Struct RerankSpec 

pub struct RerankSpec {
    pub enabled: bool,
    pub rerank_k: u32,
    pub model: String,
    pub passage_field: String,
    pub signal_blend: f32,
    pub query_text: String,
    pub validate_only: bool,
}

─── Second-stage reranking (optional) ───────────────────────────────────────

First-class, optional second-stage reranker over an over-fetched candidate window for plain VectorSearch / HybridSearch. Mirrors Weaviate reranker modules, Pinecone’s rerank API, Vespa global-phase rank-profiles, and Cohere/Qdrant rerank: a stateless, bounded, post-merge stage run once globally after shard fan-in. Additive & wire-compatible — old clients omit this message ⇒ rerank off, behavior identical to today.

Fields

enabled: bool

master switch (false / message-absent ⇒ no rerank)

rerank_k: u32

over-fetch pool size; 0 ⇒ default max(k*4, 24) clamped to the mode’s hard cap (48 for cross-encoder; 200 for the cheaper maxsim late-interaction path, sized for the issue’s “top-K ~100-200” fused window).

model: String

“cross-encoder” | “maxsim” | “learned” | “score-fusion” | “custom”; “” ⇒ “score-fusion”.

• “maxsim” — token-level ColBERT-style MaxSim late interaction: the query and each hydrated passage are encoded into per-token L2-normalized matrices and scored Σ_q max_d q·d ÷ query-token-count. LLM-free; needs the embedding model loaded + query_text + passage_field, else it degrades to score-fusion (never errors).
• “learned” — (#768 LongMemEval Phase 7) non-generative GBDT reranker over the funnel feature vector [dense, BM25, MaxSim, recency, graph-distance, granularity], trained on LongMemEval dev relevance labels. Applied as the FINAL rerank over the fused+reranked candidate set. Needs a model loaded (STATELET_LEARNED_RERANKER_MODEL); else degrades to score-fusion. LLM-free.

passage_field: String

KV-key template for passage hydration (cross-encoder / maxsim). Tokens: {id} → candidate vector/result id (decimal) {index} → index_name e.g. “doc:{index}:{id}:text”. Empty ⇒ hydration disabled ⇒ fall back to score-fusion.

signal_blend: f32

score-fusion only: blend = blend*norm_distance + (1-blend)*aux_signal. 0 ⇒ default 1.0 (pure full-precision/coarse distance re-rank). Range [0,1].

query_text: String

Raw query text for the text-based rerankers (both RPCs query by vector, not text). Required for model=“cross-encoder” and model=“maxsim”; empty ⇒ auto-downgrade to score-fusion.

validate_only: bool

Dry-run pre-flight validation. When true the RPC validates the rerank spec (passage_field template via validate_passage_field, plus reranker availability for model=“cross-encoder”) and returns an empty successful response if valid, or an InvalidArgument/FailedPrecondition Status if not — without executing the search. SDKs expose it as rerank_validate(…). Additive & wire-compatible: old clients omit it ⇒ false ⇒ unchanged.

Trait Implementations

impl Clone for RerankSpec

fn clone(&self) -> RerankSpec

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for RerankSpec

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

Formats the value using the given formatter.

impl Default for RerankSpec

fn default() -> Self

Returns the “default value” for a type.

impl Message for RerankSpec

fn encoded_len(&self) -> usize

Returns the encoded length of the message without a length delimiter.

fn clear(&mut self)

Clears the message, resetting all fields to their default.

fn encode(&self, buf: &mut impl BufMut) -> Result<(), EncodeError>

where Self: Sized,

Encodes the message to a buffer.

fn encode_to_vec(&self) -> Vec<u8>

where Self: Sized,

Encodes the message to a newly allocated buffer.

fn encode_length_delimited( &self, buf: &mut impl BufMut, ) -> Result<(), EncodeError>

where Self: Sized,

Encodes the message with a length-delimiter to a buffer.

fn encode_length_delimited_to_vec(&self) -> Vec<u8>

where Self: Sized,

Encodes the message with a length-delimiter to a newly allocated buffer.

fn decode(buf: impl Buf) -> Result<Self, DecodeError>

where Self: Default,

Decodes an instance of the message from a buffer.

fn decode_length_delimited(buf: impl Buf) -> Result<Self, DecodeError>

where Self: Default,

Decodes a length-delimited instance of the message from the buffer.

fn merge(&mut self, buf: impl Buf) -> Result<(), DecodeError>

where Self: Sized,

Decodes an instance of the message from a buffer, and merges it into self.

fn merge_length_delimited(&mut self, buf: impl Buf) -> Result<(), DecodeError>

where Self: Sized,

Decodes a length-delimited instance of the message from buffer, and merges it into self.

impl PartialEq for RerankSpec

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for RerankSpec