test: tighten waveform-collapse and knob-face rect assertions

Height-3 case pins the halfSpan clamp itself (height-4 passed pre-fix too); dropped the vacuous tall-rect mirror since min() is symmetric and wide already discriminates.

tests/test_component_geometry.cpp

@@ -265,9 +265,14 @@ static void testDegenerateBandClampsHalfSpanToZero() {
     CHECK(waveformBand(0, 3).halfSpan == 0.0);
     CHECK(waveformBand(0, 0).halfSpan == 0.0);
     // A zero half-span collapses every column onto the zero line regardless of amplitude sign.
-    const WaveformBand b = waveformBand(10, 4);
+    // height 3 (not 4): pre-clamp this rawHalfSpan is -1, so this is the case that pins the
+    // clamp itself, not just a halfSpan-already-zero band.
+    const WaveformBand b = waveformBand(10, 3);
     const WaveformColumnSpan s = waveformColumnSpan(b, 1.0, -1.0);
     CHECK(s.top == b.midY && s.bottom == b.midY);
+    // Domain note, not a bug: waveformBand(t, 0) still has lo=t, hi=t-1 (an inverted span) even
+    // though halfSpan clamps to 0 — unreachable via the band allocator (draw_kit.cpp never
+    // divides down to a 0-height band) and harmless if it were (LICE clips a reversed 1px line).
 }
 
 int main() {