docs: migrate dotfiles agent instructions

AGENTS.md

@@ -1,15 +1,34 @@
-# Repository instructions
+# Alexion's Monorepo
 
 ## Commit convention
 
-Use Conventional Commits for all commit messages.
-Before writing a commit message, read `docs/conventional-commits.md`.
-Do not add agent attribution or co-author trailers.
+- Use Conventional Commits for all commit messages.
+  Before writing a commit message, read `docs/conventional-commits.md`.
+- Keep commit messages about the Git history, not the forge workflow.
+  Include external references only when they are stable context for the change.
+- Do not add agent attribution or co-author trailers.
 
 ## Technical writing
 
-Use `docs/technical-writing.md` and `docs/dictionary.md` for authored prose.
-Use the nearest project dictionary for project-specific domain language.
+- Use `docs/technical-writing.md` and `docs/dictionary.md` for authored prose.
+  Use the nearest project dictionary for project-specific domain language.
+
+## Pull requests
+
+- During pull-request development, add follow-up commits instead of amending existing commits.
+  Preserve review history until the pull request is ready to merge.
+
+## Forge workflow
+
+- Use `gitea-axi` for Gitea issues, pull requests, labels, reviews, comments, and milestones.
+  It resolves this repository from the `origin` remote inside the checkout.
+
+## Tooling
+
+- When a command is missing from the ordinary environment, prefer running it through Nix instead of installing it ad hoc.
+  For example, use `nix shell nixpkgs#python3 -c python3 <script>` for one-off Python commands.
+- Stage new files that Nix discovers through flake evaluation before testing.
+  Flake evaluation ignores untracked files, so auto-loaded modules must be tracked before `nixos-rebuild --flake` can see them.
 
 ## Gotchas