A container's outer grid cell and its own inner content grid are sized by
two independent calculations that only agree when the container is
scrollable and expanded. When collapsed, or when non-scrollable content
needs more rows than declared, the inner grid keeps rendering at its old/
content-driven size while the outer cell shrinks or stays fixed, leaving
an invisible-but-space-occupying box that inflates the board's scroll
height into a visible empty gap below the container.
Pass the outer instance's collapsed row count down as a
viewportRowCountOverride so the inner grid matches it exactly when
collapsed, and grow the outer placement's height to the already-computed
content minimum (getContainerMinimumSizes) for non-scrollable containers
so it stays in sync with the inner grid's own growth.
Bergasha
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