fix(render): resolve a relative stylesheet root before comparing it

CHANGELOG.md

@@ -36,6 +36,8 @@ Semver applies from 1.0.0. A breaking change to a documented API needs a major 
   In an app whose default locale is not `en`, every tab read `⟦dev.panel.mail.title⟧`. The
   framework catalog is registered under `en` only, and the shell translated through the app's
   ambient locale.
+- **render:** `setStylesheetRoot` resolves a relative root, so `loadApp('.')` from `/app` classifies
+  sheets correctly. Found in review of #528.
 
 ## 22.2.1 - 2026-09-25
 

packages/render/src/module-loader.test.ts

@@ -265,6 +265,15 @@ describe('an app served from /app', () => {
     expect(site).not.toContain('color:blue');
   });
 
+  // `loadApp('.')` from `/app` names a RELATIVE root, and every path the plugin hands the loader is
+  // absolute: compared as written, the root matched nothing and the `/app/` segment won again.
+  test('a relative root is resolved against the working directory before it is compared', () => {
+    setStylesheetRoot('app');
+    const sheet = join(process.cwd(), 'app', 'apps/web/site/page.module.scss');
+    loadStylesheet(sheet, '.hero{color:red}');
+    expect(registeredStylesheets()[0]?.surface).toBe('site');
+  });
+
   // The order `x build` meets: a sheet can register before `loadApp` names the root, and a
   // classification frozen at registration would keep the answer the wrong root gave.
   test('naming the root reclassifies what registered before it, and moves the revision', () => {

packages/render/src/module-loader.ts

@@ -4,6 +4,9 @@
  * `bun test` all load a component the same way and there is no separate "bundled" behaviour.
  */
 
+// why: Bun ships no path API, and a relative app root has to be resolved against the working
+// directory before it can be compared with the absolute paths the Bun plugin hands this loader.
+import { resolve } from 'node:path';
 import { renderThrowable } from '@ultimat3/core';
 import { compileStylesheet, isGlobalStylesheet, stripCharset } from './css-modules';
 import { PrerenderFailedError } from './errors';
@@ -115,10 +118,12 @@ const surfaceOfSheet = (path: string): Surface | null =>
  * Every sheet already registered is classified again, because a sheet can load before the root is
  * named — and a classification frozen then would keep the answer the wrong root gave. The revision
  * moves only when an answer does, so naming the same root twice mints no new stylesheet URL.
- * `undefined` returns to the working directory.
+ * A relative root is resolved against the working directory. `undefined` returns to the working
+ * directory.
  */
 export function setStylesheetRoot(root: string | undefined): void {
-  stylesheetRoot = root;
+  // Resolved: `loadApp('.')` is a legal call, and `.` is a prefix of no absolute path.
+  stylesheetRoot = root === undefined ? undefined : resolve(root);
   for (const [path, sheet] of stylesheets) {
     const surface = surfaceOfSheet(path);
     if (surface === sheet.surface) continue;