The brain dir is a Syncthing sendreceive folder and Syncthing syncs symlinks; search, vectorstore, context and graph readers follow one out of the brain and would index or return what it points to (reproduced with search.Query). Decision (#157): a tripwire now, brain-wide os.Root readers next. - symlinkguard.Scan lists every symlink inside the brain dir (skipping .git; the brain dir itself may be a mount symlink). - At startup the server refuses to start while any exists, naming them. - symlinkguard.Watch rescans every BRAIN_SYMLINK_SCAN_INTERVAL seconds (default 300) and sends one ntfy alert per new set of symlinks. The live brain dir had 0 symlinks on 2026-10-03, checked before this change, so deploying it does not trip. Refs #157 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>