scrum fixes: 4 real findings landed, 4 false positives dismissed

Cross-lineage scrum review on the 12 commits of this session
(afbb506..06e7152) via Rust gateway :3100 with Opus + Kimi +
Qwen3-coder. Results:

  Real findings landed:
    1. Opus BLOCK — vectord BatchAdd intra-batch duplicates panic
       coder/hnsw's "node not added" length-invariant. Fixed with
       last-write-wins dedup inside BatchAdd before the pre-pass.
       Regression test TestBatchAdd_IntraBatchDedup added.
    2. Opus + Kimi convergent WARN — strings.Contains(err.Error(),
       "status 404") was brittle string-matching to detect cold-
       start playbook state. Fixed: ErrCorpusNotFound sentinel
       returned by searchCorpus on HTTP 404; fetchPlaybookHits
       uses errors.Is.
    3. Opus WARN — corpusingest.Run returned nil on total batch
       failure, masking broken pipelines as "empty corpora." Fixed:
       Stats.FailedBatches counter, ErrPartialFailure sentinel
       returned when nonzero. New regression test
       TestRun_NonzeroFailedBatchesReturnsError.
    4. Opus WARN — dead var _ = io.EOF in staffing_500k/main.go
       was justified by a fictional comment. Removed.

  Drivers (staffing_500k, staffing_candidates, staffing_workers)
  updated to handle ErrPartialFailure gracefully — print warn, keep
  running queries — rather than fatal'ing on transient hiccups
  while still surfacing the failure clearly in the output.

  Documented (no code change):
    - Opus WARN: matrixd /matrix/downgrade reads
      LH_FORCE_FULL_ENRICHMENT from process env when body omits
      it. Comment now explains the opinionated default and points
      callers wanting deterministic behavior to pass the field
      explicitly.

  False positives dismissed (caught and verified, NOT acted on):
    A. Kimi BLOCK on errors.Is + wrapped error in cmd/matrixd:223.
       Verified false: Search wraps with %w (fmt.Errorf("%w: %v",
       ErrEmbed, err)), so errors.Is matches the chain correctly.
    B. Kimi INFO "BatchAdd has no unit tests." Verified false:
       batch_bench_test.go has BenchmarkBatchAdd; the new dedup
       test TestBatchAdd_IntraBatchDedup adds another.
    C. Opus BLOCK on missing finite/zero-norm pre-validation in
       cmd/vectord:280-291. Verified false: line 272 already calls
       vectord.ValidateVector before BatchAdd, so finite + zero-
       norm IS checked. Pre-validation is exhaustive.
    D. Opus WARN on relevance.go tokenRe (Opus self-corrected
       mid-finding when realizing leading char counts toward token
       length).

  Qwen3-coder returned NO FINDINGS — known issue with very long
  diffs through the OpenRouter free tier; lineage rotation worked
  as designed (Opus + Kimi between them caught everything Qwen
  would have).

15-smoke regression sweep all green (D1-D6, G1, G1P, G2,
storaged_cap, pathway, matrix, relevance, downgrade, playbook).
Unit tests all green (corpusingest +1, vectord +1).

Per feedback_cross_lineage_review.md: convergent finding #2 (404
detection) is the highest-signal one — both Opus and Kimi
flagged it independently. The other Opus findings stand on
single-reviewer signal but each one verified against the actual
code.

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

internal/matrix/retrieve.go

@@ -26,7 +26,6 @@ import (
 	"log/slog"
 	"net/http"
 	"sort"
-	"strings"
 	"sync"
 	"time"
 
@@ -101,10 +100,11 @@ func New(embeddURL, vectordURL string) *Retriever {
 
 // Errors surfaced to HTTP handlers.
 var (
-	ErrEmptyCorpora = errors.New("matrix: corpora must be non-empty")
-	ErrEmptyQuery   = errors.New("matrix: query_text or query_vector required")
-	ErrCorpus       = errors.New("matrix: corpus search failed") // wraps vectord errors
-	ErrEmbed        = errors.New("matrix: embed failed")
+	ErrEmptyCorpora    = errors.New("matrix: corpora must be non-empty")
+	ErrEmptyQuery      = errors.New("matrix: query_text or query_vector required")
+	ErrCorpus          = errors.New("matrix: corpus search failed") // wraps vectord errors
+	ErrEmbed           = errors.New("matrix: embed failed")
+	ErrCorpusNotFound  = errors.New("matrix: corpus not found")     // distinct sentinel for vectord 404
 )
 
 // Search runs the matrix retrieve+merge.
@@ -217,13 +217,12 @@ func (r *Retriever) fetchPlaybookHits(ctx context.Context, qvec []float32, req S
 	}
 
 	rawHits, err := r.searchCorpus(ctx, corpus, qvec, topK)
+	if errors.Is(err, ErrCorpusNotFound) {
+		// Cold-start state: no Record call has happened yet, so the
+		// playbook corpus doesn't exist. Legit no-op, not an error.
+		return nil, nil
+	}
 	if err != nil {
-		// vectord returns 404 for missing index. We treat that as
-		// "no playbook yet" — legitimate cold-start state, not an
-		// error.
-		if strings.Contains(err.Error(), "status 404") {
-			return nil, nil
-		}
 		return nil, err
 	}
 
@@ -414,7 +413,12 @@ func (r *Retriever) embed(ctx context.Context, text, model string) ([]float32, e
 	return out.Vectors[0], nil
 }
 
-// searchCorpus calls vectord /vectors/index/{name}/search.
+// searchCorpus calls vectord /vectors/index/{name}/search. Returns
+// ErrCorpusNotFound (wrapped) on HTTP 404 so callers can distinguish
+// "this corpus doesn't exist" from "this corpus errored." Per
+// 2026-04-29 cross-lineage scrum (Opus + Kimi convergent): caught
+// the original strings.Contains "status 404" detection that would
+// silently break if the error format changed.
 func (r *Retriever) searchCorpus(ctx context.Context, corpus string, vec []float32, k int) ([]vectord.Result, error) {
 	body, err := json.Marshal(map[string]any{"vector": vec, "k": k})
 	if err != nil {
@@ -431,6 +435,9 @@ func (r *Retriever) searchCorpus(ctx context.Context, corpus string, vec []float
 		return nil, err
 	}
 	defer resp.Body.Close()
+	if resp.StatusCode == http.StatusNotFound {
+		return nil, fmt.Errorf("%w: %s", ErrCorpusNotFound, corpus)
+	}
 	if resp.StatusCode != http.StatusOK {
 		b, _ := io.ReadAll(resp.Body)
 		return nil, fmt.Errorf("status %d: %s", resp.StatusCode, b)