diff --git a/AGENTS.md b/AGENTS.md
index ff5f4317..3ada3736 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -38,4 +38,10 @@ When creating issues:
 - Keep answers short and concise
 - No emojis in commits, issues, PR comments, or code
 - No fluff or cheerful filler text
-- Technical prose only, be kind but direct (e.g., "Thanks @user" not "Thanks so much @user! 🎉")
+- Technical prose only, be kind but direct (e.g., "Thanks @user" not "Thanks so much @user!")
+
+## Changelog
+- New entries ALWAYS go under `## [Unreleased]` section
+- NEVER modify already-released version sections (e.g., `## [0.12.2]`)
+- Each version section is immutable once released
+- When releasing: rename `[Unreleased]` to the new version, then add a fresh empty `[Unreleased]` section
diff --git a/README.md b/README.md
index bac8f593..67414f34 100644
--- a/README.md
+++ b/README.md
@@ -76,7 +76,8 @@ Complete release process:
    ```bash
    # Change [Unreleased] to the new version number with today's date
    # e.g., ## [0.7.16] - 2025-11-17
-   # Then add a new empty [Unreleased] section at the top
+   # NEVER add entries to already-released version sections
+   # Each version section is immutable once released
    ```
 
 4. **Commit and tag**: