fix: close review findings on the velocity-curve deck and bipolar curves

Cancels the curve-node drag whenever the popup closes so Esc mid-drag can't alias the amp curve; generalizes CurveTarget routing to one switch; fixes stale/overstated comments; clamps a pre-v12 depth fold; adds deck-inertness and filter-fold test coverage.

src/core/instrument/map/params_payload.cpp

@@ -140,8 +140,13 @@ void readFilterTail(ByteReader& r, InstrumentParams& p, bool preVelocityVersion)
     f.env.decaySeconds   = bitsToDouble(r.u64());
     f.env.sustainLevel   = bitsToDouble(r.u64());
     f.env.releaseSeconds = bitsToDouble(r.u64());
+    // velAmount feeds a MULTIPLIER on the stored curve's knots (below), not a param the engine
+    // clamps on its own — the UI never dials it outside [-1,1] (deckBipolarFromNorm), so a
+    // corrupt-but-finite blob value outside that range must clamp here rather than silently
+    // scaling the lifted curve past what fromPoints' own [-1,1] box-clamp would then truncate.
     const double velFold =
-        preVelocityVersion ? (std::isfinite(velAmount) ? velAmount : 0.0) : 1.0;
+        preVelocityVersion ? std::clamp(std::isfinite(velAmount) ? velAmount : 0.0, -1.0, 1.0)
+                            : 1.0;
     readCurveTail(r, f.velocityCurve, reasampler::instrument::engine::CurveDomain::Bipolar,
                   velFold);
 }