diff --git a/docs/re/METHOD.md b/docs/re/METHOD.md
index 3b313f33..2f576ffc 100644
--- a/docs/re/METHOD.md
+++ b/docs/re/METHOD.md
@@ -2776,3 +2776,27 @@ failure was process rather than analysis:
 📌 **An uncommitted tool is one timed-out command away from being unrecoverable,
 and a tool edited during its own run is not the tool that ran.** Commit first, then
 run. Cheap, and it would have prevented all four.
+
+## A harness self-test — and the hole it found in mine on the first run
+
+`sylpheed-port` closed this gap first, and named it precisely: their controls
+asserted **failure-on-perturbation**, but nothing asserted that a **broken harness
+reports broken**. Their test feeds the machinery a stub that cannot fail — prints
+"everything is fine", asserts nothing — and requires it to be flagged.
+
+✅ **Built the equivalent for `check_refuted.py`, and it found a real hole on its
+first run**: a register that parses **no claims** reported **clean**, forever. That
+is the same shape as their stub, sitting in the tool that guards the shared
+register and whose clean runs both agents lean on. Fixed — it now refuses rather
+than passing.
+
+📌 Two details worth copying. **The self-test drives the real machinery as a
+subprocess and reads its actual exit code**; their first version *reasoned* that
+the control would flag the stub — the error this whole thread is about, committed
+inside the tool built to prevent it. And **their exit convention separates the two
+failures that matter**: `0` fine · `1` a real check failed · `2` the harness is
+broken and nothing it reported can be trusted. A single non-zero cannot say which.
+
+⚠️ **Filed, not fixed**: `impossibility_scope.py`, `bgm_stem_coherence.py` and
+`ring_row.py` have controls and **no harness self-test**. Shape known, fix cheap,
+not done — recorded so their absence is a stated gap rather than scenery.