migration-guidance

Update guidance when a v3 public module or API is renamed, moved, removed, replaced, or gains a materially different v4 contract. A v4-only API without a v3 counterpart does not automatically need an annotation.

1. Account for every affected v3 symbol.
2. Read annotations.md before adding or changing annotation YAML. Verify every suggested replacement against implementation and tests.
3. When checking or regenerating the reference, or when the API change exists in a committed ref, read generation.md. Otherwise report that generation is deferred.
4. When output was generated, inspect it for unrelated movement and stale refs.

The task is complete when every affected v3 symbol is accounted for, annotation replacements are verified, checks and generation succeed when the change is in a committed ref, and every generated difference is explained. Report deferred checks explicitly for uncommitted API changes.