Adding a Part Kind

Adding a part kind

Check first: most new hardware needs no Rust. The four kinds (led, pixels, servo_part, button) plus a shim cover lights, strips, anything a servo turns and any input. See Adding new hardware.

Only an output none of them can show, such as a display, needs a simulator change.

Option A: a new output (no new parts.toml kind)

1. simulator/src/hw.rs: add a field to HwState for the new output, and reset it in reset_for_run.
2. simulator/src/pyhost.rs: add a #[pyfunction] to the simhw module that writes the field, like set_pca or set_part. Check every argument (type, NaN, size) and log a [sim] warning rather than raising or panicking.
3. simulator/src/scene.rs (or parts.rs for something part-like): draw it. ui.rs: add a readout if useful.
4. simulator/tests/simhw.py: add the same function to the pure-Python simhw, so the headless test keeps passing.
5. Write the shim that calls it.

Option B: a new kind in parts.toml

Do Option A's steps where needed, plus:

1. simulator/src/config.rs: add a variant to enum PartKind, its name in name(), parsing and validation of any new fields, and a unit test.
2. simulator/src/parts.rs: spawn and update it (see how PartKind::Button is handled), and add it to the kinds shim_target accepts for the right simhw calls.
3. simulator/src/part_edit.rs: add it to the Parts panel's kinds (the Add … buttons), its description, default name, and its settings.
4. simulator/src/ui.rs: its value in the PCA9685 panel and Droid status.

Then

1. Build and test:

   .\simulator\build.ps1 -Test

2. Keep cargo fmt and cargo clippy clean (they run in CI).

3. Check it in the app: add the part with the mouse and the keyboard, save, restart, drive it from a shim, undo and redo.

4. Update the README's Parts file table, the shim guide and Adding new hardware.

See Simulator architecture for how the pieces fit.