Contraindications are redirects
Every "skip this pose" on this site is really "choose the listed variation instead." Knee pain in pigeon redirects to supine figure-4; neck issues redirect shoulder stand to legs-up-the-wall. The practice continues; the shape adapts — that is the entire skill of working with a body.
Pain is information, not a challenge
Stretching sensation is welcome; joint pain, nerve sensation (tingling, radiating), and sharp anything are exits. The rule is instant and total — and it applies doubly to backbends and inversions, where the ego is loudest and the spine is most involved.
The teacher-and-provider loop
A qualified teacher sees what you cannot feel; a healthcare provider knows what no yoga page can. New practitioners, injured practitioners, and pregnant practitioners use both — and the pose library here is the shared language for those conversations, not the replacement for them.