fix: apply ESM .js extension fallback to tsconfig path alias resolution

gitnexus/src/core/ingestion/import-resolvers/standard.ts

@@ -72,6 +72,13 @@ export const resolveImportPath = (
         const resolved = tryResolveWithExtensions(rewritten, allFiles);
         if (resolved) return cache(resolved);
 
+        // ESM fallback: strip .js/.jsx/.mjs/.cjs and retry with TS equivalents
+        const strippedAlias = stripJsExtension(rewritten);
+        if (strippedAlias !== null) {
+          const esmResolved = tryResolveWithExtensions(strippedAlias, allFiles);
+          if (esmResolved) return cache(esmResolved);
+        }
+
         // Try suffix matching as fallback
         const parts = rewritten.split('/').filter(Boolean);
         const suffixResult = suffixResolve(parts, normalizedFileList, allFileList, index);
@@ -132,9 +139,6 @@ export const resolveImportPath = (
 
     // TypeScript ESM: imports use .js/.jsx/.mjs/.cjs but source files are
     // .ts/.tsx/.mts/.cts. Strip the JS-family extension and re-resolve.
-    // NOTE: This fallback only applies to relative imports. Path alias imports
-    // (e.g. @/utils.js via tsconfig paths) do not yet strip .js extensions —
-    // that is a known limitation tracked for follow-up.
     if (language === SupportedLanguages.TypeScript || language === SupportedLanguages.JavaScript) {
       const stripped = stripJsExtension(basePath);
       if (stripped !== null) {

gitnexus/test/unit/esm-extension-resolution.test.ts

@@ -151,3 +151,76 @@ describe('stripJsExtension', () => {
   it('returns null for .ts', () => expect(stripJsExtension('foo/bar.ts')).toBeNull());
   it('returns null for no extension', () => expect(stripJsExtension('foo/bar')).toBeNull());
 });
+
+describe('ESM extension resolution — path aliases with .js extensions', () => {
+  const aliasAtToSrc = new Map<string, string>([['@/', 'src/']]);
+  const aliasTildeToSrc = new Map<string, string>([['~/', 'src/']]);
+
+  function resolveWithAlias(
+    currentFile: string,
+    importPath: string,
+    ctx: ReturnType<typeof makeCtx>,
+    aliases: Map<string, string>,
+    baseUrl = '.',
+  ): string | null {
+    return resolveImportPath(
+      currentFile,
+      importPath,
+      ctx.allFilesSet,
+      ctx.files,
+      ctx.normalized,
+      ctx.cache,
+      SupportedLanguages.TypeScript,
+      { aliases, baseUrl },
+      ctx.index,
+    );
+  }
+
+  it('resolves @/utils.js to src/utils.ts via alias', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/utils.ts']);
+    const result = resolveWithAlias('src/index.ts', '@/utils.js', ctx, aliasAtToSrc, '.');
+    expect(result).toBe('src/utils.ts');
+  });
+
+  it('resolves @/component.jsx to src/component.tsx via alias', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/component.tsx']);
+    const result = resolveWithAlias('src/index.ts', '@/component.jsx', ctx, aliasAtToSrc, '.');
+    expect(result).toBe('src/component.tsx');
+  });
+
+  it('resolves @/config.mjs to src/config.mts via alias', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/config.mts']);
+    const result = resolveWithAlias('src/index.ts', '@/config.mjs', ctx, aliasAtToSrc, '.');
+    expect(result).toBe('src/config.mts');
+  });
+
+  it('resolves @/legacy.cjs to src/legacy.cts via alias', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/legacy.cts']);
+    const result = resolveWithAlias('src/index.ts', '@/legacy.cjs', ctx, aliasAtToSrc, '.');
+    expect(result).toBe('src/legacy.cts');
+  });
+
+  it('prefers actual .js file over TS fallback in alias resolution', () => {
+    const ctx = makeCtx(['src/index.ts', 'src/utils.js', 'src/utils.ts']);
+    const result = resolveWithAlias('src/index.ts', '@/utils.js', ctx, aliasAtToSrc, '.');
+    expect(result).toBe('src/utils.js');
+  });
+
+  it('resolves alias with baseUrl prefix', () => {
+    const ctx = makeCtx(['app/src/index.ts', 'app/src/helpers/token.ts']);
+    const result = resolveWithAlias(
+      'app/src/index.ts',
+      '~/helpers/token.js',
+      ctx,
+      aliasTildeToSrc,
+      'app',
+    );
+    expect(result).toBe('app/src/helpers/token.ts');
+  });
+
+  it('returns null when alias .js import has no matching source', () => {
+    const ctx = makeCtx(['src/index.ts']);
+    const result = resolveWithAlias('src/index.ts', '@/missing.js', ctx, aliasAtToSrc, '.');
+    expect(result).toBeNull();
+  });
+});