scrum 2026-05-02: materializer+replay+vectord — ship-with-fixes

Cross-lineage review of 89ca72d (Opus + Kimi + Qwen3-coder).

Convergent findings (≥2 reviewers): NONE.

- Kimi BLOCK (materializer main.go exits 0 on validation fail):
  confabulation. Code does os.Exit(1) at lines 65-66.
- Qwen BLOCK (saveTask race condition): confabulation. All access
  to inflight/pending is under s.mu.
- Qwen WARN (saveAfter nil deref): confabulation. Explicit
  `if h.persist == nil { return }` guard at line 184.
- Opus BLOCK (TestSaveTask_Coalesces): self-withdrawn in same
  response.

Opus WARNs actioned:
- Detached docstring on TestAdd_SmallIndex_ConcurrentDistinctIDs —
  attached.
- isoDatePartition fallback comment — clarified as defense-in-depth
  (MaterializeAll guards upstream; branch unreachable through public
  surface).

Disposition + verdicts in reports/scrum/_evidence/2026-05-02/.

Pattern matches feedback_cross_lineage_review.md: only Opus emits
BLOCK-class findings worth verifying; Kimi/Qwen single-reviewer
BLOCKs failed trace verification.

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

internal/materializer/materializer.go

@@ -446,9 +446,11 @@ func isoDatePartition(iso string) string {
 		t, err = time.Parse(time.RFC3339, iso)
 	}
 	if err != nil {
-		// Fallback: TS would have produced "NaN/NaN/NaN" — we use
-		// "0000/00/00" which is at least a valid path. Materializer
-		// fails its own RecordedAt validation before reaching here.
+		// Defense-in-depth only — MaterializeAll calls validISOTimestamp
+		// on RecordedAt before processSource ever invokes us, so this
+		// branch is unreachable through the public surface. Kept so a
+		// future direct caller doesn't get a panic; "0000/00/00" is at
+		// least a valid path.
 		return "0000/00/00"
 	}
 	t = t.UTC()

internal/vectord/index_test.go

@@ -561,10 +561,12 @@ func TestAdd_RecoversFromPanickingGraph(t *testing.T) {
 	// path and proceeding.
 	_ = safeGraphDelete(idx.g, "safe-test")
 }
-// playbook_record pattern: many requests in flight, each Adding a
-// unique ID to a fresh small index. Vectord's mutex serializes
-// these, but the concurrency stresses lock acquisition timing
-// against the small-index transition state.
+
+// TestAdd_SmallIndex_ConcurrentDistinctIDs reproduces the playbook_record
+// pattern: many requests in flight, each Adding a unique ID to a fresh
+// small index. Vectord's mutex serializes these, but the concurrency
+// stresses lock acquisition timing against the small-index transition
+// state.
 func TestAdd_SmallIndex_ConcurrentDistinctIDs(t *testing.T) {
 	idx, _ := NewIndex(IndexParams{Name: "concurrent_small", Dimension: 8})
 	const writers = 16