Cloth push-back and pass-through

[josemendez]

Did you mean lambda = constraint * ( invMassA + invMassB)?

which is consistent with PBD paper/slides and Obi code:
BurstContact.SolveAdhesion {
...
     float dlambda = -constraint / TotalNormalInvMass;
...
}

Nope. Both the PBD paper and Obi's code divide by the total inverse mass. A / (1 / B) = A * B.

Still, constraint * (massA + massB) is not correct since 1/A + 1/B != 1/(A+B), should have said constraint / (1/massA + 1/mass B). My bad!

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Then velocity of the rigidbody is calculated here?

BurstMath.ApplyImpulse {
...
    linearDeltas[rigidbodyIndex]  += rigidbodies[rigidbodyIndex].inverseMass * impulseWS;
...
}

That's a linear velocity delta, not the final velocity. linearDelta is then added to the rigidbody's linear velocity at the start of the frame. Same with the angular velocity.

Then somehow Unity calculates something that interacts with the joint force.

Unity solves for impulses, same thing Obi does. You accumulate multiple impulses on a rigidbody (some come from Obi, some come from Unity joints), and end up with the final velocity.