Axis limits: is the inline editor the right mechanism?

The question

Clicking the Y axis opens a small text box floating over the plot at the click point. It works, and it feels like a workaround. Is there a native mechanism that does this properly?

What it is today

• A TextBox named AxisBoundEditor, hidden, sitting in a Panel over the plot and positioned by setting its margin to the click coordinates (Chart/TrendChartView.axaml:30-34, Chart/TrendChartView.axaml.cs:207-216).
• The click is resolved against the axis region before anything else and handed to the router (Chart/TrendChartView.axaml.cs:158-160, Chart/ChartPressRouter.cs:14-24). Upper half of the axis edits the maximum, lower half the minimum (Chart/ChartAxisRegion.cs:74-77), and a double click autoscales instead.
• Enter commits, parsing with the current culture, swapping inverted bounds (Chart/ChartAxisEdit.cs:5-14) and switching the pen to manual. Escape or losing focus dismisses it.
• Only the active pen's axis is clickable (Chart/TrendChartViewModel.cs:107-110).

The pieces are separated properly: the hit test, the seed and the swap are pure and unit-tested. The awkward part is the presentation, a manually positioned control over the canvas, plus a double binding with no validation, so a non-numeric entry fails silently.

What to look at

• Avalonia's Popup or Flyout anchored to the pointer, which is the native answer to a floating editor and handles placement, light dismiss and focus without arithmetic on margins.
• NumericUpDown instead of a bare TextBox, which brings parsing, a format and range clamping.
• Whether the editor belongs on the axis at all, once the toolbar gains a proper scale group (#82) and every pen carries a stored range (#65). Three ways to set the same two numbers is two too many, and docs/architecture/trend-interaction.md:73-74 says the duplication with the toolbar is deliberate.

An answer, not a rewrite. If a popup is the mechanism, the change is small and the pure parts stay as they are.