Architecture

The clone copies the mouse's USB identity.

Part	Role
Host chip	Reads the mouse on `USB3`. Sets the mouse's four relative axes: how much injected motion they carry, and when it is emitted.
Device chip	Presents the clone to the PC and merges the host chip's axes into each report it emits.
Link	Host chip to device chip: each report and the motion riding with it. Device chip to host chip: the PC's requests for the mouse.

   real mouse                     game PC
        |                            ^
        | USB3                       | USB1
        v                            |
  +-----------+                +-----------+
  | host chip | ---- link ---> |device chip|
  +-----------+                +-----------+
                                     ^
                                     | USB2 (CH343 serial)
                                     |
                                control PC

Three connections:

Port	Connects to
`USB3`	Real mouse.
`USB1`	PC receiving the mouse.
`USB2`	Program driving the box, over a CH343 serial link.

The program sends movement, button, and scroll commands in the binary protocol.

PC outputReal mouse plus injected input

The PC enumerates the same model of mouse, with the same buttons and capabilities. Injected input adds to native input (Injection model).

Program	Box
Sends input	Layers injected motion, scroll, and button state onto native input.
Goes quiet	Returns to passthrough per the safety rule.

Two computersSeparate control PC

The program on USB2 runs on a different computer from the PC on USB1.

Port wiring, and the one pairing to avoid, on Hardware.