Struct MidchunkCapture 

pub struct MidchunkCapture<'a> {
    pub cap_local: usize,
    pub h_dsts: &'a [DevicePtr],
    pub conv_dsts: &'a [DevicePtr],
    pub h_bytes: usize,
    pub conv_bytes: usize,
    pub ssm_layer_counter: &'a AtomicUsize,
    pub cap_local_early: Option<usize>,
    pub h_dsts_early: &'a [DevicePtr],
    pub conv_dsts_early: &'a [DevicePtr],
    pub replay_tail: bool,
}

2026-09-25: Per-pass descriptor for mid-chunk SSM tail capture: the reserved snapshot slot’s per-SSM-layer destinations and the split point in pass-local token coordinates.

Each SSM layer’s prefill takes one ordinal from ssm_layer_counter, in model order, and uses it to index h_dsts/conv_dsts.

Fields

cap_local: usize

2026-09-25: Capture the state after this many tokens of the pass (tb - proc_start).

h_dsts: &'a [DevicePtr]

2026-09-25: Per-SSM-layer h_state destination in the reserved slot.

conv_dsts: &'a [DevicePtr]

2026-09-25: Per-SSM-layer conv_state destination in the reserved slot.

h_bytes: usize

2026-09-25: Bytes per layer of h_state.

conv_bytes: usize

2026-09-25: Bytes per layer of conv_state.

ssm_layer_counter: &'a AtomicUsize

2026-09-25: Per-pass SSM-layer ordinal counter, starting at 0.

cap_local_early: Option<usize>

2026-09-25: Split point of a second capture one KV block earlier, at tb - block_size; Some only when the pass covers that point and a second snapshot slot was reserved.

h_dsts_early: &'a [DevicePtr]

2026-09-25: Per-SSM-layer h_state destination in the tb - block_size slot.

conv_dsts_early: &'a [DevicePtr]

2026-09-25: Per-SSM-layer conv_state destination in the tb - block_size slot.

replay_tail: bool

2026-10-01: The rows from cap_local on must get the bits a prefill pass starting at cap_local would give them, the pass a later request runs when it restores the captured state (a tail-split capture, prefill_plan::tail_split_point): the GDN recurrence after the split takes the exact-replay arm, and attention runs those rows as their own paged call. False for the metrale_scale tail capture.