It seems that the Python Matter server needs custom code for every device with a Matter custom cluster.
Is there any chance of Home Assistant getting some kind of auto-discovery for this? If I understand correctly, every Matter device implement a descriptor cluster with attribute, accepted command, and generated command lists.
Home Assistant offers a vision of the smart home based on entities that hides the specifics of each protocol. That’s a common set of features, actions, etc. like a light that can be turned on or off or adjust brightness and you don’t care if the light is Matter, Zigbee, cloud based or uses a proprietary API. That’s the model, SmartThings calls them capabilities, Google Home calls them traits.
The problem with custom clusters is that you don’t even know how they work or what they do, or what attributes you’re supposed to write, or if you are supposed to poll them or what. If the Matter server or the integration doesn’t know that certain attribute means the active power in watts, it can’t associate it to an entity or present it to the user interface in a useful way.
That happens even with standard functions, there’s a lot of Matter features (commands and attributes of standard clusters) not exposed to Home Assistant and it’s a pity.
It would be great if you could (easily) call standard commands directly from automations, like Move / Stop for continuous dimming of a light until stopping or OnWithTimeOff for the native auto-off that runs in the smart plug. Kind of what Flic does with their Flic Script for their buttons where you can assign as action a Matter command.