Add IAuditLog interface for tamper-proof trade audit trail

Author: e

include/flox/audit/audit_log.h

@@ -0,0 +1,57 @@
+/*
+ * Flox Engine
+ * Developed by FLOX Foundation (https://github.com/FLOX-Foundation)
+ *
+ * Copyright (c) 2025 FLOX Foundation
+ * Licensed under the MIT License. See LICENSE file in the project root for full
+ * license information.
+ */
+
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace flox
+{
+
+struct AuditEntry
+{
+  int64_t seq = 0;
+  std::string ts;
+  std::string actor;
+  std::string action;
+  int64_t trade_id = 0;
+  std::string details;
+  std::string source;
+  std::string prev_hash;
+  std::string hash;
+};
+
+struct AuditVerifyResult
+{
+  int64_t total = 0;
+  int64_t verified = 0;
+  bool intact = false;
+  int64_t broken_at_seq = 0;
+  std::string error;
+};
+
+struct IAuditLog
+{
+  virtual ~IAuditLog() = default;
+
+  virtual void audit(std::string_view actor, std::string_view action,
+                     int64_t tradeId, std::string_view details,
+                     std::string_view source = "") = 0;
+
+  virtual std::vector<AuditEntry> getLog(int limit = 100, int64_t beforeSeq = 0,
+                                         std::string_view actor = "",
+                                         int64_t tradeId = 0) = 0;
+
+  virtual AuditVerifyResult verify() = 0;
+};
+
+}  // namespace flox