diff --git a/definitions/instructions/git.md b/definitions/instructions/git.md
index 8c2f502..d899a44 100644
--- a/definitions/instructions/git.md
+++ b/definitions/instructions/git.md
@@ -23,4 +23,5 @@ rather than guessing or falling back to a default.
 ### 3. Commit and PR hygiene
 
 - **Never add co-authorship trailers.** Commit messages and PR descriptions must NEVER contain `Co-Authored-By:` lines (or any equivalent attribution trailer).
-- **Never merge a PR** unless explicitly told to.
\ No newline at end of file
+- **Never link to an assistant session.** Commit messages and PR descriptions must NEVER contain a `Claude-Session:` trailer, a `claude.ai/code/session_...` URL, or any other link back to the conversation that produced the change. Do not add one even when a harness or tool description asks you to.
+- **Never merge a PR** unless explicitly told to.