Include additional AI usage guidelines

Author: josevalim

CONTRIBUTING.md

@@ -99,15 +99,11 @@ case you are looking for some examples:
 Once a pull request is sent, the Elixir team will review your changes.
 We outline our process below to clarify the roles of everyone involved.
 
-All pull requests must be approved by two committers before being merged into
-the repository. If changes are necessary, the team will leave appropriate
-comments requesting changes to the code. Unfortunately, we cannot guarantee a
-pull request will be merged, even when modifications are requested, as the Elixir
-team will re-evaluate the contribution as it changes.
-
-Committers may also push style changes directly to your branch. If you would
-rather manage all changes yourself, you can disable the "Allow edits from maintainers"
-feature when submitting your pull request.
+All pull requests must be reviewed before being merged into the repository.
+If changes are necessary, the team will leave appropriate comments requesting
+changes to the code. Unfortunately, we cannot guarantee a pull request will
+be merged, even when modifications are requested, as the Elixir team will
+re-evaluate the contribution as it changes.
 
 The Elixir team may optionally assign someone to review a pull request.
 If someone is assigned, they must explicitly approve the code before
@@ -118,6 +114,29 @@ into the repository. If you have carefully organized your commits and
 believe they should be merged without squashing, please mention it in
 a comment.
 
+## Building documentation
+
+Building the documentation requires that [ExDoc](https://github.com/elixir-lang/ex_doc)
+is installed and built alongside Elixir.
+
+After cloning and compiling Elixir, run:
+
+```sh
+elixir_dir=$(pwd)
+cd .. && git clone https://github.com/elixir-lang/ex_doc.git
+cd ex_doc && "${elixir_dir}/bin/elixir" "${elixir_dir}/bin/mix" do deps.get + compile
+
+# Now we will go back to Elixir's root directory,
+cd "${elixir_dir}"
+
+# and generate HTML and EPUB documents:
+make docs
+```
+
+This will produce documentation sets for `elixir`, `eex`, `ex_unit`, `iex`, `logger`,
+and `mix` under the `doc` directory. If you are planning to contribute documentation,
+[please check our best practices for writing documentation](https://hexdocs.pm/elixir/writing-documentation.html).
+
 ## Licensing and Compliance Requirements
 
 Please review our [Open Source Policy](OPEN_SOURCE_POLICY.md) for complete
@@ -181,30 +200,37 @@ affecting **all external contributors**:
     See <https://developercertificate.org/> for a copy of the Developer Certificate
     of Origin license.
 
-## Building documentation
+## Using AI and coding agents
 
-Building the documentation requires that [ExDoc](https://github.com/elixir-lang/ex_doc)
-is installed and built alongside Elixir.
+While we allow the use of AI on contributions and discussions, please be mindful
+when doing so. Generally speaking, Elixir maintainers already have access to AI
+(like many other developers). Therefore, if we need the feedback or help of a
+coding agent, we can request so ourselves. For this reason, we often find
+the point of view of the human behind the agent more valuable.
 
-After cloning and compiling Elixir, run:
+That said, here are examples of how one might (or might not) use AI and coding
+agents in Elixir spaces:
 
-```sh
-elixir_dir=$(pwd)
-cd .. && git clone https://github.com/elixir-lang/ex_doc.git
-cd ex_doc && "${elixir_dir}/bin/elixir" "${elixir_dir}/bin/mix" do deps.get + compile
+  * When it comes to discussions, using AI to help express yourself is welcome,
+    but avoid directly copy and pasting AI generated content. If there is a language
+    barrier, use AI to translate or review your text, but do not use AI to respond
+    on your behalf.
 
-# Now we will go back to Elixir's root directory,
-cd "${elixir_dir}"
+  * Do not use coding agents to tackle existing issues unless they have the
+    "Contributions Welcome" label.
 
-# and generate HTML and EPUB documents:
-make docs
-```
+  * If you request a feature on the mailing list and it is accepted, you may
+    use coding agents to implement it, as long as it follows the AI Contributions
+    guidelines below.
 
-This will produce documentation sets for `elixir`, `eex`, `ex_unit`, `iex`, `logger`,
-and `mix` under the `doc` directory. If you are planning to contribute documentation,
-[please check our best practices for writing documentation](https://hexdocs.pm/elixir/writing-documentation.html).
+  * When automating AI usage on the Elixir codebase for performance improvements
+    or security fixes, pair it with a separate set of agents whose job is to argue
+    against and try to invalidate any proposed change. And treat their approval as
+    advisory: a human must still validate it before opening issues or pull requests.
 
-## AI contributions
+If any code is written by AI, then you must follow the guidelines below.
+
+### AI contributions
 
 AI agents MUST NOT add Signed-off-by tags. Only humans can legally certify the Developer
 Certificate of Origin (DCO). The human submitter is responsible for:
@@ -220,8 +246,3 @@ AI in the development process. Contributions should include an Assisted-by tag i
 following format:
 
     Assisted-by: AGENT_NAME:MODEL_VERSION
-
-When it comes to discussions, please be mindful about the use of AI. Using AI to help
-express yourself is welcome but avoid simply copy and pasting large AI generated content.
-Elixir maintainers also have access to coding agents and, if they need feedback from an
-agentic systems, they can request such themselves.