Make pod addressability work even in meshes and drop fallbacks

[markusthoemmes]

See exhaustive proposal here: https://docs.google.com/document/d/1vUDC_-qWei81QcjI8ZjZJ0Tc4SswUA1gBTSvBqy6CBY/edit?resourcekey=0-C_Yh8KqcLA6Mcr3CQs5Q1Q.

I'll use this as an umbrella to link PRs to.

[evankanderson]

/triage accepted