Struct CacheSnapshot 

pub struct CacheSnapshot {
    pub kv_len: Vec<Option<usize>>,
    pub conv: Vec<Option<CudaSlice<f32>>>,
    pub ssm: Vec<Option<CudaSlice<f32>>>,
    pub pos: usize,
}

Snapshot of the dual cache taken BEFORE a spec-decode draft+verify round (MTP-PLAN §C/§D.4).

• Full-attn KV: only the per-layer len is recorded; rollback truncates (append-only, position-addressed — no copy). C.1.
• Linear-attn conv/ssm: real device-to-device COPIES of the recurrent state, because those buffers are mutated IN PLACE by the verify pass and have no position index to truncate. C.2. (CudaSlice::clone is an Arc refcount, NOT a buffer copy — so we alloc fresh + memcpy_dtod.)

Fields

kv_len: Vec<Option<usize>>

conv: Vec<Option<CudaSlice<f32>>>

ssm: Vec<Option<CudaSlice<f32>>>

pos: usize