fix(export): prevent silent truncation of parameter values smaller than 1e-6

The `.6f` format specifier in `_format_params()` silently truncates any
value below 1e-6 to "0", causing data loss on save→load round-trips.

Changed to `.10f` which preserves all IEEE 754 single-precision float
significant digits while remaining in decimal notation.

Fixes #1400

Signed-off-by: Yash Goel <yashgoel249@gmail.com>

Author: yashhzd

ardupilot_methodic_configurator/data_model_par_dict.py

@@ -255,19 +255,19 @@ def _format_params(self, file_format: str = "missionplanner") -> list[str]:
             sorted_dict = ParDict(sorted_items)
             formatted_params = [
                 (
-                    f"{key},{format(parameter.value, '.6f').rstrip('0').rstrip('.')}  # {parameter.comment}"
+                    f"{key},{format(parameter.value, '.10f').rstrip('0').rstrip('.')}  # {parameter.comment}"
                     if isinstance(parameter, Par) and parameter.comment
-                    else f"{key},{format(parameter.value if isinstance(parameter, Par) else parameter, '.6f').rstrip('0').rstrip('.')}"  # noqa: E501 # pylint: disable=line-too-long
+                    else f"{key},{format(parameter.value if isinstance(parameter, Par) else parameter, '.10f').rstrip('0').rstrip('.')}"  # noqa: E501 # pylint: disable=line-too-long
                 )
                 for key, parameter in sorted_dict.items()
             ]
         elif file_format == "mavproxy":
             sorted_dict = ParDict(dict(sorted(self.items())))
             formatted_params = [
                 (
-                    f"{key:<16} {parameter.value:<8.6f}  # {parameter.comment}"
+                    f"{key:<16} {parameter.value:<8.10f}  # {parameter.comment}"
                     if isinstance(parameter, Par) and parameter.comment
-                    else f"{key:<16} {parameter.value if isinstance(parameter, Par) else parameter:<8.6f}"
+                    else f"{key:<16} {parameter.value if isinstance(parameter, Par) else parameter:<8.10f}"
                 )
                 for key, parameter in sorted_dict.items()
             ]

tests/test_data_model_par_dict.py

@@ -563,8 +563,8 @@ def test_user_can_export_parameters_to_mavproxy_format(self, parameter_dict) ->
                 content = f.read()
 
             # MAVProxy format uses fixed-width columns
-            assert "ACRO_YAW_P       4.500000  # Yaw P gain" in content
-            assert "GPS_TYPE         1.000000" in content
+            assert "ACRO_YAW_P       4.5000000000  # Yaw P gain" in content
+            assert "GPS_TYPE         1.0000000000" in content
         finally:
             os.unlink(output_file)
 
@@ -943,7 +943,7 @@ def test_user_can_format_parameters_for_mavproxy(self, parameter_dict) -> None:
 
         # Assert: Correct MAVProxy format (space-separated, fixed width)
         yaw_line = next((line for line in formatted if "ACRO_YAW_P" in line), "")
-        assert yaw_line == "ACRO_YAW_P       4.500000  # Yaw P gain"
+        assert yaw_line == "ACRO_YAW_P       4.5000000000  # Yaw P gain"
 
     def test_user_receives_error_for_unsupported_format(self, parameter_dict) -> None:
         """
@@ -959,6 +959,36 @@ def test_user_receives_error_for_unsupported_format(self, parameter_dict) -> Non
         with pytest.raises(SystemExit, match="Unsupported file format"):
             parameter_dict._format_params("invalid_format")  # pylint: disable=protected-access
 
+    def test_user_preserves_small_parameter_values_on_export(self) -> None:
+        """
+        User preserves parameter values smaller than 1e-6 during export.
+
+        GIVEN: A user has parameters with very small but nonzero values
+        WHEN: They export and reimport using MissionPlanner or MAVProxy format
+        THEN: The values should survive the round-trip without silent data loss
+        """
+        # Arrange: Parameters with values that would be truncated by .6f formatting
+        small_value_params = ParDict(
+            {
+                "TINY_VAL": Par(0.0000001, "Very small value"),
+                "MICRO_VAL": Par(0.0000005, "Another small value"),
+                "BOUNDARY_VAL": Par(0.000001, "Boundary value"),
+                "NORMAL_VAL": Par(1.5, "Normal value"),
+            }
+        )
+
+        for file_format in ("missionplanner", "mavproxy"):
+            formatted = small_value_params._format_params(file_format)  # pylint: disable=protected-access
+
+            # Extract the numeric value strings from the formatted output
+            for line in formatted:
+                if "TINY_VAL" in line:
+                    assert "0.0000001" in line, f"Value 1e-7 lost in {file_format} format: {line}"
+                if "MICRO_VAL" in line:
+                    assert "0.0000005" in line, f"Value 5e-7 lost in {file_format} format: {line}"
+                if "BOUNDARY_VAL" in line:
+                    assert "0.000001" in line, f"Value 1e-6 lost in {file_format} format: {line}"
+
     def test_user_can_annotate_parameters_with_comments(self, parameter_dict) -> None:
         """
         User can add comments to parameters using a lookup table.