Interface Requirements
Interfaces define how the system connects to external systems, APIs, services, and user-facing endpoints. Answer: What does the system connect to?
UID prefix: INTF- Traces up to: Features (FEAT-) Implemented by: API clients and adapters (# impl INTF-NNN) Verified by: Integration tests (# verify INTF-NNN)
The system shall integrate with [external system] to [purpose].
Direction: [inbound / outbound / bidirectional] Protocol: [REST / GraphQL / SMTP / webhook / file transfer] Authentication: [API key / OAuth / certificate] Data exchanged: [what flows in/out] Frequency: [real-time / batch / on-demand] Fallback behavior: [what happens when unavailable]