fix: remove raw write re-exports from facade (cache bypass)

PR-Agent #1150 review flagged that re-exporting
saveUnifiedConfig/mutateUnifiedConfig/updateUnifiedConfig
allows callers to bypass the cache. Only export the
cache-coherent wrappers (saveConfig/mutateConfig/updateConfig).
Raw functions still available via direct import from
unified-config-loader if needed.

- Remove raw write re-exports from facade
- Add test verifying raw writes are NOT exported
- Add test verifying cache-coherent wrappers ARE exported

src/config/__tests__/config-loader-facade.test.ts

@@ -63,9 +63,6 @@ describe('config-loader-facade', () => {
 
       expect(typeof facade.loadUnifiedConfig).toBe('function');
       expect(typeof facade.loadOrCreateUnifiedConfig).toBe('function');
-      expect(typeof facade.saveUnifiedConfig).toBe('function');
-      expect(typeof facade.mutateUnifiedConfig).toBe('function');
-      expect(typeof facade.updateUnifiedConfig).toBe('function');
     });
 
     it('should export all path/format utilities', async () => {
@@ -115,6 +112,24 @@ describe('config-loader-facade', () => {
     });
   });
 
+  describe('cache coherence', () => {
+    it('should NOT export raw write functions that bypass cache', async () => {
+      const facade = (await importFacade()) as Record<string, unknown>;
+
+      expect(facade.saveUnifiedConfig).toBeUndefined();
+      expect(facade.mutateUnifiedConfig).toBeUndefined();
+      expect(facade.updateUnifiedConfig).toBeUndefined();
+    });
+
+    it('should export cache-coherent write wrappers instead', async () => {
+      const facade = await importFacade();
+
+      expect(typeof facade.saveConfig).toBe('function');
+      expect(typeof facade.mutateConfig).toBe('function');
+      expect(typeof facade.updateConfig).toBe('function');
+    });
+  });
+
   describe('memoization', () => {
     it('getCachedConfig returns equivalent config on repeated calls', async () => {
       const facade = await importFacade();

src/config/config-loader-facade.ts

@@ -2,21 +2,23 @@
  * Config Loader Facade
  *
  * Single import path for all config loading operations.
- * Re-exports everything from unified-config-loader and config-manager,
- * and adds memoization for loadOrCreateUnifiedConfig to reduce file I/O.
+ * Re-exports read-only functions from unified-config-loader and config-manager,
+ * and provides cache-coherent write wrappers that keep the memoization cache in sync.
+ *
+ * IMPORTANT: Raw write functions (saveUnifiedConfig, mutateUnifiedConfig,
+ * updateUnifiedConfig) are NOT re-exported here. Use the cache-coherent
+ * wrappers (saveConfig, mutateConfig, updateConfig) instead. If you need
+ * the raw functions, import directly from './unified-config-loader'.
  *
  * Usage:
  *   import { getCachedConfig, saveConfig, mutateConfig } from '../config/config-loader-facade';
  *   import { getCcsDir, loadSettings } from '../config/config-loader-facade';
  */
 
-// Re-export all functions from unified-config-loader
+// Re-export read-only functions from unified-config-loader
 export {
   loadUnifiedConfig,
   loadOrCreateUnifiedConfig,
-  saveUnifiedConfig,
-  mutateUnifiedConfig,
-  updateUnifiedConfig,
   getConfigYamlPath,
   getConfigJsonPath,
   hasUnifiedConfig,