add a probe that shows what the gamepad is doing

The axis and button indices in mapping.py are SDL's documented layout rather
than an observed one, and until now the only way to find a pad that numbers
things differently was to watch a real arm move the wrong way.

`dora-teleop-probe` prints the raw axes, the buttons it sees and the velocity
that would be sent, live, with no dataflow and no arm — it cannot move anything.
It goes through the same Gamepad and velocity() the node runs, so what it prints
is what the arm would get; that is the whole reason it is worth having, and the
reason it must not grow its own copy of the mapping.

Every axis is listed, including ones the layout does not use, because an axis
marked unused that moves when a stick is pushed is exactly the finding this is
for. The centred bar makes a worn stick that does not return to zero obvious.

dora_teleop/probe.py

@@ -0,0 +1,132 @@
+"""Show what the pad is doing, with no dataflow and no arm.
+
+`dora-teleop-probe` opens the gamepad and prints, live: the raw axes SDL
+reports, the buttons it sees pressed, and the velocity this node would send.
+
+It exists because the axis and button indices in :mod:`dora_teleop.mapping` are
+SDL's documented layout rather than an observed one, and a pad that disagrees is
+otherwise discovered by watching a real arm move the wrong way. It goes through
+:class:`~dora_teleop.gamepad.Gamepad` and :func:`~dora_teleop.mapping.velocity`
+— the same code the node runs — so what it prints is what the arm would get.
+
+Nothing here can move anything. There is no dora node and no connection to the
+arm; this only reads.
+"""
+
+import argparse
+import time
+
+from dora_teleop import mapping
+from dora_teleop.config import Config
+from dora_teleop.gamepad import Gamepad
+from dora_teleop.mapping import LAYOUT
+
+# What each velocity component is, in the order the arm takes them.
+COMPONENTS = (
+    ("vx", "mm/s", "forward / back"),
+    ("vy", "mm/s", "left / right"),
+    ("vz", "mm/s", "up / down"),
+    ("wx", "deg/s", "roll"),
+    ("wy", "deg/s", "pitch"),
+    ("wz", "deg/s", "yaw"),
+)
+
+CLEAR = "\033[H\033[J"
+
+
+def axis_names(layout=LAYOUT) -> dict[int, str]:
+    """Name each axis index the layout uses."""
+    return {
+        layout.left_x: "left stick X",
+        layout.left_y: "left stick Y",
+        layout.left_trigger: "left trigger",
+        layout.right_x: "right stick X",
+        layout.right_y: "right stick Y",
+        layout.right_trigger: "right trigger",
+    }
+
+
+def button_names(layout=LAYOUT) -> dict[int, str]:
+    """Name each button index the layout uses."""
+    return {
+        layout.grasp: "grasp",
+        layout.release: "release",
+        layout.clear: "clear",
+        layout.freedrive: "freedrive",
+        layout.yaw_left: "yaw left",
+        layout.yaw_right: "yaw right",
+        layout.estop: "E-STOP",
+    }
+
+
+def bar(value: float, width: int = 21) -> str:
+    """Draw a centred bar for a value between -1 and 1.
+
+    Seeing the bar sit off-centre with the stick released is how a worn pad
+    announces itself, which is most of the point of looking at raw numbers.
+    """
+    middle = width // 2
+    position = middle + round(max(-1.0, min(1.0, value)) * middle)
+    cells = ["-"] * width
+    cells[middle] = "|"
+    cells[position] = "#"
+    return "".join(cells)
+
+
+def render(sample, velocity: list[float], config: Config) -> str:
+    """Build the whole display for one reading."""
+    lines = ["dora-teleop probe — Ctrl-C to stop", ""]
+
+    if not sample.present:
+        lines += [
+            "  no gamepad found.",
+            "",
+            f"  looking for joystick index {config.joystick_index};",
+            "  plug one in and this will pick it up.",
+        ]
+        return "\n".join(lines)
+
+    names = axis_names()
+    lines.append(f"  axes ({len(sample.axes)} reported)")
+    for index, value in enumerate(sample.axes):
+        name = names.get(index, "unused")
+        lines.append(f"    {index}  {name:<15} {value:+.3f}  {bar(value)}")
+
+    labels = button_names()
+    held = [f"{index}:{labels.get(index, 'unused')}" for index, down in enumerate(sample.buttons) if down]
+    lines += ["", f"  buttons ({len(sample.buttons)} reported)", f"    {', '.join(held) or 'none pressed'}"]
+
+    lines += ["", "  velocity this would send to the arm"]
+    for (name, units, meaning), value in zip(COMPONENTS, velocity, strict=True):
+        marker = "  <--" if value else ""
+        lines.append(f"    {name}  {value:+8.2f} {units:<6} {meaning:<14}{marker}".rstrip())
+
+    moving = "yes" if mapping.is_moving(velocity) else "no — the arm would be told to hold still"
+    lines += ["", f"  moving: {moving}"]
+    return "\n".join(lines)
+
+
+def main() -> None:
+    """Open the pad and print what it is doing until interrupted."""
+    parser = argparse.ArgumentParser(description="Show what the gamepad is doing. Moves nothing.")
+    parser.add_argument("--hz", type=float, default=10.0, help="Redraw rate. Defaults to 10.")
+    args = parser.parse_args()
+
+    config = Config.from_env()
+    gamepad = Gamepad(config.joystick_index)
+    gamepad.start()
+
+    try:
+        while True:
+            sample = gamepad.read()
+            velocity = mapping.velocity(sample.axes, sample.buttons, config) if sample.present else [0.0] * 6
+            print(CLEAR + render(sample, velocity, config), flush=True)
+            time.sleep(1.0 / args.hz)
+    except KeyboardInterrupt:
+        print()
+    finally:
+        gamepad.shutdown()
+
+
+if __name__ == "__main__":
+    main()