Hey cackling.fiend, I figured out how to fix this code-wise. I came looking since I just started a new Lignumis playthrough and couldn't get it to connect to the steam assembling machine.
So it turns out a filtered fluid box and a filtered fluid box with a temperature constraint are not considered equal as far as the game's 2.1 engine is concerned (since hypothetically the unconstrained fluidbox could output a fluid unacceptable to the constrained one). Most steam sources (including your dessication furnaces) don't have fluidbox temperature constraints, but your steam assembler does.
I tried editing your mod by commenting out lines 89 and 90 in steam-assembling-machine.lua (removing minimum_temperature and maximum_temperature), and it fixed being able to connect it to the steam pipe network. Alternatively you could add those constraints to every other steam-related building but honestly that might cause other issues...
assembling_machine.energy_source = {
type = "fluid",
scale_fluid_usage = true,
effectivity = 1,
fluid_box = {
filter = "steam",
production_type = "input",
pipe_picture = machinepipes(),
pipe_covers = pipecovers(),
volume = 50,
pipe_connections = {
{ flow_direction = "input-output", direction = defines.direction.west, position = { -1, 0 } },
{ flow_direction = "input-output", direction = defines.direction.east, position = { 1, 0 } }
},
secondary_draw_orders = { north = -1 },
--minimum_temperature = 100,
--maximum_temperature = 500
}
}
