Good news! The Wolfram team has worked extremely quickly and accepted the paclet submission:

https://resources.wolframcloud.com/PacletRepository/resources/MarcoThiel/MMAMixedEffects/

I have learnt two things:

1) The Wolfram team is great! 2) The design of the Wolfram Language and the entire infrastructure is fantastic.

As mentioned before, this has been done with Codex (and Claude). I am transitioning more and more to a workflow where the Wolfram Language is a tool for my AI agents rather than only for me. I still love programming in the Wolfram language, but I would not have had time to write this paclet.

Here is another interesting observation: I did not actually submit the paclet - it was submitted by Codex because of a poorly written prompt of mine. I told it that I wanted to submit the paclet, but had never done that before and needed information. It collected information, downloaded template files, filled them in, and kept going. I went about my normal work. Then I got an email from the Wolfram team that the paclet had been accepted. Codex completed the process. I had said "I want to submit" and thought it would give me the material to submit. Instead it did the entire submission for me. That also shows how well designed the Wolfram system is.

But not all is perfect. Upon trying the paclet. I noticed a minor issue with the installation. Currently you need to do this:

PacletInstall["MarcoThiel/MMAMixedEffects"]
Get[FileNameJoin[{PacletObject["MarcoThiel/MMAMixedEffects"]["Location"], "Kernel", "init.m"}]]
Needs["MarcoThiel`MMAMixedEffects`"]

to make it work. I have a fix ready to submit.

Good news!

The Wolfram Team is as always very helpful and fast. THANKS TO ALL OF YOU!

They have now accepted the paclet submission. It is available at: https://resources.wolframcloud.com/PacletRepository/resources/MarcoThiel/MMAMixedEffects/

Two things:

1) They were really fast. I really appreciate it. 2) I am getting more and more convinced that the Wolfram Language and the entire infrastructure is absolutely great for LLMs.

I am giving more and more Wolfram interaction rights to my agents. Here is what happened with the paclet submission. I had never submitted a paclet before. I told Codex that I wanted to submit this and needed more information about the process and the files to prepare. It went about it, used its browser, downloaded files, filled them in, and apparently finished the submission on its own. I had only planned to get all info I needed, but did not supervise it as I was working on other things.

When - after a couple of hours - I checked my email, the Wolfram team had accepted the submission. Their system is so well designed that it is intuitive enough for an agent. I am in awe.

Thank you again for everything!

PS: The local install works, but ,of course, not all is perfect. I noticed an issue with the paclet install. I have submitted a fix. Until then a temporary workaround is:

PacletInstall["MarcoThiel/MMAMixedEffects"]
Get[FileNameJoin[{PacletObject["MarcoThiel/MMAMixedEffects"]["Location"], "Kernel", "init.m"}]]
Needs["MarcoThiel`MMAMixedEffects`"]

So the Get command will fix it.