feat(#62): IMP-46 cache fingerprint forwarding u1~u4 (router kwarg + step12 forward + 8 scenarios)

src/phase_z2_ai_fallback/router.py

@@ -50,6 +50,7 @@ def route_ai_fallback(
     internal_region: dict[str, Any],
     mdx_text: str,
     client: AiFallbackClient | None = None,
+    fingerprints: dict | None = None,
 ) -> AiFallbackProposal | None:
     """Route a fallback request through cache → prompt → client → validate.
 
@@ -57,13 +58,18 @@ def route_ai_fallback(
     not ``ai_adaptation_required`` — both gates short-circuit BEFORE any
     prompt/client work, so the normal-path AI call count stays at 0
     (PZ-1).
+
+    ``fingerprints`` is forwarded into ``read_proposal`` so that
+    contract / partial / catalog SHA mismatches invalidate stale cache
+    entries (IMP-46 #62 Axis R). When ``None`` the cache layer skips
+    fingerprint comparison (legacy behaviour).
     """
     if not settings.ai_fallback_enabled:
         return None
     route = v4_result.get("route") or v4_result.get("imp05_route_hint")
     if route != V4_ROUTE_AI_ADAPTATION:
         return None
-    cached = read_proposal(cache_key)
+    cached = read_proposal(cache_key, fingerprints=fingerprints)
     if cached is not None:
         validate_proposal(
             cached,

src/phase_z2_ai_fallback/step12.py

@@ -200,6 +200,7 @@ def gather_step12_ai_repair_proposals(
                 figma_partial_json=figma_partial_json,
                 internal_region=internal_region,
                 mdx_text=mdx_text,
+                fingerprints=fingerprints,
             )
         except Exception as exc:  # noqa: BLE001 — record + continue, no AI re-raise
             record["ai_called"] = True