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>

cmd/matrixd/main.go

@@ -143,8 +143,14 @@ func (h *handlers) handlePlaybookRecord(w http.ResponseWriter, r *http.Request)
 }
 
 // downgradeRequest is the POST /matrix/downgrade body. Mirrors
-// matrix.DowngradeInput; ForceFullOverride is read from the
-// LH_FORCE_FULL_ENRICHMENT env var when omitted from the body.
+// matrix.DowngradeInput. When ForceFullOverride is omitted from
+// the body, the value falls back to matrixd's process env
+// (LH_FORCE_FULL_ENRICHMENT) — an opinionated default that lets
+// operators set the env var on the matrixd unit and have every
+// gate decision honor it without per-request changes. Per
+// 2026-04-29 cross-lineage scrum (Opus WARN): callers that want
+// deterministic gate behavior independent of matrixd's env should
+// pass ForceFullOverride explicitly in the body.
 type downgradeRequest struct {
 	Mode              string `json:"mode"`
 	Model             string `json:"model"`