The two selection categories used to arbitrate ownership of the panel by
poking each other's widgets: buildFieldSelection() called clearContent()
and buildEmpty(), buildEmpty() hid the four entity widgets, and
hideAllWidgets() hid the scrap label. Splitting the halves apart without
naming an arbiter would only have spread that across a class boundary.
SelectedBuildingPanel is now the sole arbiter. It still receives all
three selection events, forwards the two field ones to the embedded
FieldSelectionPanel, and drops its own selection and content as soon as
the field panel reports a selection (yieldToFieldSelection), mirroring
what onSelectionChanged() already did in the other direction. The field
panel decides only what to render and whether it is visible at all.
Dropping the field branch of refreshSelectionDisplay() is behaviour
preserving: whenever the field category owns the panel, m_singleBuildingId
is null, so the building refresh returns immediately anyway.
clearContent() and buildEmpty() became identical once the cross-half
hiding was gone, so only buildEmpty() remains.
Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YHcUerKAZKWNvSKJxYKbnG
