Blender assembly pitfalls

This is a failure-mode skill, not a tool catalog. Every number below was measured on Blender 4.5.13 LTS (daeeeca98fb0) in a headless blender --background --factory-startup session. If a claim here cannot be reproduced, the claim is wrong - fix the skill, do not work around the symptom.

Read it when you are about to create, size, orient, or join geometry. Skip it for read-only scene inspection.

The failure this skill prevents always has the same shape: the code runs, no exception is raised, the viewport looks plausible, and the model is wrong. Nothing in Blender warns you. So the defence is not "be careful" - it is the Phase 1 connection map and the Phase 3 checklist at the end.

Pitfall 1 - size is a full edge, radius is a half edge, and scale= halves your intent