Struct SpecSession 

pub struct SpecSession {
    pub committed: Vec<u32>,
    pub next_pred: Option<u32>,
    pub sctr: u32,
    pub uctr: u32,
    pub pending_tok: Option<u32>,
    pub telem: SpecTelemetry,
    /* private fields */
}

Fields

committed: Vec<u32>

Every token whose state the caches hold, in order (prompt turns + generated), INCLUDING overshoot: spec commits accepted drafts past max_new; those rows are in the caches, so the session must count them. Callers render output from this, not from their own echo.

next_pred: Option<u32>

Greedy argmax predicting the token AFTER committed.last() (from the last turn’s final logits). Fuels empty-suffix continuation bursts (serve): the next turn emits this token first, feeds it, and the round loop resumes without any prime. None before the first turn.

sctr: u32

SAMPLED-SPEC stream continuity across bursts: Philox event counters persist here so a session’s randomness never repeats between generate_spec_session calls. (0,0) at admit.

uctr: u32

pending_tok: Option<u32>

PENDING-CARRY across bursts (2026-08-01, the serve burst-boundary fix): the bonus token emitted by the last round but NOT committed to the caches. The old tail committed it with a solo T=1 trunk pass (+ draft fill), and the next burst’s setup fed the stashed next_pred with ANOTHER solo pass — 2x ~11.5ms/burst measured on H100 q27 ([spec-setup] trace). Carrying it lets the next empty-suffix greedy burst consume it as round-0 verify col 0, exactly like a mid-burst full-accept boundary (no solo passes). INVARIANT: when set, committed (== cache rows) EXCLUDES this token although it was already emitted in the last burst’s output, and last_h holds the hidden of the last COMMITTED row (its predecessor — the chain-seed/fill anchor). next_pred is None (unknown without the commit pass). Non-empty-suffix or sampled turns must flush first (spec_flush_pending); generate_spec_session_sampled does this at entry, and serve parks only flushed sessions.

telem: SpecTelemetry

Session-lifetime acceptance telemetry (lane/accept-telemetry). Host-side u64 adds at the round accounting the loop already does — no syncs, no allocation. NOTE a pool-resumed session carries the PREVIOUS requests’ counts; per-request consumers diff with SpecTelemetry::delta_since around each burst.

Implementations

impl SpecSession

pub fn cache_max_ctx(&self) -> usize

Context capacity of the session’s caches (the server’s ContextFull guard).

pub fn rewind_pos(&self) -> Option<usize>

Committed position this session can REWIND to (its retained prompt-end boundary), if any. A request whose prompt matches committed[..pos] exactly can resume from here — see spec_rewind_to_checkpoint.