Your idea sounds fairly intuitive to use, but won't it make attack a lot weaker than defense? Is that desirable?
A question: Do you get these promos from moving through enemy tiles (and/or will they interact with pillage)?
The temp healing promos can be carried anywhere you can get to in 10 turns, so to the player that does not plan, yes they will be weaker on attack. But to the player that does, they can now potentially get the previous friendly heal amount in enemy territory, so they will be stronger if the temp supply promos are tended to and maintained.
Also re attacker strength, or rather defender strength, the existing database features, of which I am pushing the limits here somewhat, does not allow for any easy mechanism for cities to confer supply promos to the units directly, and otherwise only allows for universal healing bonus (remember, naval untouched by any of this and still relies on the old mechanism underlying everything here) -- a city garrison that is unsupported by these promos will only heal 5 hp per turn, but if the promos are present nearby they can still do the usual 20.
Reality is current AI will have no idea how any of this works, and will stumble over much of it on defense but probably far less on attack -- so yes as deployed thus far I would expect a general vibe of weaker attacks, but if something like this ever got proper AI analysis then I'd argue it could be more of a neutral change, weaker distant attacks and stronger towards those nearby the attacker.
Re: enemy tiles, my 1st draft last night I did not enable this, primarily cuz I wanted to encourage the "supply line" idea of units or workers having to move back and forth to owned infrastructure to replenish. Access to enemy improvements could be toggled via database however, it's a very trivial change.
Re: pillage: no change. Database doesn't provide for anything here. Would be relatively trivial to do in Lua, and would thematically make sense that the food supply buff would be gained on pillage, but that will be a future addition, maybe -- for now scope is constrained to database-only changes, as this is a defacto prerequisite for most congress proposals
did you remove the medic promos? otherwise seems they would still work here.
I left the medic promotion and all other healing stuff intact. I'm guessing these would have to be adjusted if this idea is developed further, but for 1st draft seemed fine to leave as-is, it's only gonna result in a free 5 hp heal with medic 1, player will still be encouraged to use the other temp promos in addition. I think the belief that allows extra healing will be a big one that feels much more valuable now. Will need a read on general in-game vibe to determine how exactly they should be adjusted.
Supply lines isn't civ....that's just a different game at that point. Civ is not a combat simulator, it doesn't ever get into the nitty gritties of war.
Yes fair point, however I think there might be some satisfying abstraction here. For example, units could be left to fight in enemy territory as they do now, but with a handful of workers transiting back and forth to keep up the availability of heals in the combat zone. Or a small number of the units themselves could tag back to home territory to collect supplies. No new supply line system, just moving our existing workers and/or our existing units back and forth intermittently.
Forgot to mention recon is excluded in my ruleset, still heal same as before.
Anyway will post here in a few hours, for anyone that wants to test drive, tweak values etc.