retrieval

name	retrieval
description	This skill should be used when modifying api/internal/retrieval/ (query, streaming answers, chunk hydration), or when asked "how does retrieval work", "why re-filter after Qdrant already filtered", "add a new caller of loadChunks", "why does Retrieve query Postgres full-text too". Documents four non-obvious invariants in the retrieval pipeline that look redundant or arbitrary but aren't.

Retrieval pipeline invariants

Defense-in-depth workspace filtering

Retrieve re-filters Qdrant results by chunk.WorkspaceID == req.WorkspaceID in Go, even though the Qdrant query already filters by the workspace_id payload field server-side (and lexicalSearch's SQL already scopes by workspace_id too). This is documented defense-in-depth, not redundant code to delete — it protects against a payload/query mismatch bug or a future change to either filter silently leaking cross-workspace chunks. Keep all filters if touching this path.

Hydration order is not query order

Postgres chunk hydration (WHERE id = ANY($1)) does not preserve Qdrant's ranked order — SQL gives no ordering guarantee for ANY(). The code re-sorts hydrated rows using a fused score map (see below) built from the original candidate lists' order. Any new caller of loadChunks must apply its own re-sort — reusing the raw hydration result directly will silently return chunks in the wrong relevance order.

topK is clamped, not validated

topK silently clamps to [1, 50] rather than returning an error for out-of-range input. If a caller needs to know whether their requested topK was honored as-is, they must compare the request value to the response themselves — the retrieval layer won't tell them it was clamped.

Retrieve fuses vector search with Postgres full-text search

Retrieve is not pure vector search: it also runs lexicalSearch, a Postgres full-text query against the generated chunks.content_tsv column ('simple' text-search config — deliberately no stemming, since the goal is catching literal technical terms regardless of query language, not English grammar). Both the Qdrant vector search and lexicalSearch are widened to a candidatePoolSize(topK) pool (wider than the final topK), then combined via Reciprocal Rank Fusion (rrfK = 60) before truncating to topK. This exists because pure cosine similarity systematically under-ranks structurally "dense" content (tables, diagrams) relative to short generic prose, even when the dense content literally contains the query's terms — confirmed empirically before this was added. RetrievedChunk.Score still reports the chunk's vector cosine similarity (0 if it was a lexical-only match), not the RRF fusion score — RRF is an internal ranking signal on a different, much smaller scale, not something to surface as a citation "confidence" number.