fix: reduce file tool log noise

- treat git diff --cached --quiet rc=1 as an expected checkpoint state
  instead of logging it as an error
- downgrade expected write PermissionError/EROFS/EACCES failures out of
  error logging while keeping unexpected exceptions at error level
- add regression tests for both logging behaviors

tests/tools/test_file_tools.py

@@ -5,6 +5,7 @@ handling without requiring a running terminal environment.
 """
 
 import json
+import logging
 from unittest.mock import MagicMock, patch
 
 from tools.file_tools import (
@@ -87,13 +88,26 @@ class TestWriteFileHandler:
         mock_ops.write_file.assert_called_once_with("/tmp/out.txt", "hello world!\n")
 
     @patch("tools.file_tools._get_file_ops")
-    def test_exception_returns_error_json(self, mock_get):
+    def test_permission_error_returns_error_json_without_error_log(self, mock_get, caplog):
         mock_get.side_effect = PermissionError("read-only filesystem")
 
         from tools.file_tools import write_file_tool
-        result = json.loads(write_file_tool("/tmp/out.txt", "data"))
+        with caplog.at_level(logging.DEBUG, logger="tools.file_tools"):
+            result = json.loads(write_file_tool("/tmp/out.txt", "data"))
         assert "error" in result
         assert "read-only" in result["error"]
+        assert any("write_file expected denial" in r.getMessage() for r in caplog.records)
+        assert not any(r.levelno >= logging.ERROR for r in caplog.records)
+
+    @patch("tools.file_tools._get_file_ops")
+    def test_unexpected_exception_still_logs_error(self, mock_get, caplog):
+        mock_get.side_effect = RuntimeError("boom")
+
+        from tools.file_tools import write_file_tool
+        with caplog.at_level(logging.ERROR, logger="tools.file_tools"):
+            result = json.loads(write_file_tool("/tmp/out.txt", "data"))
+        assert result["error"] == "boom"
+        assert any("write_file error" in r.getMessage() for r in caplog.records)
 
 
 class TestPatchHandler: