test(meta): scan src/**/*.svelte.{test,spec}.ts for async vi.mock factories

In-suite belt-and-braces detector for the birpc teardown race named in
ADR-012 / #553. Catches `vi.mock(<arg>, async ... { ... await import(...)
... })` in any browser spec on every vitest invocation — the layer hardest
to disable or scope around (ESLint can be silenced; CI grep runs only in
CI; this test runs whenever the suite runs).

Demonstrated red→green by planting a synthetic offender locally and
watching the live-scan assertion fail; removing the offender returned it
to green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/__meta__/no-async-mock-factories.test.ts

@@ -0,0 +1,82 @@
+import { describe, it, expect } from 'vitest';
+import { readdirSync, readFileSync } from 'fs';
+import path from 'path';
+import { fileURLToPath } from 'url';
+
+// Belt-and-braces detector for the birpc teardown race named in ADR-012 / #553.
+// ESLint catches the pattern at save time, CI grep catches it before the test
+// suite launches, and this in-suite test catches it at every vitest invocation —
+// the layer hardest to disable or scope around.
+//
+// We scan source text rather than parsing AST: fast, no parser dependency,
+// good enough for the named anti-pattern. The pattern matches
+// `vi.mock(<arg>, async ... { ... await import(...) ... })`.
+
+const ASYNC_MOCK_WITH_DYNAMIC_IMPORT = /vi\.mock\([^)]*,\s*async[^{]*\{[\s\S]*?await\s+import\s*\(/;
+
+export function hasAsyncMockFactoryWithDynamicImport(source: string): boolean {
+	return ASYNC_MOCK_WITH_DYNAMIC_IMPORT.test(source);
+}
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const SRC_ROOT = path.resolve(__dirname, '..');
+
+function findBrowserSpecs(): string[] {
+	const entries = readdirSync(SRC_ROOT, { recursive: true, withFileTypes: true });
+	return entries
+		.filter(
+			(e) =>
+				e.isFile() && (e.name.endsWith('.svelte.test.ts') || e.name.endsWith('.svelte.spec.ts'))
+		)
+		.map((e) => path.join(e.parentPath ?? (e as { path: string }).path, e.name));
+}
+
+describe('scan: hasAsyncMockFactoryWithDynamicImport', () => {
+	it('flags async vi.mock factory with await import in body', () => {
+		const fixture = `vi.mock('$app/stores', async () => {
+			const mod = await import('./__mocks__/navigatingStore');
+			return { navigating: mod.navigatingStore };
+		});`;
+		expect(hasAsyncMockFactoryWithDynamicImport(fixture)).toBe(true);
+	});
+
+	it('does not flag sync vi.mock factory', () => {
+		const fixture = `vi.mock('$app/state', () => ({ navigating: { type: null } }));`;
+		expect(hasAsyncMockFactoryWithDynamicImport(fixture)).toBe(false);
+	});
+
+	it('does not flag async vi.mock factory without dynamic import', () => {
+		const fixture = `vi.mock('foo', async () => {
+			const x = await Promise.resolve(42);
+			return { bar: x };
+		});`;
+		expect(hasAsyncMockFactoryWithDynamicImport(fixture)).toBe(false);
+	});
+
+	it('does not flag dynamic import outside any vi.mock', () => {
+		const fixture = `async function load() {
+			const mod = await import('./something');
+			return mod.default;
+		}`;
+		expect(hasAsyncMockFactoryWithDynamicImport(fixture)).toBe(false);
+	});
+
+	it('flags async factory written as async function expression', () => {
+		const fixture = `vi.mock('foo', async function () {
+			const mod = await import('./bar');
+			return mod;
+		});`;
+		expect(hasAsyncMockFactoryWithDynamicImport(fixture)).toBe(true);
+	});
+});
+
+describe('browser specs: no async vi.mock factory contains await import', () => {
+	it('every src/**/*.svelte.{test,spec}.ts file is clean', () => {
+		const specFiles = findBrowserSpecs();
+		expect(specFiles.length).toBeGreaterThan(0);
+		const offenders = specFiles.filter((file) =>
+			hasAsyncMockFactoryWithDynamicImport(readFileSync(file, 'utf-8'))
+		);
+		expect(offenders).toEqual([]);
+	});
+});