Principle Migrate Callers Then Delete Legacy Apis

---
name: principle-migrate-callers-then-delete-legacy-apis
description: "Apply when replacing an internal API without leaving ambiguous dual paths."
license: MIT
metadata:
  author: jstack-maintainers
  source: michael-denyer/pstack-claude
  source-version: "0.9.30"
  source-commit: 45f768349a6d7d7e71509fee3f5bccfad54b3bad
  owner: software-factory
  risk: low
  capabilities: jstack,engineering-principle
user-invocable: false
---

# Migrate Callers Then Delete Legacy APIs

When we decide a new API is the right design, migrate callers and remove the old API in the same refactor wave instead of preserving compatibility layers.

**Rule:**
- Do not keep legacy API paths only because internal callers still exist
- Inventory callers, migrate them, and delete the old API immediately
- Treat temporary adapters as exceptional and time-boxed, not default architecture
- Update tests to assert the new contract, and delete tests that only protect pre-refactor implementation details

**When this applies:**
- No external users depend on backward compatibility
- The project can absorb coordinated breaking changes
- The new API is part of a simplification or refactor initiative

Keeping both old and new APIs creates dual-path complexity, slows cleanup, and makes the codebase feel append-only.