The old 2x2 grid for 3+ members produced a cramped, misaligned look
(circles cut off inside their own border, no overlap, just four small
disks in a grid). The 2-member overlap aesthetic — equal-size tiles
that overlap diagonally — was the visual gold standard but only
existed for that one count.
Extend the same "huddle of overlapping faces" aesthetic to all
member counts:
• 3 members → equilateral triangle of 62%-size tiles (top, bl, br)
• 4 members → diamond of 58%-size tiles (top, right, bottom, left)
• 5-10 members → diamond with `+N` overflow occupying the bottom
slot (z-index boosted above neighbors so the digit is never clipped)
Tiles are positioned radially around the box center on a circle of
radius (S − T) / 2 so the farthest edges of each tile graze the
bounding rect — no clipping, no wasted whitespace. Z-index descends
clockwise from the top slot so each tile tucks slightly under its
clockwise neighbor, mirroring the 2-member z-stack.
The 0/1/2-member cases and the icon-override branch are unchanged.
Props interface unchanged — no call-site updates needed.
Tests updated to assert the new layout markers (`triangle`, `diamond`)
and to verify the geometry (top tile in triangle has smallest `top`;
overflow tile in diamond has largest `top`). 11/11 AvatarStack tests
pass; 360/360 web tests pass; typecheck clean.
design-system.md spec updated with the new layout table + geometry
section.