fix: validate explicit project config filenames

Author: cursoragent

scripts/__tests__/rslib-harness.test.mjs

@@ -655,6 +655,39 @@ export default {
   });
 });
 
+test('resolveProjects rejects unsupported explicit project config files', async () => {
+  await withTempDir(async (root) => {
+    writeRslibProject(root, 'packages/pkg-a', 'pkg-a');
+    writeFile(
+      join(root, 'packages/pkg-a/custom.config.ts'),
+      'export default {};\n',
+    );
+    writeFile(
+      join(root, 'rslib.harness.config.mjs'),
+      `
+export default {
+  projects: [
+    {
+      root: './packages/pkg-a',
+      config: './custom.config.ts',
+    },
+  ],
+};
+`,
+    );
+
+    await assert.rejects(
+      () =>
+        resolveProjects({
+          harnessConfigPath: join(root, 'rslib.harness.config.mjs'),
+          rootDir: root,
+          projectFilters: [],
+        }),
+      /is not a supported rslib\.config\.\* file/,
+    );
+  });
+});
+
 test('validateCommandGuards rejects multi-project watch/mf-dev mode', () => {
   assert.throws(
     () =>

scripts/rslib-harness.mjs

@@ -731,6 +731,12 @@ async function resolveProjects({ harnessConfigPath, rootDir, projectFilters }) {
       );
     }
 
+    if (!isRslibConfigFile(explicitConfigFile)) {
+      throw new Error(
+        `Project config path "${explicitConfigFile}" is not a supported rslib.config.* file (from ${sourceConfig}).`,
+      );
+    }
+
     await addProject({
       name: entry.name,
       projectRoot: dirname(explicitConfigFile),