Phase 28-36 body of work

Accumulated since a6f12e2 (Phase 21 Rust port + Phase 27 versioning):

- Phase 36: embed_semaphore on VectorState (permits=1) serializes
  seed embed calls — prevents sidecar socket collisions under
  concurrent /seed stress load
- Phase 31+: run_stress.ts 6-task diverse stress scaffolding;
  run_e2e_rated.ts + orchestrator.ts tightening
- Catalog dedupe cleanup: 16 duplicate manifests removed; canonical
  candidates.parquet (10.5MB -> 76KB) + placements.parquet (1.2MB ->
  11KB) regenerated post-dedupe; fresh manifests for active datasets
- vectord: harness EvalSet refinements (+181), agent portfolio
  rotation + ingest triggers (+158), autotune + rag adjustments
- catalogd/storaged/ingestd/mcp-server: misc tightening
- docs: Phase 28-36 PRD entries + DECISIONS ADR additions;
  control-plane pivot banner added to top of docs/PRD.md (pointing
  at docs/CONTROL_PLANE_PRD.md which lands in next commit)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/vectord-lance/src/lib.rs

@@ -357,7 +357,25 @@ impl LanceVectorStore {
     /// Search for top_k nearest neighbors of `query`. Uses the IVF_PQ
     /// index if one exists; otherwise does a full scan (slow but
     /// correct — useful during development before index build).
-    pub async fn search(&self, query: &[f32], top_k: usize) -> Result<Vec<Hit>, String> {
+    ///
+    /// `nprobes` tells Lance how many IVF partitions to probe per query.
+    /// Lance's built-in default is **1**, which caps recall well below
+    /// what the index is actually capable of. Passing `None` keeps that
+    /// default (only sensible when latency trumps recall); for real
+    /// workloads set `nprobes` to 5–10% of `num_partitions` (e.g. 20–30
+    /// on a 316-partition index).
+    ///
+    /// `refine_factor` re-ranks the PQ-approximate top-k by computing
+    /// exact distances on `top_k * refine_factor` candidates, then
+    /// trimming to `top_k`. Cheap way to buy back recall lost to product
+    /// quantization. `None` skips the re-rank pass.
+    pub async fn search(
+        &self,
+        query: &[f32],
+        top_k: usize,
+        nprobes: Option<usize>,
+        refine_factor: Option<u32>,
+    ) -> Result<Vec<Hit>, String> {
         use lance::dataset::Dataset;
 
         let dataset = Dataset::open(&self.path).await.map_err(e)?;
@@ -365,6 +383,8 @@ impl LanceVectorStore {
 
         let mut scanner = dataset.scan();
         scanner.nearest("vector", &qarr, top_k as usize).map_err(e)?;
+        if let Some(n) = nprobes { scanner.nprobes(n); }
+        if let Some(f) = refine_factor { scanner.refine(f); }
         scanner.project(&["doc_id", "chunk_text"]).map_err(e)?;
 
         let mut stream = scanner.try_into_stream().await.map_err(e)?;