primaryCapacity property
The finite, non-negative width available to the primary action region.
A window-level host can derive this from MediaQuery.sizeOf(context), but
should reserve space for adjacent toolbar content. This value is a layout
decision input, not a clipping or scrolling constraint. If hard placement
produces a wider result, the caller owns the surrounding overflow policy.
primaryCapacity: 220 [Save] [Search]
primaryCapacity: 96 [ S ] [ ? ]
pinned over capacity: [Pinned] ---> caller-owned boundary
Implementation
final double primaryCapacity;