Dynamically changing sheet height doesn't respect snapping constraints

[fujidaiti]

@fujidaiti What needs to be done to have a dynamically growing sheet while having set a custom minExtent? E.g. the sheet contains a Column with a Stateful widget as first element, let's say a Text box which may have either 2 or 3 lines. The second element of the column is a button.
Initially the sheet is rendered with 2 lines of text with maxExtent and initialExtent of Èxtent.proportional(1), so the button is perfectly aligned with the bottom of the screen.
After a few seconds the text box widget updates the state and has now 3 lines of text. But that leads to the situation that all content below the text box is pushed down, so the button is clipped by the bottom screen edge (absolut extent stays the same but proportional extent is now something like 0.9...)
I would rather have the sheet growing upwards, keeping the button completely visible, means the proportional extent should stay at 1 (absolute extent would increase by the height of the text line height).

tl;dr: While a custom minimum extent is set, the sheet should keep its extent when the content grows, if currentExtent == maxExtent.

Here's a minimal example of the situation:

DraggableSheet(
  controller: sheetController,
  minExtent: Extent.pixels(100.0),
  child: SheetContentScaffold(
    appBar: SomeHeaderWidget(),
    body: Padding(
      padding: EdgeInsets.symmetric(horizontal: 24),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          SizedBox(height: 12),
          SomeStatefulTextBox(),
          SizedBox(height: 12),
          SomeActionButton(),
        ],
      ),
    ),
  ),
);

Originally posted by @codeOfJannik in #203 (comment)

[codeOfJannik]

@fujidaiti Thanks for creating this bug ticket. But I think the title is kind of misleading since my issue is not related to anything with the keyboard.