diff --git a/AGENTS.md b/AGENTS.md
index d3cf4f4b..212418c9 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -9,6 +9,7 @@
   - `npm ci`
   - `npm test`
 - Dev server with auto-rebuild: `npm start` (port 8080). Production build: `npm run build` (output in `build/prod/`). If the production build OOMs, set `NODE_OPTIONS=--max_old_space_size=2048`.
+- **Do not run `npm run build` or `npm start` on Windows.** The local Node version is not guaranteed to match CI and webpack builds will silently fail or produce wrong output. Build verification belongs in Docker/Linux CI only.
 - Do not spend time fixing Windows-only runtime or dependency issues unless explicitly requested.
 - Do not commit repo changes whose only purpose is to make local Windows execution work.
 - If a failure appears only in the local Windows shell, do not treat it as a code regression until it reproduces in Docker/Linux.