[MrDavidAlv]

The tool's continuous-rotation SG90 turns a pulse into a speed, not an angle, so it is not a joint. The driver now takes it as a gpio with a speed interface from -1 to 1: stop_us is the pulse at which it stands still, us_per_speed the pulse added for full speed, both declared in the calibration like the rest. A speed of zero sends no pulse at all, because the stopping pulse is a trim that drifts and no pulse always stops the servo; the channel is off when the driver activates, and anything past full speed is held to it.

The description gives the real arm the tool once the calibration names its stop pulse, on a channel of its own. config/hardware.yaml adds tool_controller, a forward_command_controller on that interface, which only the real arm has, and keeps the tool out of /joint_states, where robot_state_publisher and MoveIt read the arm's joints. arm.launch.py spawns it.

Tests: the driver keeps the tool off until it is asked to turn, sends the right pulse for half speed, never passes full speed, switches off again at zero, and refuses a tool on a joint's channel; the description carries the tool's calibration to the driver; and the dry run brings tool_controller up with the rest and checks /joint_states names the five joints and nothing else.