fix(file_tools): refresh staleness timestamp after writes (#4390)

After a successful write_file or patch, update the stored read
timestamp to match the file's new modification time.  Without this,
consecutive edits by the same task (read → write → write) would
false-warn on the second write because the stored timestamp still
reflected the original read, not the first write.

Also renames the internal tracker key from 'file_mtimes' to
'read_timestamps' for clarity.

tests/tools/test_file_staleness.py

@@ -221,7 +221,7 @@ class TestCheckFileStalenessHelper(unittest.TestCase):
             _read_tracker["t1"] = {
                 "last_key": None, "consecutive": 0,
                 "read_history": set(), "dedup": {},
-                "file_mtimes": {"/tmp/other.py": 12345.0},
+                "read_timestamps": {"/tmp/other.py": 12345.0},
             }
         self.assertIsNone(_check_file_staleness("/tmp/x.py", "t1"))
 
@@ -231,7 +231,7 @@ class TestCheckFileStalenessHelper(unittest.TestCase):
             _read_tracker["t1"] = {
                 "last_key": None, "consecutive": 0,
                 "read_history": set(), "dedup": {},
-                "file_mtimes": {"/nonexistent/path": 99999.0},
+                "read_timestamps": {"/nonexistent/path": 99999.0},
             }
         # File doesn't exist → stat fails → returns None (let write handle it)
         self.assertIsNone(_check_file_staleness("/nonexistent/path", "t1"))

tools/file_tools.py

@@ -136,9 +136,12 @@ _file_ops_cache: dict = {}
 #                   Used to skip re-reads of unchanged files.  Reset on
 #                   context compression (the original content is summarised
 #                   away so the model needs the full content again).
-#   "file_mtimes":  dict mapping resolved_path → mtime float at last read.
-#                   Used by write_file and patch to detect when a file was
-#                   modified externally between the agent's read and write.
+#   "read_timestamps": dict mapping resolved_path → modification-time float
+#                      recorded when the file was last read (or written) by
+#                      this task.  Used by write_file and patch to detect
+#                      external changes between the agent's read and write.
+#                      Updated after successful writes so consecutive edits
+#                      by the same task don't trigger false warnings.
 _read_tracker_lock = threading.Lock()
 _read_tracker: dict = {}
 
@@ -401,7 +404,7 @@ def read_file_tool(path: str, offset: int = 1, limit: int = 500, task_id: str =
             try:
                 _mtime_now = os.path.getmtime(resolved_str)
                 task_data["dedup"][dedup_key] = _mtime_now
-                task_data.setdefault("file_mtimes", {})[resolved_str] = _mtime_now
+                task_data.setdefault("read_timestamps", {})[resolved_str] = _mtime_now
             except OSError:
                 pass  # Can't stat — skip tracking for this entry
 
@@ -500,6 +503,24 @@ def notify_other_tool_call(task_id: str = "default"):
             task_data["consecutive"] = 0
 
 
+def _update_read_timestamp(filepath: str, task_id: str) -> None:
+    """Record the file's current modification time after a successful write.
+
+    Called after write_file and patch so that consecutive edits by the
+    same task don't trigger false staleness warnings — each write
+    refreshes the stored timestamp to match the file's new state.
+    """
+    try:
+        resolved = str(Path(filepath).expanduser().resolve())
+        current_mtime = os.path.getmtime(resolved)
+    except (OSError, ValueError):
+        return
+    with _read_tracker_lock:
+        task_data = _read_tracker.get(task_id)
+        if task_data is not None:
+            task_data.setdefault("read_timestamps", {})[resolved] = current_mtime
+
+
 def _check_file_staleness(filepath: str, task_id: str) -> str | None:
     """Check whether a file was modified since the agent last read it.
 
@@ -515,7 +536,7 @@ def _check_file_staleness(filepath: str, task_id: str) -> str | None:
         task_data = _read_tracker.get(task_id)
         if not task_data:
             return None
-        read_mtime = task_data.get("file_mtimes", {}).get(resolved)
+        read_mtime = task_data.get("read_timestamps", {}).get(resolved)
     if read_mtime is None:
         return None  # File was never read — nothing to compare against
     try:
@@ -543,6 +564,9 @@ def write_file_tool(path: str, content: str, task_id: str = "default") -> str:
         result_dict = result.to_dict()
         if stale_warning:
             result_dict["_warning"] = stale_warning
+        # Refresh the stored timestamp so consecutive writes by this
+        # task don't trigger false staleness warnings.
+        _update_read_timestamp(path, task_id)
         return json.dumps(result_dict, ensure_ascii=False)
     except Exception as e:
         if _is_expected_write_exception(e):
@@ -594,6 +618,11 @@ def patch_tool(mode: str = "replace", path: str = None, old_string: str = None,
         result_dict = result.to_dict()
         if stale_warnings:
             result_dict["_warning"] = stale_warnings[0] if len(stale_warnings) == 1 else " | ".join(stale_warnings)
+        # Refresh stored timestamps for all successfully-patched paths so
+        # consecutive edits by this task don't trigger false warnings.
+        if not result_dict.get("error"):
+            for _p in _paths_to_check:
+                _update_read_timestamp(_p, task_id)
         result_json = json.dumps(result_dict, ensure_ascii=False)
         # Hint when old_string not found — saves iterations where the agent
         # retries with stale content instead of re-reading the file.