I am developing a high-end, flexible lip rigging system in Houdini 21 using APEX. I want to move away from static bone chains and create a fully procedural, curve-based solution.

The Goal (as shown in my Blender screenshots):
I have a cylinder with procedurally split edges at the mouth area. I want to implement a system that handles the following natively in APEX:

Curve-to-Joint Binding: A system where a curve (or multiple curves for upper/lower lips) drives a set of joints. These joints should be constrained to the curve points.

Dynamic Procedural Welding: Similar to the Blender Weld modifier, I need real-time vertex welding within the APEX graph. When the upper and lower lip joints approach each other, the mesh should seamlessly seal.

Advanced Lip Roll: Each joint along the lip curve needs a Roll (rotation) attribute to simulate the lip rolling in/out, which should be easily controllable via the curve’s tangents or custom attributes.

Procedural Density (Variable Controller Count): I want to be able to change the number of controllers (and joints) on the fly. For example, switching from 5 main controllers to 11 for finer detail without breaking the skinning or the APEX graph logic.

Sticky Lips / Seal: Logic that allows the lips to "stick" together within a certain distance threshold before they finally snap open.

My Questions for APEX Experts:

What is the best way to implement a Curve Constraint within an APEX Edit Graph to drive joint positions?

How should I handle the Lip Roll logic procedurally? Should I use an Orientation Along Curve approach within APEX?

Is it possible to make the Joint Count a procedural parameter that updates the APEX Rig Graph dynamically?

How can I implement a Distance-based Weld/Fuse node directly in the APEX evaluation to ensure the mouth seals perfectly when closed?

I'm looking for the most robust, "production-ready" way to set this up in H21. Any graph examples or node suggestions would be invaluable!

Wouldn't claim to be an expert in any way shape or form, but, off the top of my head:

• The component or rig::ControlSpline / rig::SampleSplineTransforms nodes should be able to get you a lot of the way there in terms of driving your joints with a curve.
  
• Procedural density should be doable (in the graph construction not the animate state). You're still going to have to do the weights though.
  
• For closing the mouth sop::fuse should work pretty well for basic things. Just put it after the bone deformation and set it to pick up a group on the geometry to fuse. You might want some fancier logic to blend it in, but should give you a start.