| Concern | When Present in Core | When Isolated | Notes |
|---|---|---|---|
| State tangled | Deep session + global state | Event-based boundary | Controlled interaction |
| Business logic coupled | Theme-level cart mutation | Contract-driven events | Behavioural isolation |
| Schema drift | Implicit payload structure | Versioned event surface | Deterministic integration |
| Network dependency | Global cart API calls | Explicit integration | Transparent behaviour |
| CSS bleed | Header layout dependency | Scoped styling | Safer header changes |