Struct PrefixFingerprint 

pub struct PrefixFingerprint {
    pub system_stable_hash: u64,
    pub system_knowledge_hash: u64,
    pub turn_hashes: Vec<u64>,
}

Per-render fingerprint of the cacheable prefix — the segments a provider caches as a stable prefix (system blocks + history turns). Excludes state_turn (the volatile uncached tail) and token_count metadata (not on the wire). This is the metrics-first instrument (P0-A) behind the optimization work: two renders share a reusable KV / prompt-cache prefix iff their system hashes match and one’s turn_hashes is a prefix of the other’s. Pure and derived — never stored in snapshots, session logs, or event logs.

Fields

system_stable_hash: u64

system_knowledge_hash: u64

turn_hashes: Vec<u64>

One stable hash per history turn, in order. The longest common prefix with a previous render’s vector = how many turns stay cache-reusable across the call.

Implementations

impl PrefixFingerprint

pub fn extends(&self, prev: &PrefixFingerprint) -> bool

True when self’s cacheable prefix is a byte-stable extension of prev: identical system segments and prev.turn_hashes is a prefix of self.turn_hashes. This is exactly the KV / prompt-cache reuse condition — no drift anywhere in the prefix, only growth at the tail.

pub fn common_turn_prefix(&self, prev: &PrefixFingerprint) -> usize

Number of leading turns byte-identical to prev — the reusable turn-prefix length. A drop below prev.turn_hashes.len() signals mid-prefix churn (a turn rewritten in place, e.g. an in-place collapse) that invalidates cache.

Trait Implementations

impl Clone for PrefixFingerprint

fn clone(&self) -> PrefixFingerprint

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PrefixFingerprint

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for PrefixFingerprint

impl PartialEq for PrefixFingerprint

fn eq(&self, other: &PrefixFingerprint) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for PrefixFingerprint