fix: close round-3 review findings — smallest-target-first, residue test fix, extraction

Waveform overlay now resolves node/tab/marker click collisions by target area instead of check order; residue test now uses a distinguishing fixture; Gate-unavailable-while-drawn logic extracted to one pure helper shared by resolvePlay and applyControl.

src/core/instrument/engine/play_params.h

@@ -195,6 +195,17 @@ bool splineActive(const Play& p) {
            (p.filter.enabled && p.filterSpline.mode == EnvMode::Spline);
 }
 
+// The one enforcement of the rule above: forces `p` to Trigger the instant it goes
+// splineActive. Every path that can leave `p` in a state splineActive() would newly return true
+// for — resolving stored params toward the engine, or an editor control edit that can flip a
+// mode/enable toggle — routes through this, so none of them can reopen the Gate+spline hole
+// splineActive's own doc comment describes. Header-inline and allocation-free: play_params.h
+// sits on the per-voice-per-sample include path.
+template <class Play>
+void enforceGateUnavailableWhileDrawn(Play& p) {
+    if (splineActive(p)) p.playMode = PlayMode::Trigger;
+}
+
 // [start, end) frames, half-open. A zero-length loop (start == end) is the "no sustain loop"
 // marker — a held note past the sample end goes silent rather than looping a zero span.
 struct SampleLoop {

src/core/instrument/engine/velocity_curve.h

@@ -232,13 +232,14 @@ public:
     // True once the cursor has settled on the contour's LAST segment. On its own this does NOT
     // make a 0 read here a terminus: the final segment's LEFT endpoint can also be 0 (a 2-point
     // contour is nothing but a single "final" segment starting at frame 0), which would read 0
-    // while about to rise. Voice::tickAmplitude pairs this with terminalValue() == 0 — the
+    // while about to rise. Voice::tickAmplitude pairs this with segmentEndValue() == 0 — the
     // segment's RIGHT endpoint, i.e. the whole contour's true end — before calling a 0 read the
     // note's genuine permanent terminus.
     bool onFinalSegment() const { return seg_ + 2 == n_; }
-    // The current segment's right endpoint — the whole contour's terminal Y only when paired
-    // with onFinalSegment() (see there).
-    double terminalValue() const { return y1_; }
+    // The CURRENT SEGMENT's right endpoint — not a contour-level concept despite the name's
+    // shape; it is the whole contour's terminal Y only when paired with onFinalSegment() (see
+    // there). Named for what it returns, not for its one call site's use of it.
+    double segmentEndValue() const { return y1_; }
 
     // `phase` is normalized position over the contour's whole span, [0,1]; out-of-range clamps
     // to the terminal values (a note past its span holds the contour's last level).

src/core/instrument/engine/voice.h

@@ -184,18 +184,11 @@ private:
         // entirely — release() then has no envelope to end, and an active sustain loop rings
         // forever.
         if (ampSplineCur_.active() && playMode_ == PlayMode::Trigger) {
-            // A contour covers the sample end to end, so the head leaving the span IS the end of
-            // the note — the exhaustion path in advanceFrame is what frees the voice. A contour
-            // whose TERMINAL value (the final segment's right endpoint) is 0 reaches a genuine
-            // permanent terminus early, the spline analogue of a staged AHD's finished(). Gating
-            // on the terminal value, not just the segment index, matters because a 2-point
-            // contour IS a single "final" segment from frame 0 — checking onFinalSegment() alone
-            // would call a contour that STARTS at 0 (e.g. a fade-in) over before it ever rises.
-            // Mid-contour dips through 0 still don't free early, since the spline is deliberately
-            // not globally monotone.
+            // Early-free at a genuine permanent terminus (the spline analogue of a staged AHD's
+            // finished()) — onFinalSegment()/segmentEndValue()'s own doc comments own the why.
             amp = ampSplineCur_.eval(splinePhase());
             if (amp == 0.0 && ampSplineCur_.onFinalSegment() &&
-                ampSplineCur_.terminalValue() == 0.0) {
+                ampSplineCur_.segmentEndValue() == 0.0) {
                 amplitudeDone_ = true;
             }
         } else if (playMode_ == PlayMode::Gate) {

src/core/instrument/map/sample_map.cpp

@@ -262,10 +262,10 @@ PlayParams resolvePlay(const PlaySeconds& stored, int sampleRate) {
     out.ampSpline    = stored.ampSpline;
     out.pitchSpline  = stored.pitchSpline;
     out.filterSpline = stored.filterSpline;
-    // Gate is unavailable while any EG is drawn — see splineActive (play_params.h) for why.
-    // The editor refuses the Gate segment for the same reason; enforcing it HERE as well is
-    // what keeps a hand-edited or downgraded blob from reaching the engine as Gate + spline.
-    if (splineActive(stored)) out.playMode = PlayMode::Trigger;
+    // Every field splineActive reads on `out` is already copied from `stored` above, so this
+    // enforces the same rule enforceGateUnavailableWhileDrawn's doc comment (play_params.h)
+    // describes — the editor's applyControl is the other caller, so the two cannot drift.
+    enforceGateUnavailableWhileDrawn(out);
     return out;
 }
 

src/core/instrument/ui/CMakeLists.txt

@@ -24,8 +24,10 @@ reasampler_pure_library(waveform_view
     SOURCES waveform_view.cpp
     LINK PUBLIC editor_geometry peaks PRIVATE sample_bands)
 # sample_bands is linked directly here because the test exercises the lane metrics that
-# waveform_view does not re-export.
-reasampler_test(waveform_view LINK waveform_view sample_bands)
+# waveform_view does not re-export. velocity_curve is linked for the smallest-target-first
+# arbitration tests, which pin the geometric facts editor_input_waveform.cpp's node/tab/marker
+# resolution depends on (the shell itself has no test target).
+reasampler_test(waveform_view LINK waveform_view sample_bands velocity_curve)
 
 reasampler_pure_library(browser_scroll
     SOURCES browser_scroll.cpp

src/shell/instrument/editor_controls.cpp

@@ -274,8 +274,8 @@ void ReaSamplerEditor::applyControl(int id, PlaySeconds& play, double value,
     // (above) or an enable toggle (kPitchEnvEnable/kFilterEnable), whose enabling can make an
     // already-Spline pitch/filter envelope newly active. Applying it once here, rather than at
     // each site that could cause the flip, is what keeps a future such control from reopening
-    // the same hole.
-    if (splineActive(play)) play.playMode = PlayMode::Trigger;
+    // the same hole. `resolvePlay` (sample_map.cpp) is the other caller of the shared helper.
+    enforceGateUnavailableWhileDrawn(play);
 }
 
 double ReaSamplerEditor::liveSampleRate() const {

src/shell/instrument/editor_input_waveform.cpp

@@ -12,7 +12,8 @@
 #include <cstdint>
 #include <vector>
 
-#include "core/instrument/engine/loop/loop_span.h"  // maxCrossfade (the shared drag-clamp bound)
+#include "core/instrument/engine/loop/loop_span.h"     // maxCrossfade (the shared drag-clamp bound)
+#include "core/instrument/engine/velocity_curve.h"      // kCurveNodeGrabRadius (target-size arbitration)
 #include "core/instrument/ui/envelope_edit.h"   // nodeAtPoint / resolveNodeDrag
 #include "core/instrument/ui/spline_edit.h"     // the shared point-editing grammar
 #include "core/instrument/ui/waveform_view.h"   // waveformOverlayArea / markerAtPoint / snap
@@ -24,6 +25,7 @@ namespace reasampler::vst {
 using namespace reasampler::ui;
 using namespace reasampler::instrument::ui;
 using instrument::engine::loop::maxCrossfade;
+using instrument::engine::kCurveNodeGrabRadius;
 
 bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
     const std::vector<AudioSample>& pcm = monoPcmFor(selectedId_);
@@ -59,33 +61,65 @@ bool ReaSamplerEditor::mouseDownWaveform(const FaceLayout& fl, int x, int y) {
             return true;  // node moves once the cursor drags
         }
     }
-    // An existing contour node's grab/toggle/delete runs BEFORE the markers — mirroring
-    // markerHandleRect's tab-vs-column split (below): a coincident pixel (the default contour
-    // endpoint sits at the same x as the default start marker) is resolved by asking the
-    // NARROWER target first. pointAtPixel's pick radius is a small box around the node's own
-    // (x, y), not a full-height column, so this claims only genuine node hits — the marker's
-    // column stays grabbable at every other y along the same x. Never add here (kAdd is only
-    // tried once the markers have also passed on the click, below).
-    if (splineLive && splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/false)) {
-        return true;
+    const SetupMarkers m = pickedMarkers(frames);
+    const std::int64_t markerFrames[3] = {m.start, m.loopStart, m.loopEnd};
+
+    // Three affordances can claim the same pixel: a contour node (a small fixed pick box), the
+    // crossfade tab (a small clipped top-strip tab), and a marker's full-height grab column
+    // (waveform_view.h's tab-vs-column split already keeps the tab apart from ITS OWN column;
+    // this is the cross-affordance case on top of that). Resolving by any fixed check order
+    // shadows whichever one loses the tie — this seam regressed twice from exactly that fix.
+    // Instead measure each claimant's own target area and let the SMALLEST hit win: the marker
+    // column is the odd one out (its target is the whole band height), so it only wins where
+    // nothing narrower also claims the pixel. Never add here (kAdd is only tried once nothing
+    // else has claimed the click, below).
+    struct Candidate {
+        bool hit = false;
+        std::int64_t area = 0;
+    };
+
+    Candidate node;
+    if (splineLive) {
+        const VelocityCurve::Box box = splineOverlayBox(overlay);
+        // Also require strict in-box, matching splineOverlayClick's own narrowing (spline_edit.h's
+        // grammar note) — otherwise this candidate could "win" the arbitration below for a click
+        // splineOverlayClick would then refuse, silently swallowing it instead of falling through
+        // to the tab/marker checks.
+        if (contains(overlay.rect, x, y) && splineFor(overlayEnv_).pointAtPixel(box, x, y) >= 0) {
+            node.hit = true;
+            constexpr std::int64_t side = 2 * kCurveNodeGrabRadius + 1;
+            node.area = side * side;
+        }
     }
 
-    const SetupMarkers m = pickedMarkers(frames);
-    // The crossfade handle first, and only when there IS a loop to fade: at a zero fade it
-    // sits exactly on the loop start, so it can only stay reachable by owning the top strip
-    // (waveform_view.h's handle-vs-column split) and being asked first. The same ambiguity
-    // recurs whenever ANY marker's frame lands on loopStart - crossfade (most plausibly the
-    // start marker dragged up against the fade edge), so this check has to run before the
-    // marker array below regardless of which marker the collision is with.
-    if (m.hasLoop &&
-        contains(markerHandleRect(overlay, frames, m.loopStart - m.crossfade), x, y)) {
+    Candidate tab;
+    const Rect tabRect =
+        m.hasLoop ? markerHandleRect(overlay, frames, m.loopStart - m.crossfade) : Rect{};
+    if (m.hasLoop && contains(tabRect, x, y)) {
+        tab.hit = true;
+        tab.area = static_cast<std::int64_t>(tabRect.width) * tabRect.height;
+    }
+
+    const int markerHit = markerAtPoint(overlay, frames, markerFrames, 3, x, y);
+    Candidate marker;
+    if (markerHit >= 0) {
+        marker.hit = true;
+        marker.area = static_cast<std::int64_t>(2 * kMarkerGrabWidth + 1) * overlay.rect.height;
+    }
+
+    // Node checked before marker on an area tie so a degenerate (zero-height) overlay still
+    // prefers the node — unreachable in practice (sample_bands floors the band well above it),
+    // kept only so this arbitration has one well-defined answer for every input, not just the
+    // ones the current geometry constants happen to produce.
+    if (node.hit && (!tab.hit || node.area <= tab.area) && (!marker.hit || node.area <= marker.area)) {
+        return splineOverlayClick(overlay, x, y, gesture, /*addOnEmptySpace=*/false);
+    }
+    if (tab.hit && (!marker.hit || tab.area <= marker.area)) {
         beginMarkerDrag(WaveMarker::kLoopXfade, m, frames, x);
         return true;
     }
-    const std::int64_t markerFrames[3] = {m.start, m.loopStart, m.loopEnd};
-    const int hit = markerAtPoint(overlay, frames, markerFrames, 3, x, y);
-    if (hit >= 0) {
-        beginMarkerDrag(static_cast<WaveMarker>(hit), m, frames, x);
+    if (marker.hit) {
+        beginMarkerDrag(static_cast<WaveMarker>(markerHit), m, frames, x);
         return true;
     }
     // Nothing else wanted the click: now the drawn contour may take the empty space.
@@ -98,10 +132,7 @@ bool ReaSamplerEditor::splineOverlayClick(const OverlayArea& waveArea, int x, in
     const VelocityCurve::Box box = splineOverlayBox(waveArea);
     VelocityCurve& contour = splineFor(overlayEnv_);
     SplineEdit edit = resolveSplineEdit(contour, box, gesture, x, y);
-    // resolveSplineEdit's outside-box grab/delete/toggle allowance (pointAtPixel's radius has
-    // no box check of its own) was designed for the popup's inset ring; the overlay box has NO
-    // inset (splineOverlayBox), so honoring it here would extend the grab halo 6px into the
-    // inter-band pad. kAdd already requires in-box (resolveSplineEdit's own check).
+    // The overlay's outside-box narrowing — see spline_edit.h's grammar note for why.
     if (edit.kind != SplineEditKind::kNone && edit.kind != SplineEditKind::kAdd &&
         !(x >= box.left && x < box.left + box.width && y >= box.top && y < box.top + box.height)) {
         edit = SplineEdit{};

tests/test_deck_groups.cpp

@@ -565,30 +565,8 @@ static void testNoFaceLeavesSlackWhereItsDroppedControlsWere() {
     }
 }
 
-// Every shipped face's reserve divides its present-cell count evenly (see
-// testNoFaceLeavesSlackWhereItsDroppedControlsWere), so none of them exercises the
-// "residue lands in symmetric end margins" rule knob_deck.cpp documents — only that the
-// leftover is small, not where it goes. A synthetic 7-slot reserve with 5 present (336/5,
-// remainder 1) forces a real residue and pins it split across BOTH ends.
-static void testASyntheticIndivisibleReserveSplitsItsResidueAcrossBothEnds() {
-    const DeckGroupDesc g{0, 78, {}, {100, 44}, {}, {20, 21, 22, 23, 24, -1, -1}, {}};
-    const std::vector<DeckGroupDesc> gs{g};
-    const DeckLayout dl = layoutDeck(gs, 0, 0, kAvailAtMinWidth);
-    const DeckGroupLayout& lay = dl.groups[0];
-    CHECK(lay.cells.size() == 5);
-
-    const int run = 7 * kDeckCellW;
-    const int cellW = run / 5;                // the same integer division layoutGroup uses
-    const int residue = run - cellW * 5;       // 1: nonzero, unlike every shipped face's reserve
-    CHECK(residue > 0);
-
-    const int covered = lay.cells.back().cell.right() - lay.cells.front().cell.x;
-    CHECK(run - covered == residue);
-    const int leadPad = lay.cells.front().cell.x - (lay.box.x + kDeckGroupPadX);
-    const int trailPad = (lay.box.right() - kDeckGroupPadX) - lay.cells.back().cell.right();
-    CHECK(leadPad == residue / 2);
-    CHECK(trailPad == residue - leadPad);      // both ends share it, not one cell absorbing it
-}
+// The "residue lands in symmetric end margins" rule is knob_deck's own (layoutGroup), pinned
+// once by its synthetic residue>=2 fixture in test_knob_deck.cpp rather than restated here.
 
 // Gate is the common face and it already packs correctly: pin its group widths and row
 // assignment at the floor so a later edit anywhere in the deck cannot reflow it silently.
@@ -691,7 +669,6 @@ int main() {
     testWrappedDeckHeightAtTheEditorFloorWidth();
     testDeckFitsInsideTheEnforcedMinimumWindow();
     testNoFaceLeavesSlackWhereItsDroppedControlsWere();
-    testASyntheticIndivisibleReserveSplitsItsResidueAcrossBothEnds();
     testGateModeWidthsAndRowAssignmentAreUnchanged();
     testGateSplineGateRoundTripsToTheSameLayout();
     testHitTestResolvesTheNewFilterControls();

tests/test_knob_deck.cpp

@@ -148,8 +148,11 @@ static void testHitTest() {
     h = hitTestDeck(dl, voice.rowToggle.seg1.x + 1, voice.rowToggle.seg1.y + 1);
     CHECK(h.kind == DeckHitKind::RowToggle && h.id == 104 && h.segment == 1);
 
-    // A reserve (id -1) yields no cell of its own, so every point of the knob row lands on a
-    // real control: no dead rect survives for a grab to fall into.
+    // A reserve (id -1) yields no cell of its own. This fixture's reserve divides its present
+    // cells evenly (5 slots / 3 present -> 240/3, no residue), so every point of the knob row
+    // lands on a real control: no dead rect survives for a grab to fall into. That does NOT
+    // generalize to an indivisible reserve — a residue leaves a few uncovered margin pixels by
+    // design (testIndivisibleResidueSplitsSymmetricallyAcrossBothEnds, below).
     std::vector<DeckGroupDesc> trig;
     trig.push_back({0, 78, {}, {100, 44}, {}, {20, 21, 22, -1, -1}, {}});
     const DeckLayout tl = layoutDeck(trig, 0, 0, 824);
@@ -220,26 +223,32 @@ static void testReservedCellWidthGoesToTheCellsPresent() {
 }
 
 // The three faces above (240/3, 240/4, 240/1) all divide their run evenly, so none of them
-// actually exercises "residue in symmetric end margins" — a 7-slot reserve with 5 present
-// (336/5, remainder 1) does, and pins the residue split across BOTH ends rather than only
-// the leading one.
-static void testIndivisibleResidueLandsInSymmetricEndMargins() {
-    const DeckGroupDesc g{0, 78, {}, {100, 44}, {}, {20, 21, 22, 23, 24, -1, -1}, {}};
+// actually exercises "residue in symmetric end margins". An 8-slot reserve with 5 present
+// (384/5 = 76 r4) does: residue 4 is the smallest case that can tell a symmetric split (2/2)
+// apart from a trailing-only one (0/4) — a residue of 1 (0/1 vs 1/0... i.e. 0/1) can't, since
+// leadPad = residue/2 rounds to 0 either way, which is exactly why this seam's earlier test
+// passed without pinning the rule it was named for.
+static void testIndivisibleResidueSplitsSymmetricallyAcrossBothEnds() {
+    const DeckGroupDesc g{0, 78, {}, {100, 44}, {}, {20, 21, 22, 23, 24, -1, -1, -1}, {}};
     std::vector<DeckGroupDesc> gs{g};
     const DeckLayout dl = layoutDeck(gs, 0, 0, 824);
     const DeckGroupLayout& lay = dl.groups[0];
     CHECK(lay.cells.size() == 5);
 
-    const int run = 7 * kDeckCellW;
+    const int run = 8 * kDeckCellW;
     const int present = 5;
-    const int cellW = run / present;               // 67: the same integer division the layout uses
-    const int expectedResidue = run - cellW * present;  // 1: the case the even-dividing faces can't reach
-    CHECK(expectedResidue > 0);
+    const int cellW = run / present;               // 76: the same integer division the layout uses
+    const int expectedResidue = run - cellW * present;  // 4
+    CHECK(expectedResidue == 4);
 
     const int covered = lay.cells.back().cell.right() - lay.cells.front().cell.x;
     CHECK(run - covered == expectedResidue);
     const int leadPad = lay.cells.front().cell.x - (lay.box.x + kDeckGroupPadX);
     const int trailPad = (lay.box.right() - kDeckGroupPadX) - lay.cells.back().cell.right();
+    // Hard literals, not just the formula: this is the case that actually distinguishes
+    // symmetric (2/2) from trailing-only (0/4) — see the comment above.
+    CHECK(leadPad == 2);
+    CHECK(trailPad == 2);
     CHECK(leadPad == expectedResidue / 2);
     CHECK(trailPad == expectedResidue - leadPad);  // both ends share it, not one absorbing it
 }
@@ -337,7 +346,7 @@ int main() {
     testGroupInnerGeometry();
     testHitTest();
     testReservedCellWidthGoesToTheCellsPresent();
-    testIndivisibleResidueLandsInSymmetricEndMargins();
+    testIndivisibleResidueSplitsSymmetricallyAcrossBothEnds();
     testCaptionRadioGeometryAndHit();
     testInnerDialHit();
     testCaptionToggle2();

tests/test_spline_egs.cpp

@@ -344,6 +344,25 @@ static void testTwoPointContourRisingFromZeroSoundsForItsFullSpan() {
     CHECK(v.soundingNote());              // still sounding at the midpoint, rising toward 1
 }
 
+// The positive direction of the fix above: a contour whose final segment is flat at 0 (here,
+// the whole two-point span) DOES free the voice early, on its very first tick. Nothing exercises
+// this without it — a future tightening of the gate (e.g. requiring more than onFinalSegment() +
+// segmentEndValue()) could silently turn the early-free off, which is a performance regression
+// (a ringing but silent voice) rather than an audible one, so nothing else would catch it.
+static void testFlatZeroFinalSegmentStillFreesTheVoiceEarly() {
+    const VelocityCurve contour =
+        VelocityCurve::fromPoints({{kVelMin, 0.0}, {kVelMax, 0.0}}, CurveDomain::Unipolar);
+    const std::size_t frames = 1000;
+    const SampleData s = splineAmpSample(frames, contour);
+
+    Voice v;
+    v.start(60, 100, s);
+    CHECK(v.soundingNote());              // fresh note: sounding before anything is rendered
+    const double y0 = v.renderFrame();
+    CHECK(near(y0, 0.0, 1e-9));
+    CHECK(!v.soundingNote());             // a genuine permanent terminus, not a mid-contour dip
+}
+
 // --- 9. A fresh spline EG opens on the smooth y = 1 - x ----------------------
 
 static void testAFreshSplineEgDefaultsToTheSmoothDownwardSlope() {
@@ -424,6 +443,27 @@ static void testGateIsUnavailableWhileASplineEgIsActiveAndReturnsAfterwards() {
     CHECK(!deckKnobInert(DeckParam::kFilterModAmt, gates));
 }
 
+// enforceGateUnavailableWhileDrawn (play_params.h) is the ONE enforcement resolvePlay and the
+// editor's applyControl both call — resolvePlay's own coverage above only exercises it through
+// the frames mirror; pin it directly over BOTH representations it is shared between, closing the
+// coverage gap the extraction was for (applyControl has no shell test target of its own).
+static void testEnforceGateUnavailableWhileDrawnForcesTriggerOnBothRepresentations() {
+    PlaySeconds seconds;
+    seconds.playMode = PlayMode::Gate;
+    enforceGateUnavailableWhileDrawn(seconds);
+    CHECK(seconds.playMode == PlayMode::Gate);  // not splineActive -> untouched
+    seconds.ampSpline.mode = EnvMode::Spline;
+    enforceGateUnavailableWhileDrawn(seconds);
+    CHECK(seconds.playMode == PlayMode::Trigger);
+
+    PlayParams frames;
+    frames.playMode = PlayMode::Gate;
+    frames.filter.enabled = true;
+    frames.filterSpline.mode = EnvMode::Spline;
+    enforceGateUnavailableWhileDrawn(frames);
+    CHECK(frames.playMode == PlayMode::Trigger);
+}
+
 // --- 11. The velocity->amp curve is the same grammar -------------------------
 
 static void testTheVelocityAmpCurveGainsTheToggleAndKeepsItsDelete() {
@@ -491,8 +531,10 @@ int main() {
     testAV12PayloadLoadsWithoutLoss();
     testAContourReplaysProportionallyOnADifferentLengthSample();
     testTwoPointContourRisingFromZeroSoundsForItsFullSpan();
+    testFlatZeroFinalSegmentStillFreesTheVoiceEarly();
     testAFreshSplineEgDefaultsToTheSmoothDownwardSlope();
     testGateIsUnavailableWhileASplineEgIsActiveAndReturnsAfterwards();
+    testEnforceGateUnavailableWhileDrawnForcesTriggerOnBothRepresentations();
     testTheVelocityAmpCurveGainsTheToggleAndKeepsItsDelete();
     testSplineCursorBinarySearchAgreesWithTheColdReaderOnAJumpingRead();
     if (g_fail == 0) std::printf("spline_egs: all tests passed\n");

tests/test_waveform_view.cpp

@@ -13,6 +13,7 @@
 // stacked height, grabs reaching the lower lane); laneEnvelope (per-lane channel split).
 
 #include "../src/core/instrument/ui/waveform_view.h"
+#include "../src/core/instrument/engine/velocity_curve.h"  // kCurveNodeGrabRadius, VelocityCurve::pointAtPixel
 #include "../src/core/instrument/ui/sample_bands.h"  // kWaveformMinHeight, kLaneGap
 
 #include <cstddef>
@@ -21,6 +22,7 @@
 
 using namespace reasampler;
 using namespace reasampler::instrument::ui;
+using namespace reasampler::instrument::engine;
 using reasampler::audio::AudioSample;
 
 static int g_fail = 0;
@@ -379,10 +381,107 @@ static void testStartMarkerSharesTheHandleStripWhenItSitsAtTheFadeEdge() {
     // column to the start marker (index 0) at this x/y...
     CHECK(markerAtPoint(overlayOf(a), 1000, markers, 3, mx, topY) == 0);
     // ...and the fade handle's rect claims the exact same pixel — the ambiguity the shell
-    // resolves by asking the handle first, same as it does for the zero-fade/loop-start case.
+    // resolves by smallest-target-first (the handle's clipped tab is always the narrower
+    // target), same as it does for the zero-fade/loop-start case.
     CHECK(contains(markerHandleRect(overlayOf(a), 1000, fadeEdge), mx, topY));
 }
 
+// --- Smallest-target-first: the three-way coincidence with a spline contour node -------
+//
+// editor_input_waveform.cpp's mouseDownWaveform resolves a click among a contour node (a fixed
+// pick box), the crossfade tab, and a marker's full-height column by measuring each candidate's
+// own target area and letting the smallest win — this module can't exercise the shell's
+// arbitration itself (no shell test target wraps the editor), but it can pin the geometric facts
+// that arbitration depends on, over the pure primitives it composes. A realistic band height
+// (kWaveformMinHeight, the product's own floor) is used throughout so these numbers are the
+// worst case for the node, not a favourable one.
+static VelocityCurve::Box boxOf(const Rect& r) { return VelocityCurve::Box{r.x, r.y, r.width, r.height}; }
+
+// Case (a): a fresh Spline default (rampDown) puts its endpoint 0 at (box.left, box.top) — the
+// exact pixel the start marker draws at frame 0. The node's fixed 169px pick box is far smaller
+// than a kWaveformMinHeight-tall marker column, so the endpoint stays reachable.
+static void testFreshRampDownEndpointBeatsTheStartMarkerAtFrameZero() {
+    const Rect a = Rect{20, 10, 1000, kWaveformMinHeight};
+    const OverlayArea overlay = overlayOf(a);
+    const std::int64_t frames = 100000;
+    const VelocityCurve contour = VelocityCurve::rampDown();
+    const VelocityCurve::Box box = boxOf(a);
+
+    CHECK(contour.pointAtPixel(box, a.x, a.y) == 0);  // endpoint 0 sits at (box.left, box.top)
+    const std::int64_t markers[1] = {0};
+    CHECK(markerAtPoint(overlay, frames, markers, 1, a.x, a.y) == 0);  // the coincidence
+
+    constexpr std::int64_t nodeSide = 2 * kCurveNodeGrabRadius + 1;
+    constexpr std::int64_t nodeArea = nodeSide * nodeSide;  // 169, fixed
+    const std::int64_t markerArea =
+        static_cast<std::int64_t>(2 * kMarkerGrabWidth + 1) * a.height;  // 11 * band height
+    CHECK(nodeArea < markerArea);  // the node wins: the endpoint stays a genuine grab target
+}
+
+// Case (b): the crossfade tab at zero crossfade sits on loopStart's own pixel column; a node
+// dragged to value ~0.98 lands a couple of rows below the box top — inside the tab's own
+// top-strip band, where the review found the tab fully shadowed by a node-first pass.
+static void testCrossfadeTabBeatsAContourNodeNearItsTopStrip() {
+    const Rect a = Rect{20, 10, 1000, kWaveformMinHeight};
+    const OverlayArea overlay = overlayOf(a);
+    const std::int64_t frames = 100000;
+    const std::int64_t loopStart = 40000, crossfade = 0;  // zero crossfade -> tab sits on loopStart
+    const int mx = frameToX(overlay, frames, loopStart - crossfade);
+    const Rect tabRect = markerHandleRect(overlay, frames, loopStart - crossfade);
+    CHECK(!tabRect.empty());
+
+    const VelocityCurve::Box box = boxOf(a);
+    const int ny = a.y + 3;  // ~0.98 up a kWaveformMinHeight-tall box; inside the tab's top strip
+    VelocityCurve c = VelocityCurve::flat();
+    const VelocityPoint p = c.pointFromPixel(box, mx, ny);
+    c.addPoint(p.velocity, p.value);
+    CHECK(c.pointAtPixel(box, mx, ny) >= 0);
+    CHECK(contains(tabRect, mx, ny));  // the coincidence: both claim the same pixel
+
+    constexpr std::int64_t nodeSide = 2 * kCurveNodeGrabRadius + 1;
+    constexpr std::int64_t nodeArea = nodeSide * nodeSide;                  // 169, fixed
+    const std::int64_t tabArea = static_cast<std::int64_t>(tabRect.width) * tabRect.height;  // <= 110
+    CHECK(tabArea < nodeArea);  // the tab wins: it stays the only affordance at zero crossfade
+
+    // The residual the review names: the node keeps its OUTER columns, one pixel past the tab's
+    // clipped edge but still inside its own pick radius.
+    const int outerX = mx + kMarkerHandleHalfWidth + 1;
+    CHECK(!contains(tabRect, outerX, ny));
+    CHECK(c.pointAtPixel(box, outerX, ny) >= 0);
+}
+
+// Case (c): a contour node coincident with a loop marker. At kWaveformMinHeight (the product's
+// own floor) the column is already an order of magnitude larger than the node's fixed pick box,
+// so the node wins the shared pixel while the column stays reachable everywhere the node isn't.
+static void testContourNodeBeatsALoopMarkerAtTheirSharedPixelButNotElsewhere() {
+    const Rect a = Rect{20, 10, 1000, kWaveformMinHeight};
+    const OverlayArea overlay = overlayOf(a);
+    const std::int64_t frames = 100000;
+    const std::int64_t loopEnd = 70000;
+    const int mx = frameToX(overlay, frames, loopEnd);
+    const std::int64_t markers[1] = {loopEnd};
+
+    const VelocityCurve::Box box = boxOf(a);
+    const int ny = a.y + a.height / 2;  // mid-height, well clear of any tab
+    VelocityCurve c = VelocityCurve::flat();
+    const VelocityPoint p = c.pointFromPixel(box, mx, ny);
+    c.addPoint(p.velocity, p.value);
+    CHECK(c.pointAtPixel(box, mx, ny) >= 0);
+    CHECK(markerAtPoint(overlay, frames, markers, 1, mx, ny) == 0);  // the coincidence
+
+    constexpr std::int64_t nodeSide = 2 * kCurveNodeGrabRadius + 1;
+    constexpr std::int64_t nodeArea = nodeSide * nodeSide;  // 169, fixed
+    const std::int64_t markerArea =
+        static_cast<std::int64_t>(2 * kMarkerGrabWidth + 1) * a.height;  // 11 * band height
+    CHECK(nodeArea < markerArea);  // the node wins the shared pixel
+
+    // A few rows clear of the node (outside its 13px pick box, still on the marker's column)
+    // the marker alone claims the click.
+    const int farY = ny + kCurveNodeGrabRadius + 4;
+    CHECK(c.pointAtPixel(box, mx, farY) < 0);
+    CHECK(markerAtPoint(overlay, frames, markers, 1, mx, farY) == 0);
+}
+
 // --- Per-lane envelope content -------------------------------------------------
 
 static void testAsymmetricStereoLanesCarryDifferentContent() {
@@ -458,6 +557,9 @@ int main() {
     testMarkerHandleClipsIntoTheArea();
     testMarkerHandleOnDegenerateAreas();
     testStartMarkerSharesTheHandleStripWhenItSitsAtTheFadeEdge();
+    testFreshRampDownEndpointBeatsTheStartMarkerAtFrameZero();
+    testCrossfadeTabBeatsAContourNodeNearItsTopStrip();
+    testContourNodeBeatsALoopMarkerAtTheirSharedPixelButNotElsewhere();
 
     testAsymmetricStereoLanesCarryDifferentContent();
     testLaneEnvelopeRejectsOutOfRangeLane();