Implemented checker as described in internal-docs/notes4coding/checker_design.md

docs/examples/modbus.json

@@ -0,0 +1,16 @@
+{
+  "functions": [
+    {
+      "function": 3,
+      "name": "read_holding_registers",
+      "request": [
+        {"name":"starting_address","type":"u16"},
+        {"name":"quantity","type":"u16"}
+      ],
+      "response": [
+        {"name":"byte_count","type":"u8"},
+        {"name":"registers","type":"bytes","length_from":"byte_count"}
+      ]
+    }
+  ]
+}

docs/examples/report.json

@@ -0,0 +1,31 @@
+{
+  "summary": {
+    "total_packets": 1,
+    "total_findings": 1,
+    "fatal": 0,
+    "error": 1,
+    "warn": 0,
+    "info": 0
+  },
+  "findings": [
+    {
+      "pcap_index": 0,
+      "event_id": 1,
+      "severity": "error",
+      "code": "expected_field_mismatch",
+      "message": "Field mismatch for quantity",
+      "flow": {
+        "src_ip": "10.0.0.10",
+        "src_port": 51012,
+        "dst_ip": "10.0.0.20",
+        "dst_port": 502
+      },
+      "observed": {
+        "field": "quantity",
+        "observed": 1,
+        "expected": 2
+      },
+      "expected": null
+    }
+  ]
+}

docs/examples/trace.meta.jsonl

@@ -0,0 +1 @@
+{"trace_id":"example-trace","event_id":1,"pcap_index":0,"ts_ns":1736451234567890000,"direction":"c2s","flow":{"src_ip":"10.0.0.10","src_port":51012,"dst_ip":"10.0.0.20","dst_port":502},"expected":{"modbus":{"transaction_id":513,"unit_id":1,"function_code":3},"fields":{"starting_address":0,"quantity":2}}}