fix: address greptile P2 review comments

- Cache defaultCodeExtensions at module level in isCodeFile so callers
  that pass no pre-built set avoid a per-call Set allocation
- Add motivation comment to scripts/run-vitest.mjs explaining why the
  wrapper exists instead of invoking vitest directly
- Always assign runtimeOverrides in applyServerConfig even when empty,
  so stale overrides don't persist if config hints are later removed

Author: PatrickSys

scripts/run-vitest.mjs

@@ -1,3 +1,5 @@
+// Spawns vitest via process.execPath to avoid bin-resolution failures when
+// Node is invoked directly (e.g. `node scripts/run-vitest.mjs`) without pnpm.
 import { spawn } from 'node:child_process';
 import { fileURLToPath } from 'node:url';
 

src/index.ts

@@ -1667,10 +1667,8 @@ async function applyServerConfig(
       configRoots.set(rootKey, { rootPath: proj.root });
       registerKnownRoot(proj.root);
       const runtimeOverrides = buildProjectRuntimeOverrides(proj);
-      if (Object.keys(runtimeOverrides).length > 0) {
-        const project = getOrCreateProject(proj.root);
-        project.runtimeOverrides = runtimeOverrides;
-      }
+      const project = getOrCreateProject(proj.root);
+      project.runtimeOverrides = runtimeOverrides;
     } catch {
       console.error(`[config] Skipping inaccessible project root: ${proj.root}`);
     }

src/utils/language-detection.ts

@@ -176,6 +176,9 @@ function buildCodeExtensions(extraExtensions?: Iterable<string>): Set<string> {
   return merged;
 }
 
+// Cached default set — built once at module load, reused by callers that pass no extra extensions.
+const defaultCodeExtensions: ReadonlySet<string> = buildCodeExtensions();
+
 /**
  * Detect language from file path
  */
@@ -193,7 +196,11 @@ export function isCodeFile(
 ): boolean {
   const ext = path.extname(filePath).toLowerCase();
   const supportedExtensions =
-    extensions instanceof Set ? extensions : buildCodeExtensions(extensions);
+    extensions instanceof Set
+      ? extensions
+      : extensions
+        ? buildCodeExtensions(extensions)
+        : defaultCodeExtensions;
   return supportedExtensions.has(ext);
 }