From the changelog, I noticed this snippet
- Added hardened wall as upgrade for concrete wall from concrete wall by Clippy if enabled

The issue is that I'm currently using Clippy's concrete wall mod, and hardened walls are actually being requested when trying to craft hardened walls, only regular walls, despite
elseif mods["ConcreteWall"] then
data.raw["wall"]["stone-wall-2"].next_upgrade = "hardened-wall"
else
data.raw["wall"]["stone-wall"].next_upgrade = "hardened-wall"

I don't understand what the issue may be at a glance, given the fact that both mod and item IDs match, but the statement is not getting called for concretewall and even with the mod installed, it still asks for regular walls.

I'm afraid I don't know what the issue at hand might be, or how to fix it, but I hope you could look into it if possible, because it's an interesting integration.
Thank you in advance.

The issue seems to be that "next_upgrade" is for fast replace and the upgrade planner, not telescopic recipes, like in this case, so it's a code issue. That would imply that these edits also apply to AAI walls.
Sorry for the doublepost while editing.

from what I'm understanding is that you are seeing that the Concrete wall not being in the recipe for Hardened Wall is the issue?

if so, then you are correct. I do not have code in place to change the recipe. It was only meant as a placement upgrade.

I'll update this feature soon - wanting to get hands on with 2.0 and Space Age first - but its on the list now. Sorry for your inconvenience :(

i decided to use this mod as a learning experiment with Git. i have made the requested changes :)

Let me know what you think

Thank you so very much! And no worries at all, that's on me: I thought that was the the default intended interaction instead of only the placement upgrade, my bad.

I'm very thankful for the changes :)