deck: filter mod moves to FILTER ENV, cell runs centre in their reserves, two-segment toggles become single buttons, deck focuses its overlay

tests/test_deck_values.cpp

@@ -400,8 +400,59 @@ static void testTheFilterFourKeepTheirIdentityTaper() {
     }
 }
 
+// The single-button commit seam. A one-button toggle carries no segment, so the commit derives
+// the NEXT state from the parameter set and hands it to setDeckParam's unchanged segment
+// contract. Driven end-to-end — derive, apply, re-derive — because the property that matters is
+// that repeated clicks alternate the stored field rather than latching it.
+static void testASingleButtonsDerivedSegmentFlipsTheFieldItNames() {
+    PlaySeconds p;
+    // Enables: off by default, so the first derived segment must be ON.
+    CHECK(!p.pitchEnv.enabled);
+    CHECK(nextToggleSegment(DeckParam::kPitchEnvEnable, p) == 1);
+    setDeckParam(DeckParam::kPitchEnvEnable, p, 0.0,
+                 nextToggleSegment(DeckParam::kPitchEnvEnable, p));
+    CHECK(p.pitchEnv.enabled);
+    CHECK(nextToggleSegment(DeckParam::kPitchEnvEnable, p) == 0);
+    setDeckParam(DeckParam::kPitchEnvEnable, p, 0.0,
+                 nextToggleSegment(DeckParam::kPitchEnvEnable, p));
+    CHECK(!p.pitchEnv.enabled);
+
+    CHECK(!p.filter.enabled);
+    CHECK(nextToggleSegment(DeckParam::kFilterEnable, p) == 1);
+    setDeckParam(DeckParam::kFilterEnable, p, 0.0,
+                 nextToggleSegment(DeckParam::kFilterEnable, p));
+    CHECK(p.filter.enabled);
+
+    // Mode selectors: Staged by default, so the first derived segment is Spline. Flipping the
+    // amp to Spline also forces Trigger (the drawn-EG rule), which is setDeckParam's own job
+    // and must survive the derived segment reaching it unchanged.
+    CHECK(p.ampSpline.mode == EnvMode::Staged);
+    CHECK(nextToggleSegment(DeckParam::kAmpEnvMode, p) == 1);
+    setDeckParam(DeckParam::kAmpEnvMode, p, 0.0, nextToggleSegment(DeckParam::kAmpEnvMode, p));
+    CHECK(p.ampSpline.mode == EnvMode::Spline);
+    CHECK(p.playMode == PlayMode::Trigger);
+    CHECK(nextToggleSegment(DeckParam::kAmpEnvMode, p) == 0);
+    setDeckParam(DeckParam::kAmpEnvMode, p, 0.0, nextToggleSegment(DeckParam::kAmpEnvMode, p));
+    CHECK(p.ampSpline.mode == EnvMode::Staged);
+
+    for (DeckParam id : {DeckParam::kPitchEnvMode, DeckParam::kFilterEnvMode}) {
+        setDeckParam(id, p, 0.0, nextToggleSegment(id, p));
+    }
+    CHECK(p.pitchSpline.mode == EnvMode::Spline);
+    CHECK(p.filterSpline.mode == EnvMode::Spline);
+
+    // Every control that still carries its own segment answers "not mine", so the shell can
+    // tell the two commit paths apart on the answer alone.
+    for (DeckParam id : {DeckParam::kPlayMode, DeckParam::kPitchEngine, DeckParam::kFilterLaw,
+                         DeckParam::kVoiceMode, DeckParam::kMonoTrigger,
+                         DeckParam::kFilterCutoff, DeckParam::kCount}) {
+        CHECK(nextToggleSegment(id, p) == -1);
+    }
+}
+
 int main() {
     testTheTwoCeilingNamesAreOneNumber();
+    testASingleButtonsDerivedSegmentFlipsTheFieldItNames();
     testNormRoundTripsThroughEveryValueDomain();
     testRateKnobEndsAreTheStretchersOwnBounds();
     testRateAndPitchBindTheirOwnFields();