diff --git a/GEMINI.md b/GEMINI.md
index 836454617e..734aa4eb64 100644
--- a/GEMINI.md
+++ b/GEMINI.md
@@ -52,6 +52,10 @@ powerful tool for developers.
 
 ## Development Conventions
 
+- **Legacy Snippets:** `packages/core/src/prompts/snippets.legacy.ts` is a
+  snapshot of an older system prompt. Avoid changing the prompting verbiage to
+  preserve its historical behavior; however, structural changes to ensure
+  compilation or simplify the code are permitted.
 - **Contributions:** Follow the process outlined in `CONTRIBUTING.md`. Requires
   signing the Google CLA.
 - **Pull Requests:** Keep PRs small, focused, and linked to an existing issue.