Structural queries over Python source: where a name is called, read, bound or asserted. It is the tool the structural-query hook and the struct-tools skill route textual questions to.

This is a cleanroom rebuild of substrate's scratch/pycodemod.py and its siblings (inbox/2026-09-25-substrate-pycodemod-port-letter.md), done module by module against a differential with the origin. Its organising rule: every query distinguishes found none from could not look. The origin returned a confident zero in at least four shapes: an f-string's text, an unreadable file, a missing libcst, and a dotted --calls target.

The tree a query reads is always an operand. There is no module-level root.