test(meta): ban no-factory vi.mock of virtual modules

A vi.mock('$app/navigation') with no factory does not auto-resolve to a
__mocks__ file for SvelteKit virtual modules — it substitutes some
exports and leaves others (replaceState) bound to the live router, which
is exactly the PR #657 failure. This Node-mode source scan, mirroring
no-async-mock-factories and no-duplicate-mock-ids, fails at every vitest
invocation if any *.svelte.{spec,test}.ts reintroduces the pattern, and
forecloses ADR-012's rejected Option C. Part of #560.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/__meta__/no-factory-ban.test.ts

@@ -0,0 +1,85 @@
+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 no-factory vi.mock anti-pattern named in
+// ADR-012 (the PR #657 failure class). A `vi.mock('$app/navigation')` with no
+// factory does NOT auto-resolve to an adjacent __mocks__ file the way Jest's
+// __mocks__/ does: for SvelteKit virtual modules, vitest substitutes some
+// exports (plain function refs like goto) but leaves others bound to the live
+// implementation (replaceState, which delegates through a getter). The result
+// is a partial mock that crashes when an unsubstituted export is hit.
+//
+// The sanctioned dedup pattern keeps the factory and shares its body:
+//   import * as formsMock from '$mocks/$app/forms';
+//   vi.mock('$app/forms', () => ({ ...formsMock }));
+//
+// ESLint and the CI grep guard catch the pattern earlier; this in-suite test
+// catches it at every vitest invocation — the layer hardest to disable. It
+// also forecloses ADR-012's rejected Option C (config-level auto-resolve).
+//
+// We scan source text rather than parsing AST: fast, no parser dependency,
+// good enough for the named anti-pattern. The pattern matches a `vi.mock`
+// call whose only argument is a string literal (no factory after a comma).
+
+const NO_FACTORY_VI_MOCK = /vi\.mock\(\s*['"][^'"]+['"]\s*\)/;
+
+export function hasNoFactoryViMock(source: string): boolean {
+	return NO_FACTORY_VI_MOCK.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: hasNoFactoryViMock', () => {
+	it('flags a vi.mock with a string id and no factory', () => {
+		expect(hasNoFactoryViMock(`vi.mock('$app/navigation');`)).toBe(true);
+	});
+
+	it('flags a no-factory vi.mock written across multiple lines', () => {
+		const fixture = `vi.mock(
+			'$app/forms'
+		);`;
+		expect(hasNoFactoryViMock(fixture)).toBe(true);
+	});
+
+	it('does not flag a vi.mock with an inline factory', () => {
+		expect(hasNoFactoryViMock(`vi.mock('$app/forms', () => ({ enhance: () => () => {} }));`)).toBe(
+			false
+		);
+	});
+
+	it('does not flag a vi.mock with a shared-body spread factory', () => {
+		const fixture = `import * as formsMock from '$mocks/$app/forms';
+			vi.mock('$app/forms', () => ({ ...formsMock }));`;
+		expect(hasNoFactoryViMock(fixture)).toBe(false);
+	});
+
+	it('does not flag a vi.mock with a named factory reference', () => {
+		expect(hasNoFactoryViMock(`vi.mock('$app/state', factory);`)).toBe(false);
+	});
+
+	it('does not flag source with no vi.mock at all', () => {
+		expect(hasNoFactoryViMock(`const x = vi.fn();`)).toBe(false);
+	});
+});
+
+describe('browser specs: no no-factory vi.mock of a virtual module', () => {
+	it('every src/**/*.svelte.{test,spec}.ts file keeps its factory', () => {
+		const specFiles = findBrowserSpecs();
+		expect(specFiles.length).toBeGreaterThan(0);
+		const offenders = specFiles.filter((file) => hasNoFactoryViMock(readFileSync(file, 'utf-8')));
+		expect(offenders).toEqual([]);
+	});
+});