Quick answer: Unity 2D Animation bone weights painted in editor but ignored at runtime? Sprite Library Resolver needs the Sprite Skin component on the same GameObject - not on a child.
Editor preview shows the sprite deforming. Runtime: it's a rigid sprite that translates with the rig but doesn't bend.
Put Sprite Skin on the renderer
The component must sit on the GameObject that has the SpriteRenderer. Detaching breaks the binding.
Verify weights in inspector
Sprite editor > Skinning Editor. Weights show as colored gradient. If empty, weights weren't saved - apply explicitly.
Use 2D Animation 9.0+
Older versions had a binding bug fixed in 9.0. Update via Package Manager.
“2D Animation has component-placement rules. The rules are not obvious.”
For a multi-character project, build a prefab template that puts every required component in the right place. Variants inherit correctness.