Lightweight spar frame: hollow-cored bones and a narrow build, quick and hard to hit, easy to shove.
A frame built light: hollow-cored bones, a narrow, sparing build, mass pared wherever the germline could spare it. The bearer is quick, hard to land a hit on, and lighter on their feet than their strength would suggest. The same parsimony that makes them fast makes them easy to move -- a spar-framed body is light enough to knock aside, and it carries less than a baseline before the load tells.
Effect Text: +1 DEX; +1 AC; treat carried weight as one encumbrance step lighter. Carry capacity reduced 25%; -1 to saves vs. knockdown, trip, and forced movement.
Lore Note: A Confederation line shaped by the Great Ships, where every kilogram was charged against a finite life-support budget and a smaller body was a cheaper body. It bred true in the generation-ship descendants and is now common in spacer stock and Skell-adjacent lines. Helix sells the refined frame to pilots and scouts who value the speed and the small target profile, and warns nobody about the carry penalty, because the buyers already know.