One stage of a sensor module's pipeline.

Mirrors tbp/monty/sensor_modules/sensor_module.py::Transform, which Monty declares as a Protocol so a config can name any callable. Here it is a behaviour, and the sensor module stores each transform as {module, transform} — the module that knows how to call it, and the config that says how.

A transform answers the payload it was given, changed. It may make a percept from the observation, add goals, claim a region, or write telemetry; it may also pass the payload through untouched, which is what a stage for a feature this run does not use does.

Why it also answers itself

Monty's transforms are objects that keep state: a smoothing filter remembers the frames it has seen, a background model remembers the background. In Elixir a struct cannot be mutated, so a transform answers the transform it leaves behind — {payload, transform} — and the sensor module keeps that one for the next step. Same reason samplers answer their stream (docs/monty-differences.md §2.5), and the reason a reset has something to reset (§2.13).