chore(next): record generated agent guidance

Author: ericyangpan

AGENTS.md

@@ -36,3 +36,13 @@
 - Match standalone `HOSTNAME` to the preview URL hostname. For `http://localhost:<port>`, use `HOSTNAME=localhost`, never `127.0.0.1`.
 - After each standalone start or restart, verify a default-locale URL, a locale-prefixed URL, and a referenced stylesheet all return `200`, with the stylesheet served as CSS. A tmux start command must include asset sync and the matching `HOSTNAME`.
 - Never create a commit without asking the user first.
+
+<!-- BEGIN:nextjs-agent-rules -->
+
+# This is NOT the Next.js you know
+
+This version has breaking changes — APIs, conventions, and file structure may all differ from your training data. Read the relevant guide in `node_modules/next/dist/docs/` (resolved from this file's directory; in monorepos the `next` package may not be visible from the repo root) before writing any code. Heed deprecation notices.
+
+This block is written and re-added by `next dev` — verify at `node_modules/next/dist/server/lib/generate-agent-files.js`. Removing it from a diff only re-creates the uncommitted change; committing it with your work keeps the tree clean.
+
+<!-- END:nextjs-agent-rules -->