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