poimen-memory/tasks/M8.3-query-optimizer.md

M8.3 — Query optimizer: context construction + strategy routing

Field	Value
Phase	M8 — Hybrid Search
Size	M — 1–2 days
Status	✅ COMPLETE
Flags	—
Spec	inlined below
Blocks	M8.5
Depends	— (pure logic, no infra dependency)

Goal

Build a QueryOptimizer that analyses a raw user query and produces a QueryContext — normalised text, extracted entities, classified question type, and a routed SearchStrategy. This runs before any database call and determines which engines to use.

Design

6-stage pipeline:

1. Normalize — lowercase, trim, collapse whitespace.
2. Tokenize — split on whitespace.
3. Extract entities — detect years (YYYY), quoted phrases ("exact"), tags (#, @).
4. Analyse characteristics — boolean flags: has_special_syntax, has_date_filters, has_negation.
5. Classify question type — one of: Factual, Procedural, Comparative, Troubleshooting, Navigational, Open.
6. Route — pick SearchStrategy with a confidence score (0.0–1.0).

Routing rules:

• Token count < 3 → LexicalOnly (BM25 handles keywords better than embeddings).
• Special syntax (#tag, @mention, "phrase") → LexicalOnly (preserve exact tokens).
• Date filters present → LexicalFirst (narrow by date in OpenSearch, rerank in pgvector).
• Procedural / Troubleshooting → Hybrid (need both exact errors + semantic understanding).
• Navigational → LexicalFirst (finding specific docs).
• Default → Hybrid.

Output struct:

pub struct QueryContext {
    pub raw_query: String,
    pub normalized_query: String,
    pub tokens: Vec<String>,
    pub entities: HashMap<String, String>,
    pub embedding: Option<Vec<f32>>,  // filled later by worker
    pub token_count: usize,
    pub has_special_syntax: bool,
    pub has_date_filters: bool,
    pub has_negation: bool,
    pub question_type: QuestionType,
    pub search_strategy: SearchStrategy,
    pub confidence: f32,
}

Steps

1. Implement QueryOptimizer with optimize_query(&str) -> Result<QueryContext>.
2. Implement each stage as a private method.
3. Write unit tests for every routing rule (≥15 tests).
4. No async, no IO, no dependencies beyond std. Pure logic.

Acceptance

1. optimize_query("fix port") → LexicalOnly, confidence ≥ 0.7.
2. optimize_query("How do I fix kubernetes port 8080?") → Hybrid, Procedural, confidence ≥ 0.9.
3. optimize_query("#networking @devops policy") → LexicalOnly, has_special_syntax=true.
4. optimize_query("deployment failures in 2024") → LexicalFirst, has_date_filters=true, entity year=2024.
5. optimize_query("Compare Docker and Kubernetes") → Hybrid, Comparative.
6. All 15+ tests pass.

Verify

cargo test -p mem-cli query_optimizer:: -- --nocapture

False pass: Routing always returns Hybrid regardless of input. Check the short-query and special-syntax tests specifically — they must return non-Hybrid strategies.

Artifacts

• crates/mem-cli/src/query_optimizer.rs (exists, needs cleanup + test fixes)