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/export_sft.ts

@@ -122,9 +122,18 @@ function synthesizeSft(
     case "observer_reviews":
       instruction = `Observer-review the latest attempt on '${ev.source_files?.[0] ?? "<file>"}'. Verdict: accept | reject | cycle.`;
       break;
-    case "contract_analyses":
-      instruction = `Analyze contractor '${(ev as any).contractor ?? "<contractor>"}' for permit '${ev.task_id.replace(/^permit:/, "")}'. Recommend with risk markers.`;
+    case "contract_analyses": {
+      // Read contractor from the typed metadata bucket (populated in
+      // transforms.ts for contract_analyses rows). Pre-2026-04-27 this
+      // used `(ev as any).contractor` and silently emitted "<contractor>"
+      // for every row because EvidenceRecord didn't carry the field.
+      const contractor = typeof ev.metadata?.contractor === "string" ? ev.metadata.contractor : null;
+      const permit = ev.task_id.replace(/^permit:/, "");
+      instruction = contractor
+        ? `Analyze contractor '${contractor}' for permit '${permit}'. Recommend with risk markers.`
+        : `Analyze permit '${permit}'. Recommend with risk markers.`;
       break;
+    }
     case "outcomes":
       instruction = `Run scenario; report per-event outcome with citations.`;
       break;