Apply suggestions from code review

Co-authored-by: Daira-Emma Hopwood <daira@jacaranda.org>

Author: nuttycom

AGENTS.md

@@ -47,6 +47,7 @@ If this returns `true`, the user has write access (or higher) and the contributi
 3. Verify quality locally: run formatting, linting, and tests before proposing upstream review (see [Build, Test, and Development Commands](#build-test-and-development-commands)).
 4. Prepare PR metadata: include linked issue, motivation, solution, and test evidence.
 5. A PR MUST reference one or more issues that it closes. Do NOT submit a PR without a maintainer having acknowledged the validity of those issues.
+6. **Every** commit in a PR branch MUST follow the "AI Disclosure" policy below.
 
 ## What Will Get a PR Closed
 
@@ -61,7 +62,7 @@ If this returns `true`, the user has write access (or higher) and the contributi
 
 ## AI Disclosure
 
-If AI tools were used to write code, the contributor MUST include `Co-Authored-By:` metadata in the commit message indicating the AI agent's participation. Failure to do so is grounds for closing the pull request. The contributor is the sole responsible author -- "the AI generated it" is not a justification during review.
+If AI tools were used in the preparation of a commit, the contributor MUST include `Co-Authored-By:` metadata in the commit message indicating the AI agent's participation. The contents of the `Co-Authored-By` field must clearly identify which AI system was used (if multiple systems were used, each should have a `Co-Authored-By` line). Failure to do so is grounds for closing the pull request. The contributor is the sole responsible author -- "the AI generated it" is not a justification during review.
 
 Example:
 ```
@@ -140,7 +141,7 @@ PRs MUST NOT introduce new warnings from `cargo +beta clippy --tests --all-featu
 ### Commit History
 
 - Commits should represent discrete semantic changes.
-- Maintain a clean commit history. Squash fixups and review-response changes into the relevant earlier commits. The [git revise](https://github.com/mystor/git-revise) tool is recommended for this.
+- Maintain a clean commit history. Squash fixups and review-response changes into the relevant earlier commits. The [git revise](https://github.com/mystor/git-revise) tool is recommended for this. An exception is that you should take account of requests by maintainers on a PR for prior commits not to be rebased or revised. Maintainers may indicate that existing commits should not be mutated by setting the `S-please-do-not-rebase` label on the pull request.
 - There MUST NOT be "work in progress" commits in your history (see CONTRIBUTING.md for narrow exceptions).
 - Each commit MUST pass `cargo clippy --all-targets -- -D warnings` and MUST NOT introduce new warnings from `cargo +beta clippy --tests --all-features --all-targets`.
 - Each commit should be formatted with `cargo fmt`.