Ummm....
*brain fails completely*
Le sigh. I'm gonna have to go back and look at the really old updates to tell you, as well as some of the stuff AN has said to give you a really detailed response.
Suffice to say in a basic sense the Half-Exile system is a system of punishment and redemption first, or at least it is supposed to be.
Whenever someone makes a serious enough crime or pisses off their local patrician/village alderman too hard they can be deemed "spiritually unclean" and then separated from those who are not half-exile. They are then provided with food and shelter sufficient to survive and access to at least one priest and are put to work on unclean tasks like making Black Soil or handling the dead(the half exiles are very tied up in our death taboo). When their overseeing priest deems them to be cleansed of their sins they are released from their status of half exlie and return to normal society.
A couple of big points. It is not inheritable parent to child. It has no defined term limits, you are released when the local priests say you are. Annnd a couple of other things I am forgetting.
Okay, to expand further upon it:
-Half exile grew out of prehistoric plague quarantine practices. The people in quarantine who aren't visibly infected are given a plot of land to work away from the rest of the comunity so if they are contagious nobody gets hit.
--When we first encountered Smallpox, to avoid developing xenophobia, we directed the blame onto disturbing the dead/handling rot. While it's not really the fault of cleanliness, it did help a lot with our other social practices, which ended up giving us a lower level of disease than comparable population densities(imagine if you will, our cities except people aren't obsessively focused on staying clean, developing expensive infrastructure for the sole purpose of washing the unwashed masses).
-When crime started showing up, we needed a punishment below full Exile/Execution, yet society was simply not developed enough to feed criminals for nothing in a penal system(modern penal systems evolved out of incarceration for political prisoners who would have been too dangerous to execute for fear of backlash).
--Thus the Half-exile system, where criminals are considered spiritually tainted and quarantined in much the same way, but assigned corrective labor. As they were already tainted, it was reasoned that this was for the good of the community that the people at risk take more risks, handling corpses and all that.
--Criminals were assigned for a set period of half-exileness, depending on the crime, and released afterwards
-This worked out until we discovered Black Soil while fighting the Tree Blight. This was a job that REQUIRED a certain minimum percentage of the population handling the rubbish and human waste of basically the rest of the population. There was a brief phase where the demand rose to the point that we put EVERYONE on literal shit duty rotation, which led to the early discovery of milling. Then the problem 'went away'.
--We assumed this was because the mills reduced the work needed to crush the ashes. But in reality what happened was that our Harmony and Stewards social traits made it easy to trump up charges, as being disruptive or wasting resources were minor crimes which could see you made half exile for like a week or a month tops.
--This provided a steady supply of teenagers being teenagers, migrants unknowingly breaking the laws, and generally all the brawling and whatnot, filling in the half-exile ranks.
-When we ran into corruption, then, some of our Patricians realized something: You COULD just keep accusing people that nobody else likes of minor crimes, and send them into half exiles to avoid your precious children getting stuck with the job, nobody would care! This also covered for simply not punishing the well connected, the crime rate remains constant, so it never really registered higher up.
-Then as our connectivity stretched thin, increasingly the priests are local priests, taught by their relatives, rather than priests being trained and taught as standard in Sacred Forest. It is then a small step to make it so that repeat criminals, instead of being freed and then accused again, are simply up for the priest to review if they can go on parole. And the priest has reason NOT to pass review, so they will pick on minor disruptive elements to justify spending another week or month in the job.
-At this point, what was supposed to be a primarily temporary sentence with permanent half exile being for heinous crimes not amounting to execution, had become a primarily permanent sentence with hope of parole. This led to several consequences.
--The half exiles, being permanent, tended to have children with other half exiles. These children have no connections, their parents lack useful skills, and they have been taught from childhood that the world is out to get them.
---So they hit their teens, act out, and get slammed with a heavy (theoretically) deterrent sentence, validating their worldview, so that they will vandalize, act out and generally take a "fuck you" perspective, which would flag them as lifetime offenders who keep getting hauled back in, forming a hereditary half exile class.
----And before anyone asks, taking their children away to be raised by the priests and prevent the vicious cycle would probably push them over the edge and go lynch some people.
We actually made a bit of a pushback after developing a sewage system, which dramatically cut the number of half exiles needed for urban waste disposal...but even in the modern day shitty jobs will be needed and nobody wants to root for them when that means THEY have to do said shitty job.
You can't even pay them unpleasantness/hazard pay, these jobs produce no net wealth and too many hands are needed for a sufficient pay package to entice them.
I see... So, conceivably if we went really hard with roads and Black Soil and stuff, we'd end up straining our penal system to the point that we run low on half-exile labor to perform the unpleasant work that our society depends on?
We'd never run low on half-exile labor, there's always more and more trivial crimes.
But roads aren't half exile work. They're a skilled labor.