diff --git a/docs/tickets/ticket-000028-multi-modality-witness.md b/docs/tickets/ticket-000028-multi-modality-witness.md
index 944767d..babf238 100644
--- a/docs/tickets/ticket-000028-multi-modality-witness.md
+++ b/docs/tickets/ticket-000028-multi-modality-witness.md
@@ -261,10 +261,18 @@ if canonical_match is not None:
     witness = None
     if policy.get("canonical_witness_enabled", False):
         from arborist.qa.witness import run_witness
-        # Cache lookup is a no-op closure pre-#000027 (always returns
-        # None). Post-#000027 it's the actual canonical_cache lookup.
-        def _cache_lookup() -> bytes | None:
-            return None  # TODO: wire post-#000027
+        # Cache lookup closes over the prior persisted row's answer
+        # bytes (post-#000027 / e19aed8). The real implementation in
+        # arborist/qa/query.py:2158-2172 reads the cached_row picked
+        # up at the top of the canonical branch — comparing against
+        # that prior row, not anything we'd write in the same call,
+        # so the leg is non-tautological.
+        _cached_bytes = (
+            cached_row["answer_text"].encode("utf-8", errors="surrogatepass")
+            if cached_row is not None
+            else None
+        )
+        _cache_lookup = lambda: _cached_bytes  # noqa: E731
         witness = run_witness(
             question=question,
             pi_star_ref=pi_star_ref,