How does contact work, and is my wheelchair part of me?

Yes. The IWBF rules say the wheelchair is considered part of the player, and a personal foul is illegal contact with an opponent, which includes their wheelchair.

• Cylinder: each player has the right to the space occupied by their wheelchair and their torso in the upright seated position, including the air space above. It is measured from the palms of the hands and footrest or front bar at the front, to the back outside edge of the large wheels at the rear, and the outside edge of the large wheels at the sides.
• If a player leaves their cylinder and contact occurs with an opponent who had already established theirs, the player who left is responsible for the contact.
• A defender must not be penalised for having hands and arms extended above them within their own cylinder.
• An attacker must not cause contact with a defender in a legal guarding position by using their arms to create extra space (clear-out), or by spreading their legs or arms to cause contact during or immediately after a shot.
• A player must not hold, block, push, charge, trip or impede an opponent with a hand, arm, elbow or shoulder, or by bending into an abnormal position outside their cylinder, or play roughly or violently.

Source: IWBF Official Wheelchair Basketball Rules 2024, Art. 32 to 34.