refactor(core): centralize path validation and allow temp dir access for tools (#17185)

Co-authored-by: Your Name <joshualitt@google.com>

integration-tests/ripgrep-real.test.ts

@@ -31,6 +31,10 @@ class MockConfig {
   getFileFilteringRespectGeminiIgnore() {
     return true;
   }
+
+  validatePathAccess() {
+    return null;
+  }
 }
 
 describe('ripgrep-real-direct', () => {