distillation: fix 7 grounding bugs found by Kimi audit

Kimi For Coding (api.kimi.com, kimi-for-coding) ran a forensic audit on
distillation v1.0.0 with full file content. 7/7 flags verified real on
grep. Substrate now matches what v1.0.0 claimed: deterministic, no
schema bypasses, Rust tests compile.

Fixes:
- mode.rs:1035,1042  matrix_corpus Some/None -> vec![..]/vec![]; cargo
                     check --tests now compiles (was silently broken;
                     only bun tests were running)
- scorer.ts:30       SCORER_VERSION env override removed - identical
                     input now produces identical version stamp, not
                     env-dependent drift
- transforms.ts:181  auto_apply wall-clock fallback (new Date()) ->
                     deterministic recorded_at fallback
- replay.ts:378      recorded_run_id Date.now() -> sha256(recorded_at);
                     replay rows now reproducible given recorded_at
- receipts.ts:454,495  input_hash_match hardcoded true was misleading
                       telemetry; bumped DRIFT_REPORT_SCHEMA_VERSION 1->2,
                       field is now boolean|null with honest null when
                       not computed at this layer
- score_runs.ts:89-100,159  dedup keyed only on sig_hash made
                            scorer-version bumps invisible. Composite
                            sig_hash:scorer_version forces re-scoring
- export_sft.ts:126  (ev as any).contractor bypass emitted "<contractor>"
                     placeholder for every contract_analyses SFT row.
                     Added typed EvidenceRecord.metadata bucket;
                     transforms.ts populates metadata.contractor;
                     exporter reads typed value

Verification (all green):
  cargo check -p gateway --tests   compiles
  bun test tests/distillation/     145 pass / 0 fail
  bun acceptance                   22/22 invariants
  bun audit-full                   16/16 required checks

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

scripts/distillation/receipts.ts

@@ -451,7 +451,7 @@ export function buildDrift(current: RunSummary, prior: RunSummary | null): Drift
         delta_accepted: cur.accepted,
         delta_quarantined: cur.quarantined,
         pct_change_out: null,
-        input_hash_match: false,
+        input_hash_match: null,            // no prior stage to compare
         output_hash_match: false,
         deterministic_violation: false,
         notes: ["stage not present in prior run"],
@@ -461,12 +461,12 @@ export function buildDrift(current: RunSummary, prior: RunSummary | null): Drift
     }
     const pct = pctChange(pri.records_out, cur.records_out);
     const out_match = pri.output_hash === cur.output_hash;
-    const inp_match = (current.stages.find(s => s.stage === cur.stage)?.output_hash ?? "")
-                    !== "" /* placeholder */;
-    // We have output_hash on stage summaries but not input_hash —
-    // input_hash lives on the full StageReceipt, which we can re-read
-    // from the run dir if needed. For simplicity, drift compares the
-    // OUTPUT hashes (what really changed).
+    // input_hash is NOT materialized into stage summaries (lives on the
+    // per-stage StageReceipt files on disk). We don't load them here, so
+    // we honestly report null. Schema v2 makes this explicit; v1 returned
+    // `true` unconditionally which made deterministic_violation always
+    // false even when it should have alerted. Cross-run determinism
+    // enforcement is its own pass — see ./scripts/distill audit-full.
     const notes: string[] = [];
     if (pct !== null && Math.abs(pct) > DRIFT_THRESHOLD_PCT) {
       const dir = pct > 0 ? "spike" : "drop";
@@ -492,9 +492,9 @@ export function buildDrift(current: RunSummary, prior: RunSummary | null): Drift
       delta_accepted: cur.accepted - pri.accepted,
       delta_quarantined: cur.quarantined - pri.quarantined,
       pct_change_out: pct,
-      input_hash_match: true,           // simplified — see comment above
+      input_hash_match: null,           // not computed at this layer; see comment above
       output_hash_match: out_match,
-      deterministic_violation: false,   // requires input_hash match, see future tightening
+      deterministic_violation: false,   // requires input_hash match — null means "unknown", not "verified"
       notes,
     });
   }