…so, turns out that to attach a steamgun to the mecharachnid's tail, you have to transfer it from the player's inventory to the mecharachnid's inventory, switch control to the mecharachnid, and use the mecharachnid's Tail Attachment talent. Because that's not at all convoluted or annoying.

v1a thus adds a new action to the Interact with the Mech chat dialog to access the tail mount. (This required a bit of deep hackery, as the Tail Attachment talent isn't expecting to have to deal with someone else's inventory, but sometimes I like a challenge.

)
And as long as I was in the neighborhood, I added a few more small things that were bugging me:
- I always forget when my mecharachnid has new talent points to spend, either because I increased my Mecharachid Chassis talent level or because I switched chassis and haven't spend the points in the new chassis yet. So the new release prints a log message as a reminder, similar to the one the player gets on level-up.
- This one I think is a bug: If your mecharachnid is using, say, the Armament chassis, and you switch it to Assault when it has no steamsaws in inventory to switch the tail mount to, it will leave the current steamgun mounted, which just seems ripe for problems. The new release detects this case and unmounts the mismatched tail weapon.