# ABI compatibility query (K1236–K1240)

`negotiate` performs one read-only kernel version query before the caller
acquires or starts an image. It accepts only supported required/available
versions under the separate runtime ABI contract. A V1 client on a V1 kernel
receives a `Session`. A V2-required image on a V1 kernel receives
`Unsupported { required: 2, available: 1 }`; callers must stop before
acquisition. Wire and kernel failures are separate errors.

`NativeProbe` is available only for AArch64 `target_os = "none"` and issues
the frozen V1 Version0 call. The host tests use a counting probe. K1240 must
verify a real EL0 startup path and unchanged ownership after incompatibility.