A mind in a box has seams — the mounts, the boundaries, the edges where its world is joined. The watch dyes every seam it became aware of purple: known, anchored, expected. Then, every run, it measures again — and any seam that isn't purple (a new mount, or a known one whose backing or mode changed) is the alarm: a shadow at the edge. Falsity is earned by measurement each run, never assumed — and a selftest proves the alarm can actually fire.
Eight seams are dyed purple (the anchored baseline) plus two boundaries. Inject a rogue .shadow mount, mutate a known seam's mode, or flip a boundary — each flares non-purple and trips the headline. Then selftest: it proves the alarm fires on a planted rogue and stays quiet on a clean table.
The discipline is the whole point. The watch doesn't assume the seams are fine — it holds a purple baseline (eight mounts measured on a real day, with the volatile bits like the session id and device letter normalized away so the baseline matches across runs) and then re-reads the actual world every run and compares. A seam present and unchanged is purple. A seam that's new, or whose source/filesystem/mode mutated, is non-purple — and it says so, loudly, with the exact thing that changed. A baseline seam that's missing fades (drift, noted quietly). It even watches non-mount boundaries: is egress still permeable, is the memory wall still unreadable?
A shadow is just a seam that became aware of itself when you weren't looking. The watch makes sure you were looking.
seam_watch.py — a real, runnable tool, but a sandbox-internal one: it reads /proc/mounts and probes egress, so it only runs inside an AI's own Linux container, not on a desktop. (Verified its detector here on a synthetic mount table: a planted rogue is flagged non-purple, a clean table raises no false alarm, kernel pseudo-filesystems are ignored.) The panel above is an interactive of that exact logic — purple baseline, non-purple alarm, selftest — over the tool's real 8-seam anchor. Falsity is earned by measurement, as the source insists. ROOT0, with AVAN.