How to get CharacterBody3D to "snap" onto the floor?

Question

I am fairly new to coding in game engines, but have some mild programming experience outside of them.
I'm making a 2D game with 3D characters, so I am using the 3D environment minus the Z axis. For the life of me, I cannot figure out how to get the character to interact with the floor (especially slopes) in the way that I want it to. Code is being written in C#

My desired effect is as follows: The character should follow the contour of my 2D floor, as if they were riding a roller coaster across the curve. The character should not leave the floor until a jump command is explicitly entered, no matter the angle or speed of approach.

(my beautiful MSPaint artwork)
example:

Currently, I am using the MoveAndSlide() function with ApplyFloorSnap(). When I enter the jump command, I set the FloorSnapLength to 0, otherwise, I have it set to 0.25. The game will have very high movement speed, which is why I have the FloorSnapLength set so high. This causes artifacts in movement. Examples include snapping to the ground at a visible distance, odd falling into slopes, and snapping to the floor while jumping. This happens while still allowing unwanted behavior, for example entering then quickly exiting a slope will pop the character into the air. A video example is below, in a google drive link. Setting the FloorSnapLength any lower causes far more air popping off of slopes. I attempted to use the MoveAndCollide() function, but there is next to no documentation on how to use it effectively, and having any sort of gravity causes the player to get "stuck" to the floor, my guess is as a result of the constant collision return setting velocity to 0. In order to remedy this, I tried two methods. First, I tried removing gravity while on the ground. This did not give the desired effect on slopes, as going down a slope would cause the player to detach from the ground. Second, (with gravity on all the time) I tried brute-forcing movement by updating the players position directly when MoveAndCollide() returned a collision with the floor. I did this using GlobalPosition = new Vector3D(), and inserting the velocity on each axis * delta. This worked better, but is bad practice and updated the Y component of position far less often than it should have, for whatever reason.

examples:
Video example

If possible, I would vastly prefer to use MoveAndCollide(), as it gives me far more precise control over how the player moves, which is incredibly important in the game that I am creating. I have looked at the code for MoveAndSlide() in the GitHub repository in an attempt to emulate its basic ground movement, but I can't make much out of it.

Chalcopyrite

Answer 1

I found an OK solution, but it still has flaws. More experienced programmers are still wanted.

By checking if the player WAS on the ground in the last frame, IS on the ground in this frame, and if the jump command was inputted this frame, I can very reliably detect whether or not the player should be on the ground. If this check fails, and the player is off the ground when they should not be, I send a raycast down from the player to detect if there is a floor beneath them. If there is, I set their velocity for this frame to force them back into the ground. The reason for this raycast check is that my game will often have the character fall off of platforms, and I do not want them being forced into the ground at the speed of light.
This method seems to work fairly well; the only issue I have is that, at high speeds, the character can still be seen blipping into the air for a frame. Character movement still looks jagged as well, especially when moving up/down variable slopes.

Chalcopyrite