instrument: deliver continuous playback params live to sounding voices via a seqlock block, holding normalized stage position across time edits

src/core/instrument/engine/live_params.cpp

@@ -0,0 +1,26 @@
+// live_params.cpp — the fold from the parameter set to the live block, and the ramp-step law.
+// See live_params.h for the publication contract.
+
+#include "core/instrument/engine/live_params.h"
+
+namespace reasampler::instrument::engine {
+
+LiveValues foldLive(const PlayParams& params) {
+    LiveValues v;
+    v.filterSettings = params.filter.settings;
+    v.filterModAmount = params.filter.modAmount;
+    v.filterKeyTrack = params.filter.keyTrack;
+    v.filterEnv = params.filter.env;
+    v.adsr = params.adsr;
+    v.pitchEnvAttackFrames = params.pitchEnv.attackFrames;
+    v.pitchEnvDecayFrames = params.pitchEnv.decayFrames;
+    v.pitchEnvPeakSemitones = params.pitchEnv.peakSemitones;
+    return v;
+}
+
+double liveRampStep(double sampleRate) {
+    if (!(sampleRate > 0.0)) return 0.0;  // also catches NaN
+    return 1.0 / (kLiveRampSeconds * sampleRate);
+}
+
+}  // namespace reasampler::instrument::engine