He means the personality type more than the caste. (His roots are green and long enough it's obviously a different color than the rest of his hair.)

Hi, Wrebb engineers! Here is an implausible story, a pocket everything, and an explanation of electricity and mechanics and evolution-at-least-as-it-worked-in-Amenta-who-knows-about-this-place.

The evolution story seems consistent with how animals seem to work. Obviously people are different. The pocket everything is amazing!

Yeah! Why don't they have a stab at lightbulbs and then anyone who pulls lightbulbs off successfully can buy the things that come after lightbulbs from Aitim with the money they make from lightbulbs.

It's a lot of steps from lightbulbs to pocket everythings but most of them are useful in their own right.

Also, how do they send messages with shines, exactly?

Shines can be programmed to go certain distances and then do things! They can be different colors. Here is a chart of code. Shines go from one shine message station to another and then line up to be read.

Yes, the thing he is interested in is the chart of code, Amentans put lots of thought into a related problem and it might be useful. How many shines represent each character? How many characters are there to represent?

Two shines per character. The common has 31 letters and they also have numerals and punctuation, though it's conventional to save time and shines and therefore money to omit and abbreviate a lot.

Aitim is pretty sure someone with relevant experience could improve this a lot but he can't! Are there automata that can read the shines into messages or do people have to do that? How fast do shines travel?

Automata don't have senses, he's thinking of a golem. There could be a golem that did that but they don't have one. Shines go really fast! Really really fast.

At the speed of light?

Well, they're light. So that seems reasonable.

It's actually kind of important for the long term when they want to start colonizing other planets whether it's at the speed of light or not.

Well, how would they tell?

Can you send shines to the sun or get shines from the sun or anything like that? Or the moon?

Shines have to go along surfaces.

In that case it matters significantly less whether they go the speed of light or not. 

Aitim encourages everybody to let him know if they get lightbulbs working and want more.

Eventually somebody has a lightbulb.

Aitim has been spending his free time scouting for soaps that smell nice and continuing to periodically worry off the outer layer of his skin and smiling at cute babies. They are still springing. They might just be stuck that way.

He writes with congratulations on the lightbulb. Here's how you'd scale them.

Lightbulbs!!

There are pleasantly scented soaps and there's running cold water in the creche and a little automaton that does friction-based heating for small amounts of hot water. There is even a laundry automaton.

Aitim spends most of his time taking showers with nice-smelling soaps. 

Heaters should be easy with electricity, he thinks you just run a lot of it through something with a high enough melting point it won't get messed up.

In a while they figure that out.

Then he'll take hot showers. When he has assembled a series of soaps that he likes he will set up a laundry automaton to put all of his clothes through that and he will occasionally give Kalatha long baths with soaps that smell nice and then sit wrapped in fresh-dried sheets with her and sing her Anitami songs.

(Aitim does not remember how sewing machines work; he's pretty sure there's a trick to it, rather than it being a machine sewing the way a person would sew).

Kalatha does not like baths.

Does getting used to playing with water help? Does she like to try to eat the soaps? Is there a water temperature that is more fun?

She eats a soap and is SO UPSET. She can put up with short baths but then she is done.

That is probably within the normal range of variance even for Amentan babies and these people also clearly all have something wrong with them. Kalatha will obviously have baths that are a length she finds acceptable as often as she will tolerate them.