Probed at b7a68884: only the C# cache arm retypes a key (cache {A,B}
replaces B's record with A); cacheless writes already refuse. TS, Rust
and Python key records by (type, key), so two types coexist at one key
and no leaf has a retype path; leaf parity needs key identity first.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
