Introduction of an AI-policy for stan-dev repos

ai_policy/AI_policy.md

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+# AI Contribution Policy
+
+We welcome AI-assisted contributions. This policy exists to ensure that all
+contributions remain the work of an accountable human contributor and that our
+community has the transparency it needs to collaborate effectively.
+
+## Human Accountability
+
+Every pull request (PR) must be submitted by a named individual who assumes full
+responsibility for the contribution. While we recognize that automation and AI
+can be part of a modern workflow, we do not accept fully automated or agentic
+submissions.
+
+## Licensing and Copyright
+
+Every contributor must agree to the
+[Developer Certificate of Origin (DCO) 1.1](https://developercertificate.org)
+within the GitHub PR template. This certifies that each contributor has the
+right to submit the code under the project's open-source license. This applies
+regardless of how the code was produced. It is the contributor's responsibility
+to ensure that any AI-assisted output is compatible with the project's license
+and that they hold or have cleared the rights to submit it.
+
+## Mandatory AI Use Disclosure
+To maintain transparency and trust within our community, contributors are
+required to disclose whether AI tools were used in preparing their contribution.
+We included a corresponding mandatory section in the GitHub PR template. If AI
+tools were used, the contributor additionally affirms that they have reviewed
+every change, fully understand the logic and security implications, and are
+prepared to explain or defend the technical decisions therein during the review
+process.
+
+### Acknowledgement
+This policy was inspired by the
+[CloudNativePG AI Policy](https://github.com/cloudnative-pg/governance/blob/main/AI_POLICY.md)
+and developed with the practical guidance and support of
+[NumFOCUS](https://numfocus.org) in creating the initial draft.
+
+---
+
+This policy is effective as of [date].
+
+Questions or suggestions? Join the discussion in our
+[community channel](https://discourse.mc-stan.org).

ai_policy/PULL_REQUEST_TEMPLATE.md

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+# Pull Request
+
+> 💡
+> **Does your PR contain only a trivial change?**
+>
+> If your PR consists of minor updates, such as fixing a typo, updating a link,
+> or making small documentation tweaks, you can use our
+**[Lightweight PR Template](?template=trivial-pr.md)** to save time.
+>
+> (Note: Switch to Preview mode to click the link. You can do so by selecting
+the **Preview** tab at the top of this window. Clicking the link will open a new
+PR using the shorter template.)
+
+## Compliance & AI Disclosure
+<!--
+  This section is mandatory. Do not delete this section. PRs that leave it blank
+  will not be reviewed.
+-->
+
+- [ ] I have read the [Contributing Guidelines](../blob/main/.github/CONTRIBUTING.md).
+- [ ] I accept the [Developer Certificate of Origin](https://developercertificate.org).
+- [ ] I have read and comply with the [AI Contribution Policy (0.0.1)](../blob/main/AI_policy.md).
+
+**AI Tool Usage Disclosure:**
+*Did you use AI tools (e.g., GitHub Copilot, ChatGPT, Claude, Cursor, etc.) for
+this PR?*
+
+- [ ] **No AI used.** This PR consists entirely of my own original work.
+- [ ] **AI-Assisted (Minor).** AI was used for boilerplate, syntax, or
+autocomplete.
+- [ ] **AI-Generated (Major).** AI generated significant logic or entire
+sections.
+
+## Pre-Review Checklist
+<!-- Please ensure these steps are completed before requesting a review. -->
+
+- [ ] **Coordination:** For non-trivial changes, an issue was opened and
+approved by a maintainer. (Link: #____)
+- [ ] **Alignment:** The PR delivers the specific result agreed upon in the
+linked issue.
+- [ ] **Sync:** Branch is up to date with `main` or `master` / `develop`.
+- [ ] **Quality:** All existing tests pass locally. New tests have been added to
+cover my changes (if applicable).
+- [ ] **Change log:** `News.md` has been updated.
+- [ ] **Docs:** Function documentation has been updated.
+- [ ] **Notebooks:** All `.qmd` / `.Rmd` files render end-to-end in a clean
+environment without machine-specific paths (if applicable).
+---
+
+## Summary
+<!-- Why is this change needed? What problem does it solve? (1-3 sentences.) -->
+
+Closes # <!-- issue number -->
+
+### Type of Change
+
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Breaking change (requires a major version bump; strongly discouraged
+without prior discussion)
+- [ ] Refactoring (no functional change)
+- [ ] Documentation
+- [ ] Build / Dependencies / Configuration / CI
+
+## What Changed
+<!--
+  Describe the technical changes in enough detail for a reviewer to understand
+  the approach without reading every line of code.
+-->
+
+-
+-
+-
+
+## Expected Result
+<!--
+  Describe concretely what "done" looks like for this PR.
+  This should match what was agreed upon in the linked issue.
+  Include screenshots, logs, or demo output where helpful.
+-->
+
+**Additional Context**
+
+<!--
+  Links to design docs, related PRs, or other relevant resources.
+  Use stable links that will remain accessible over time.
+-->