diff --git a/09 - Audits/Activity Log.md b/09 - Audits/Activity Log.md
index dab6d76..57c4aef 100644
--- a/09 - Audits/Activity Log.md	
+++ b/09 - Audits/Activity Log.md	
@@ -11,6 +11,16 @@ entries on top. Maintained by agents per the rule in `../AGENTS.md`.
 
 ---
 
+### 2026-06-07 — frontend@607587c, backend@189b0ab — frontend Docker Yarn install hardening
+
+**Commits:** `607587c` `189b0ab`
+**Touched:** frontend `Dockerfile`, `package.json`; backend `package.json`, `package-lock.json`; docs `09 - Audits/Activity Log.md`
+**Why:** The frontend production Docker build failed in the dependency install layer with `@sentry/cli` / Yarn `ETXTBSY` while unpacking executable files. The Dockerfile now activates the exact Yarn version in its own Corepack layer and serializes the shared BuildKit Yarn cache with a Yarn mutex during `yarn install`.
+**Verification:** frontend isolated BuildKit dependency-layer build using the production install command passed through `[5/5] Building fresh packages` without the `ETXTBSY` failure; frontend `git diff --check -- Dockerfile package.json`; backend `git diff --check -- package.json package-lock.json`; version metadata reads `2.9.27` in both repos. Pushed to Forgejo; `origin` skipped.
+**Linked docs updated:** None
+
+---
+
 ### 2026-06-07 — backend@38d0e76, frontend@051681f — DB audit C6 notification user FK
 
 **Commits:** `38d0e76` `051681f`