audit_baselines: round-trip validation against live Rust data

Same shape of proof as embed_parity.sh for the embed endpoint:
take the just-shipped Go port (ca142b9) and validate it against
the actual production data the Rust legacy emits, not just unit-
test fixtures. Locks the cross-runtime parity that operators
running mixed pipelines depend on.

scripts/cutover/audit_baselines_validate.go:
- Reads /home/profit/lakehouse/data/_kb/audit_baselines.jsonl
- Parses every entry via the Go AuditBaseline struct
- Round-trips the last entry: encode → decode → field-by-field
  equality check (catches any silently-dropped JSON keys)
- Calls LoadLastBaseline against the live file (proves the public
  API works on real shapes, not just inline parsing)
- Computes BuildAuditDriftTable(first → last) — full-window
  lineage drift over the captured baselines

Live-data probe results (reports/cutover/audit_baselines_roundtrip.md):
- 7 entries parse without error
- Round-trip is byte-equal on every metric + every header field
- Drift table fires the expected verdicts:
  - p2_evidence_rows 12→82 (+583%) → warn (above 20% threshold)
  - p3_accepted/partial/rejected/human 0→non-zero → warn (the
    zero-baseline edge case TestBuildAuditDriftTable_ZeroBaseline
    was designed to lock — verified now firing on real history)
  - p4_* metrics +0% → ok (stable across the window)

What this does NOT prove (documented in the report): the Go-side
audit-FULL pipeline that PRODUCES baselines doesn't exist yet.
Only the load/append/drift substrate is ported. Operators running
audit-full from Go would still need a metric-collection pass —
that's a separate port deliberately not in this wave.

reports/cutover/SUMMARY.md gains a new row alongside the embed
parity entries; cutover-prep verification log keeps the
discipline of "verified against real data, not just fixtures."

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

reports/cutover/SUMMARY.md

@@ -7,6 +7,7 @@ what's safe to flip. Append a row when a new endpoint clears parity.
 |---|---|---|---|---|---|
 | `embed` (forced v1)     | 2026-04-30 | `/ai/embed`              | `/v1/embed`              | ✅ PASS 5/5 cos=1.000 | bit-identical with `model=nomic-embed-text` forced both sides |
 | `embed` (forced v2-moe) | 2026-04-30 | `/ai/embed`              | `/v1/embed`              | ✅ PASS 5/5 cos=1.000 | bit-identical with `model=nomic-embed-text-v2-moe` forced both sides — both Ollamas have the model |
+| `audit_baselines.jsonl` | 2026-05-01 | `data/_kb/audit_baselines.jsonl` | `internal/distillation` `LoadLastBaseline` / `AppendBaseline` / `BuildAuditDriftTable` | ✅ PASS round-trip | Live Rust file (7 entries) parses + round-trips byte-equal; lineage drift table fires correctly on zero-baseline metrics. See `audit_baselines_roundtrip.md`. |
 
 ## Wire-format drift catalog