diff --git a/docs/superpowers/specs/2026-10-07-scope-features-design.md b/docs/superpowers/specs/2026-10-07-scope-features-design.md
index d80f083..fd4dbc1 100644
--- a/docs/superpowers/specs/2026-10-07-scope-features-design.md
+++ b/docs/superpowers/specs/2026-10-07-scope-features-design.md
@@ -165,8 +165,14 @@ for the same reason every readout in this app quotes a stored sample: t0 has to
 buffer holds, because the cut is a binary search over the time ring and the axis is pinned to
 what the cut got.
 
-A `Window` condition with `level == level2` degrades to an edge on that level, and must — a
-band of zero width is not a special mode.
+**A zero-width band is refused by the panel, not special-cased in the detector.** The band test
+is `v >= lo && v <= hi` and the event is a change of side, so with `level == level2` the signal
+is "inside" only on exact float equality — which a crossing essentially never lands on, making
+the condition one that silently never fires. That is a worse failure than a refusal, and it
+cannot be fixed by special-casing the detector into an edge trigger: the two state machines
+answer different questions and conflating them is the divergence this design exists to prevent.
+So the second level spin is clamped to differ from the first by at least its own increment, the
+panel says why, and `EventDetector` keeps one unconditional band test.
 
 ### Panel and session