matrix: Shape B — inject playbook misses + 6/6 paraphrase recovery

The v0 boost-only stance documented in internal/matrix/playbook.go:22-27
("the boost only re-ranks results that ALREADY surfaced from the regular
retrieval") couldn't promote recorded answers that dropped out of a
paraphrase's top-K. playbook_lift_002 surfaced exactly that gap: 0/2
paraphrase recoveries because the recorded answers weren't in regular
retrieval at all (rank=-1).

Shape B: when warm-pass retrieval doesn't surface a playbook hit's
answer, inject a synthetic Result for it directly. Distance =
playbook_hit_distance × BoostFactor — same formula as the boost path so
injections land in comparable distance space. Caller re-sorts +
truncates after both boost and inject have run.

Result on playbook_lift_003 (Shape B + paraphrase pass):

  Verbatim discovery        6
  Verbatim lift             2 / 6
  **Paraphrase top-1**      **6 / 6**
  Paraphrase any-rank in K  6 / 6
  Mean Δ top-1 distance     -0.1637 (warm closer than cold)

Every paraphrase the judge generated landed the v1-recorded answer at
top-1 of the new query's results. The learning property holds — cosine
on embed(paraphrase) finds the recorded query's vector within
DefaultPlaybookMaxDistance (0.5), and Shape B injects the answer.

Verbatim lift dropped from v1's 7/8 because Shape B cross-pollinates
recorded answers across queries. w-4435 (Q2's recording) appears as
warm top-1 for several other queries because their embeddings are
within the playbook hit threshold of "OSHA-30 forklift Wisconsin." This
is a feature, not a bug — the matrix layer's purpose is to share
knowledge across queries — but the lift metric only counts "warm top-1
== cold judge best," so cross-pollinated lifts don't register. A v3
metric would re-judge warm pass to measure true judge improvement.

Tests:
- TestInjectPlaybookMisses_AddsMissingAnswers — primary claim
- TestInjectPlaybookMisses_SkipsAnswersAlreadyPresent — no double-inject
- TestInjectPlaybookMisses_DedupesPerAnswer — multi-hit same answer
- TestInjectPlaybookMisses_EmptyHits — fast-path no-op

Driver fix: ParaphraseRecordedRank int → *int. The `omitempty` int
silently dropped rank=0 (top-1, the WANTED value) from JSON, making the
v003 report show "null" instead of "0" for every successful recovery.
Pointer keeps nil/rank-0 distinguishable.

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

scripts/playbook_lift/main.go

@@ -85,10 +85,18 @@ type queryRun struct {
 	// Paraphrase pass — only populated when --with-paraphrase. Tests
 	// the playbook's actual learning property: does a recorded entry
 	// for query Q help a similar-but-different query Q'?
+	//
+	// ParaphraseRecordedRank semantics:
+	//   nil    = paraphrase pass didn't run for this query (no playbook
+	//            was recorded in cold pass, so nothing to test)
+	//   0      = recorded answer landed at top-1
+	//   1..K-1 = recorded answer present in top-K at that rank
+	//   -1     = recorded answer absent from top-K
+	// Pointer (not int) so nil and rank-0 are distinguishable in JSON.
 	ParaphraseQuery        string `json:"paraphrase_query,omitempty"`
 	ParaphraseTop1ID       string `json:"paraphrase_top1_id,omitempty"`
-	ParaphraseRecordedRank int    `json:"paraphrase_recorded_rank,omitempty"` // -1 if not in top-K
-	ParaphraseLift         bool   `json:"paraphrase_lift,omitempty"`          // recorded answer at rank 0 for paraphrase
+	ParaphraseRecordedRank *int   `json:"paraphrase_recorded_rank,omitempty"`
+	ParaphraseLift         bool   `json:"paraphrase_lift,omitempty"` // recorded answer at rank 0 for paraphrase
 
 	Note string `json:"note,omitempty"`
 }
@@ -273,7 +281,8 @@ func main() {
 			resp, err := matrixSearch(hc, *gw, paraphrase, corpora, *k, true)
 			if err != nil || len(resp.Results) == 0 {
 				runs[i].Note = appendNote(runs[i].Note, fmt.Sprintf("paraphrase search failed: %v", err))
-				runs[i].ParaphraseRecordedRank = -1
+				missed := -1
+				runs[i].ParaphraseRecordedRank = &missed
 				continue
 			}
 			runs[i].ParaphraseTop1ID = resp.Results[0].ID
@@ -284,7 +293,7 @@ func main() {
 					break
 				}
 			}
-			runs[i].ParaphraseRecordedRank = recordedRank
+			runs[i].ParaphraseRecordedRank = &recordedRank
 			if recordedRank == 0 {
 				runs[i].ParaphraseLift = true
 				paraphraseTop1Lifts++