BMAD-METHOD/src/bmm-skills/3-solutioning/bmad-architecture/references/interface-design.md

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# Interface Design for Refinement
Use this reference only when interface shape is a material architecture decision.
## Produce alternatives
Compare at least three realistic shapes:
1. Minimal — the smallest stable behavior callers need.
2. Flexible — justified variation without leaking implementation detail.
3. Caller-optimized — shaped around the dominant caller workflow.
Add a ports-and-adapters option only when at least two real implementations or a true external dependency justify the seam.
For each option show:
- interface shape and brief caller usage
- behavior, state, and dependencies hidden behind it
- ownership and dependency direction
- adapter strategy, if any
- observable test surface
- migration and rollback cost
- compatibility or conflict with existing `AD` IDs
## Decide
Rank the options by divergence prevented, locality of change and knowledge, interface leverage, migration risk, and altitude fit. Recommend one option or a precise hybrid; do not leave an unranked menu.
The recommendation becomes architecture only after it is accepted or ratified by existing reality and recorded in the memlog. The resulting spine `AD` states the enforceable rule; detailed examples and rejected alternatives remain in the companion or memlog.