/principle-migrate-callers-then-delete-legacy-apis

name: principle-migrate-callers-then-delete-legacy-apis
description: "Apply when introducing a new internal API while old callers still exist. Migrate callers and delete the old API in the same wave instead of preserving compatibility layers."
disable-model-invocation: true

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.