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 navigation-bar 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: 200 [Save] [Search]
primaryCapacity: 88 [ S ] [ ? ]
pinned over capacity: [Pinned] ---> caller-owned boundary
Implementation
final double primaryCapacity;