I have no idea what would be required for coding, but something that could take the hot/cold modifier of the starting planet and have the terraforming send it down a specific route.
This way you could keep the hot/cold modifiers in order to have separate projects for building mirrors/shades if you wanted to do that.
And you couldn't progress beyond a certain point until you build them, or those conditions are saved until last. So you might terraform a hot barren world as far as being arid or jungle, and then get stuck until you build a shade or terraform again to remove the hot condition.
It might also be worth considering a bit of randomness in the terraforming 'outputs'.
The type of a planet doesn't affect it's habitability ouside of the hab category it's assigned to, which is entirely invisible to the player.
You could use the original hot/cold condition to specifiy that a planet could eventually become A, B, C. Or X, Y, Z.
For example:
Your 'worst case' starting conditions would possibly be irradiated.
Terraforming might then change that to barren.
After that it might go to barren desert, and then on to desert.
There it could split depending on the hot/cold in to arid or jungle for hot. And tundra for cold. Terran Eccentric could be a 'wildcard' here.
After that you either get your shade/mirror building above, or just go straight to terran.
So basically: cat_irradiated -> cat_barren -> cat_hab1 -> cat_hab2 -> cat_hab3 -> cat_hab4
There exists a cat_hab5 for 'better than terran' worlds. Not sure if this is currently used or not, but it might be an idea to include it in the possible end results if you want the final output to be terran.
You could also slip in the various other planet types into branches leading in.
So a toxic, volcanic or cryo world might lead into barren, and then on down the chain.
While a frozen world might be a special case where you can't terraform it directly until you build some mirrors to melt all the ice etc. and turn it directly into a water world.
Another possibility to consider is to explicitly
not have terran as the end result.
Instead having terran eccentric as the 'best' result to represent the imperfect technology of the sector.
Or even just stopping at the cat_3 worlds.
This would increase the variety of planet types instead of just having all terrans everywhere, and keep 'natural' terran worlds still being somewhat valuable.
This is all just text on the internet though. Hopefully some of it might even be useful to you.
[e]
Some candidates for the industry image pulled from GIS: