) {
+  if (isProtectedName(basename)) {
     // Allow first-time creation — there's no existing config to weaken.
     // The hook's purpose is blocking modifications; writing a brand-new
     // config file in a project that has none is a legitimate bootstrap
diff --git a/tests/hooks/config-protection.test.js b/tests/hooks/config-protection.test.js
index 787fbd346..2ebedd6e7 100644
--- a/tests/hooks/config-protection.test.js
+++ b/tests/hooks/config-protection.test.js
@@ -418,6 +418,64 @@ function runTests() {
     })
   );
 
+  results.push(
+    test('blocks shared/base flat configs, not just the canonical entry point', () => {
+      // Monorepos split flat config: a shared `eslint.config.base.mjs` holding
+      // the ignore list and rule severities, imported by per-workspace
+      // `eslint.config.mjs` files. Matching basenames alone protected the
+      // leaves and left the trunk -- the file that carries the rules -- editable.
+      return withOwnedDirectory(fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-config-protect-base-')), tmpDir => {
+        const names = [
+          'eslint.config.base.mjs', 'prettier.config.shared.cjs', '.eslintrc.base.json', 'ESLint.Config.Base.MJS',
+          'stylelint.config.local.ts', 'commitlint.config.shared.cts', 'oxlint.config.base.mts',
+          'biome.config.shared.js', '.prettierrc.shared.yml', '.stylelintrc.team.toml',
+          '.markdownlintrc.team.jsonc', 'biome.shared.jsonc', 'BIOME.Team.Base.JSON'
+        ];
+        for (const name of names) {
+          const absPath = path.join(tmpDir, name);
+          fs.writeFileSync(absPath, '{}');
+
+          const result = runHook({ tool_name: 'Edit', tool_input: { file_path: absPath } });
+
+          assert.strictEqual(result.code, 2, 'Expected ' + name + ' to be blocked');
+          assert.ok(
+            result.stderr.includes('BLOCKED: Modifying ' + name + ' is not allowed.'),
+            'Expected block message for ' + name + ', got: ' + result.stderr
+          );
+        }
+      });
+    })
+  );
+
+  results.push(
+    test('does not block build or test tooling configs', () => {
+      // Pins the boundary: this hook guards LINTER configs. A future widening
+      // of the patterns must not quietly start blocking ordinary work.
+      return withOwnedDirectory(fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-config-protect-allow-')), tmpDir => {
+        const names = [
+          'vite.config.ts', 'vitest.config.ts', 'jest.config.js', 'playwright.config.ts', 'tsconfig.json',
+          'pyproject.toml', 'package.json', '.eslintignore.bak', 'not-eslint.config.base.mjs',
+          'eslint.config..mjs', 'eslint.config.base.mjs.bak'
+        ];
+        for (const name of names) {
+          const absPath = path.join(tmpDir, name);
+          fs.writeFileSync(absPath, '{}');
+
+          const result = runHook({ tool_name: 'Edit', tool_input: { file_path: absPath } });
+
+          assert.strictEqual(result.code, 0, 'Expected ' + name + ' to be allowed, stderr: ' + result.stderr);
+        }
+
+        const fresh = runHook({
+          tool_name: 'Write',
+          tool_input: { file_path: path.join(tmpDir, 'eslint.config.new.mjs'), content: 'export default [];' }
+        });
+        assert.strictEqual(fresh.code, 0, 'Expected first-time qualified config creation to be allowed');
+        assert.strictEqual(fresh.stdout, '', 'Allowed qualified creation should not echo raw hook input');
+      });
+    })
+  );
+
   const passed = results.filter(result => result === 'passed').length;
   const failed = results.filter(result => result === 'failed').length;
   const skipped = results.filter(result => result === 'skipped').length;