fix corporate action ledger replay invariants

app/domain/corporate_actions.py

@@ -2,6 +2,14 @@
 from __future__ import annotations
 from dataclasses import dataclass
 from decimal import Decimal, ROUND_HALF_UP
+import hashlib
+import json
+
+def canonical_payload_hash(payload: object) -> str:
+    if hasattr(payload, "model_dump"):
+        payload = payload.model_dump(mode="json", exclude_none=True)
+    encoded = json.dumps(payload, sort_keys=True, separators=(",", ":"), ensure_ascii=False).encode()
+    return hashlib.sha256(encoded).hexdigest()
 
 class CorporateActionError(ValueError):
     code = "INVALID_CORPORATE_ACTION_RATIO"