diff --git a/frontend/eslint.config.js b/frontend/eslint.config.js
index a56c710b..88aa8a53 100644
--- a/frontend/eslint.config.js
+++ b/frontend/eslint.config.js
@@ -82,6 +82,17 @@ export default defineConfig(
 						"CallExpression[callee.object.name='vi'][callee.property.name='mock'] > Literal[value=/^pdfjs-dist/]",
 					message:
 						"Banned: vi.mock('pdfjs-dist', factory) causes a birpc teardown race in browser-mode specs — see ADR 012. Use the libLoader prop injection pattern instead."
+				},
+				{
+					// ADR 012 / #553. The named mechanism: an async vi.mock factory whose
+					// body performs `await import(...)` produces a late birpc roundtrip
+					// during worker teardown. The factory body must be synchronous; if
+					// you need to share state between the spec and the mock, use
+					// `vi.hoisted` (see DropZone.svelte.spec.ts).
+					selector:
+						"CallExpression[callee.object.name='vi'][callee.property.name='mock'][arguments.1.type='ArrowFunctionExpression'][arguments.1.async=true]:has(AwaitExpression > ImportExpression)",
+					message:
+						'Banned: vi.mock(..., async () => { await import(...) }) causes a birpc teardown race in browser-mode specs — see ADR 012. Use a synchronous factory + vi.hoisted instead.'
 				}
 			]
 		}