Add exact production-trace real replay client

runs/frontier-fidelity-envelope-v1/test_fidelity_envelope.py

@@ -214,6 +214,24 @@ class FidelityEnvelopeTest(unittest.TestCase):
             )
             self.assertEqual(steady["anchors"][0]["requests"], 20)
 
+    def test_exact_real_client_uses_the_prepared_row_vector_contract(self) -> None:
+        client = load("qwen30_exact_trace_client.py")
+        prepare = load("prepare_exact_trace.py")
+        rows = [
+            {
+                "source_index": 7,
+                "arrived_at": 1.25,
+                "input_length": 32,
+                "output_length": 4,
+                "session_id": 3,
+                "runtime_block_ids": [11, 12],
+            }
+        ]
+        digest = client.hashlib.sha256()
+        prepare.update_digest(digest, [7, 1.25, 32, 4, 3, [11, 12]])
+        self.assertEqual(client.row_vector_sha256(rows), digest.hexdigest())
+        self.assertEqual(client.ttft_slo_ms(512), 1064.0)
+
 
 if __name__ == "__main__":
     unittest.main()