Function derive_kv_ns 

pub fn derive_kv_ns(
    model_fp: u64,
    layout: &GroupLayout,
    elem_bytes: u32,
    block_size: u32,
    head_dim: u32,
    client_salt: u64,
) -> NonZeroU64

2026-09-25: Derive the KV paging namespace: FNV-1a/64 over fixed-width [tag][8-byte LE] records. A change to the fields or their order must bump KV_NS_VERSION:

tag	field	tag	field	tag	field
0x00	KV_NS_VERSION	0x04	block_size	0x08	num_kv_heads
0x01	model_fp	0x05	head_dim	0x09	fs_block_size
0x02	KV_DOMAIN	0x06	num_layers	0x0a	group_stride
0x03	elem_bytes	0x07	num_blocks	0x0b	client_salt

model_fp is ModelFingerprint::derive_kv in metrale-model-engine: model type, quantization identity, METRALE_MODEL_ID and geometry. A hash of 0 is replaced by FNV_OFFSET.