- Create tests/e2e/lib/helpers.ts with shared SSE mock functions
- Add proper error UI assertions to error-handling.spec.ts
- Remove waitForTimeout calls in favor of real assertions
- Update 6 test files to use shared helpers
- Add tests for generate, edit, and append diagram operations
- Use SSE mocked responses matching AI SDK UI message stream format
- Generate mxCell XML directly in tests for deterministic assertions
- Tests verify tool card rendering and 'Complete' badge state