The B5 cursor icon was re-derived in reshape, but accepted PanelFrame
messages changed the document boundary without reaching reshape. A
stationary pointer therefore kept Text over a new panel, or RowResize
after the panel disappeared.
Route panel inset changes through one helper that synchronizes dimensions
and reshapes. Keep content-only panel frames on the repaint path, so normal
panel output does not rebuild the document. Geometry epoch advancement uses
the same helper because it disowns the retained frame after resize/font
handling has already reshaped against the old presentation.
Add production-path witnesses for Present/Absent, an independent epoch
invalidation row, and a discriminator keeping content-only frames off the
reshape path. All four documented mutations fire.