fix: classify landed file mutations with diagnostics

agent/tool_result_classification.py

@@ -0,0 +1,26 @@
+"""Shared helpers for classifying tool result payloads."""
+
+from __future__ import annotations
+
+import json
+from typing import Any
+
+
+FILE_MUTATING_TOOL_NAMES = frozenset({"write_file", "patch"})
+
+
+def file_mutation_result_landed(tool_name: str, result: Any) -> bool:
+    """Return True when a file mutation result proves the write landed."""
+    if tool_name not in FILE_MUTATING_TOOL_NAMES or not isinstance(result, str):
+        return False
+    try:
+        data = json.loads(result.strip())
+    except Exception:
+        return False
+    if not isinstance(data, dict) or data.get("error"):
+        return False
+    if tool_name == "write_file":
+        return "bytes_written" in data
+    if tool_name == "patch":
+        return data.get("success") is True
+    return False