Add AGENTS.md

[Gedochao]

Some context for speeding up agents, encouraging certain behaviours and such.

Requires/includes:

• Add LLM policy & a PR template #4177

Checklist

• tested the solution locally and it works
• ran the code formatter (scala-cli fmt .)
• ran scalafix (./mill -i __.fix)
• ran reference docs auto-generation (./mill -i 'generate-reference-doc[]'.run)

How much have your relied on LLM-based tools in this contribution?

extensively, this is made by agents for agents, purely vibe coded metaprompting ™️
used Cursor with Claude

How was the solution tested?

I use this as context for agents when working with this repo and it works reasonably well

Additional notes

A similar file in the Scala 3 repo (without the detailed one)
https://github.com/scala/scala3/blob/main/AGENTS.md

[bishabosha]

where is AGENTS_DETAILED.md recommended?

[Gedochao]

@bishabosha recommended?
As a best practice, tbh I haven't encountered this division, although both documents seem to be useful to me depending on what I do.
Open to suggestions, of course.

[bishabosha]

my thought was that AGENTS.md is hardcoded to be used as context by those agents that support it, so it isnt useful to have a separate file that they arent looking for, perhaps im wrong.

[Gedochao]

After some experiments and research, it seems it will still be handled better by many tools to just have a single file.
One can create summaries when needed on one's own, I suppose.
@bishabosha I suppose I yield.

[He-Pin]

Let agents fix all the issues:)

[Gedochao]

Let agents fix all the issues:)

If only it were that simple. 😅