[Detail Bug] KNX GUI: Invalid numeric input resets integer parameters to minimum and persists the corrupted value

Detail Bug Report

https://app.detail.dev/org_62aa40f5-2c23-4914-a665-3bb2068af20e/bugs/bug_f50b3aae-f1a1-4189-a60c-6fc5d301e5fb

Introduced in 09f490434fc1712370be798abbd5984272ff19cd by @kewde on Jun 6, 2026

Summary

• Context: _render_int_param in apps/knx-gui/src/knx_gui/widgets/parameter_widgets.py renders every integer parameter (both NumberWidget and NumberSliderWidget) as one-line text fields and clamps the typed value when editing finishes.
• Bug: When the field's text can't be parsed as a plain integer, the except ValueError branch silently overwrites the parameter's bound value with min_value instead of preserving the prior value — destroying the previously-valid value and writing it back through on_change.
• Actual vs. expected: A single non-integer character that imgui.InputTextFlags_.chars_decimal admits (., but also +, - mid-string, *, /) — e.g. typing 5.5 into a 50 valued parameter — silently resets the stored parameter to min_value (often 0) on blur; the expected behavior is to reject the unparseable input and keep the prior value.
• Impact: Corruption of a saved project's parameter state. The wrong value is persisted through ProjectService.set_parameter → EventStore.append(SetParameter(...)) to a SQLite event history that survives app reopen (per EventStore's contract: "the history is fully re-playable and survives reopen") and is re-applied live (SetParameter.apply sets param.value on the Parameter ORM row).

Code with Bug

def _render_int_param(
    widget_id: str,
    value: str,
    min_value: int | None,
    max_value: int | None,
    on_change: Callable[[str], None],
) -> None:
    _, new_text = imgui.input_text(
        f"##{widget_id}", value, imgui.InputTextFlags_.chars_decimal
    )
    if imgui.is_item_deactivated_after_edit():
        try:
            clamped = int(new_text)
        except ValueError:
            clamped = min_value if min_value is not None else 0  # <-- BUG 🔴 overwrites prior valid value with min_value on unparseable input
        if min_value is not None:
            clamped = max(min_value, clamped)
        if max_value is not None:
            clamped = min(max_value, clamped)
        if str(clamped) != value:
            on_change(str(clamped))

Explanation

• imgui.InputTextFlags_.chars_decimal allows 0123456789.+-*/, so users can type strings like 5.5, 1+2, 3/4, etc.
• _render_int_param parses the buffer with int(new_text), which rejects those inputs and raises ValueError.
• The except ValueError handler replaces the value with min_value (commonly 0) and then calls on_change, so the UI change becomes a real model update.
• That update is persisted via the Configure panel callback chain (ProjectPlugin._handle_param_change → ProjectService.set_parameter → EventStore.append(SetParameter(...))), and replayed on reopen (SetParameter.apply assigns param.value = self.value).

Codebase Inconsistency

• The fallback to min_value was originally used when parsing a loaded default value feeding imgui.drag_int (which cannot produce non-integers). After commit 09f4904, the control switched to free-text input (input_text + chars_decimal) but kept the same fallback, changing its meaning from recover from malformed loaded defaults to silently overwrite user-entered invalid text with minimum.

Recommended Fix

On ValueError, do not substitute min_value; reject the unparseable input and keep the prior bound value:

    if imgui.is_item_deactivated_after_edit():
        try:
            clamped = int(new_text)
        except ValueError:
            return  # <-- FIX 🟢 reject unparseable input, keep prior bound value
        if min_value is not None:
            clamped = max(min_value, clamped)
        if max_value is not None:
            clamped = min(max_value, clamped)
        if str(clamped) != value:
            on_change(str(clamped))

History

This bug was introduced in commit 09f4904. That refactor extracted integer/time parameter rendering into _render_int_param and switched from imgui.drag_int to imgui.input_text with InputTextFlags_.chars_decimal, while keeping the old ValueError → min_value fallback. In the new free-text path, this fallback triggers on user-typed buffers that int() rejects, silently overwriting the prior value with the minimum.

Start in apps/knx-gui/src/knx_gui/widgets/parameter_widgets.py at _render_int_param and trace its callers for NumberWidget and NumberSliderWidget. Verify that unparseable input is rejected without changing the prior bound value or triggering on_change, while valid integers still receive the existing min/max clamping.