Service both VST3 parameter channels, and promote pitch key-track and Trigger length so all 44 ids issue

The SDK's own single-component sample drains inputParameterChanges in
process() and implements setParamNormalized; automation was reading the
GUI channel alone. The audio thread now patches a block it solely owns.

src/core/instrument/engine/filter/CMakeLists.txt

@@ -1,10 +1,16 @@
 # Control mapping, SVF coefficients, morph weights, and the filter type each get their own
 # TU; VoiceFilter::process stays header-inline so the kernel still inlines at the call site.
+# The frozen control-position laws are their own target: they are the filter's PARAMETER
+# surface, and the VST3 parameter layer reports Hz/Q/drive through them. Kept separable so
+# that consumer does not take a link edge onto the per-voice kernel — the extension's link
+# graph must never be able to reach the voice DSP (root CLAUDE.md, the bake invariant).
+reasampler_pure_library(filter_params SOURCES filter_params.cpp)
+
 reasampler_pure_library(filter SOURCES
-    filter_params.cpp
     filter_coeffs.cpp
     filter_morph.cpp
-    voice_filter.cpp)
+    voice_filter.cpp
+    LINK PUBLIC filter_params)
 
 # Four test targets along the module's own seams so each asserts one domain. filter_tests
 # alone owns the analytic reference and the steady-state gain measurement — a forked copy of

src/core/instrument/engine/live_params.cpp

@@ -5,8 +5,13 @@
 
 namespace reasampler::instrument::engine {
 
-LiveValues foldLive(const PlayParams& params) {
+LiveValues foldLive(const PlayParams& params, double keyTrack) {
     LiveValues v;
+    v.keyTrack = keyTrack;
+    // Folded here, not at the voice: Voice::start reads the block's value directly, so the
+    // spline rule has to be applied on the way in or the two would answer differently.
+    v.splineActive = splineActive(params);
+    v.lengthFraction = effectiveLengthFraction(params);
     v.filterSettings = params.filter.settings;
     v.filterModAmount = params.filter.modAmount;
     v.filterVelAmount = params.filter.velAmount;

src/core/instrument/engine/live_params.h

@@ -52,6 +52,19 @@ struct LiveValues {
     // ordinarily live.
     double       playRate = 1.0;
     double       pitchOffsetSemitones = 0.0;
+    // Two more members of playRate's note-on-latched class, here for the same reason it is:
+    // both resolve a fact the voice fixes at note-on (the pitch ratio, and playEnd_), so live
+    // delivery would retune or re-span a note already struck. Voice::start receives them as
+    // arguments; applyLive never touches either.
+    double       keyTrack = kKeyTrackDefault;
+    // ALREADY spline-folded (effectiveLengthFraction) — a drawn contour is a pure time function
+    // over the whole sample, so the stored knob is inert while one is active and the block must
+    // carry what the voice will actually play, not the stored value.
+    double       lengthFraction = 1.0;
+    // The drawn-EG state the fold above reads. A mode flip travels by reload like the contours
+    // themselves, so this is not a control; it rides here only so a block-boundary write of
+    // Trigger length (a host automation point) can apply the SAME fold rather than un-doing it.
+    bool         splineActive = false;
 };
 
 // The seqlock copies the block as raw bytes, which is only defensible for a plain value type.
@@ -59,8 +72,10 @@ static_assert(std::is_trivially_copyable_v<LiveValues>,
               "the live block is copied under a seqlock — it must stay a plain value");
 
 // The ONE derivation of the live block from the parameter set. Every publisher goes through
-// here so there is a single site to keep in step with PlayParams.
-LiveValues foldLive(const PlayParams& params);
+// here so there is a single site to keep in step with PlayParams. `keyTrack` is passed in
+// because it belongs to the capture/instrument scalar beside the play bundle, not to
+// PlayParams — SampleData::keyTrack at the reload, InstrumentParams::keyTrack at a live commit.
+LiveValues foldLive(const PlayParams& params, double keyTrack);
 
 // Single-writer / single-reader seqlock. The writer publishes a whole block between an odd
 // and an even generation; the reader copies the block and re-checks the generation, retrying
@@ -96,6 +111,10 @@ public:
         seq_.store(next, std::memory_order_release);      // even: complete and coherent
     }
 
+    // The last generation published, without copying the block — one relaxed load, so a reader
+    // that only needs "has anything moved" pays nothing for asking on a block where nothing has.
+    std::uint32_t generation() const { return seq_.load(std::memory_order_relaxed); }
+
     // Copies the block into `out` and returns the generation actually observed, or 0 when
     // nothing has been published yet or the retry budget ran out (in which case `out` may hold
     // a torn copy and MUST be discarded — compare the return against 0 before using it).

src/core/instrument/engine/master_gain.cpp

@@ -17,6 +17,13 @@ double masterGainMaxLinear() { return std::pow(10.0, kMasterGainMaxDb / 20.0); }
 double masterGainDbFromNorm(double norm) {
     norm = clamp01(norm);
     if (norm <= 0.0) return -std::numeric_limits<double>::infinity();
+    // UNITY IS EXACT, and the argument is arithmetic rather than structural — a host's
+    // reset-to-default arrives here as toPlain(defaultNormalized) and must land on 0.0 dB, not a
+    // hair off it. fl(60/84) differs from 60/84 by δ ≈ 1.6e-17; 84·δ ≈ 1.33e-15 sits under the
+    // half-ulp of 60 (3.55e-15), so -60 + fl(60/84)·84 rounds to exactly 60 and the sum to 0.
+    // PRECONDITION: no FP contraction. Fused into a single FMA the residue survives as 1.33e-15.
+    // Safe on the shipped MSVC/x64 default (no FMA without /arch:AVX2); a build that enables
+    // contraction here breaks the exactness test in test_param_units, which is where it surfaces.
     return kMasterGainMinDb + norm * (kMasterGainMaxDb - kMasterGainMinDb);
 }
 

src/core/instrument/engine/play_params.h

@@ -148,6 +148,11 @@ struct FilterParams {
 // with the pitch envelope's own depth throw so the two pitch modulators speak one range.
 inline constexpr double kVelocityPitchRangeSemitones = 24.0;
 
+// Standard 12-tone-ET tracking, and the ONE home for that number: the capture's own scalar, the
+// instrument's stored scalar and the live block all default from here, so a blob predating the
+// field and a block published before the first note can never disagree about it.
+inline constexpr double kKeyTrackDefault = 1.0;
+
 // Bundle a voice reads at start(). Defaults reproduce the bare engine (Gate, hold-0 AHDSR,
 // Varispeed, pitch envelope off, filter off, no velocity->pitch) — core regression tests rely
 // on this; the Preserve product default is layered on at (de)serialization, see
@@ -267,7 +272,7 @@ struct SampleData {
     // How far keyboard pitch tracks the root: 1.0 = standard 12-tone-ET (default); 0.0 = no
     // tracking (every key plays root pitch); 2.0 = double-rate. Scales the (note-root) semitone
     // offset in keyTrackedRatio; rides both repitch engines via the voice's baseRatio_.
-    double keyTrack = 1.0;
+    double keyTrack = kKeyTrackDefault;
 
     // Maps note-on velocity (0..127) to the voice's amp gain, eval'd once in Voice::start
     // (never per frame). Default flat y=1 — every velocity plays at unity.

src/core/instrument/engine/voice.cpp

@@ -19,7 +19,7 @@ void Voice::presizePreserveShifters(std::int64_t windowFrames) {
 }
 
 void Voice::start(int note, int velocity, const SampleData& sample, bool declickTakeover,
-                  double stretchRate) {
+                  double stretchRate, double keyTrack, double lengthFraction) {
     // Before any state reset, record the pre-cut reference (last rendered output) and mark
     // the compensation pending iff this start is a takeover/steal of a sounding voice and the
     // caller opted in. The ramp is seeded on the first frame rendered after the restart, from
@@ -72,6 +72,7 @@ void Voice::start(int note, int velocity, const SampleData& sample, bool declick
     // the control outright — the predicate is spelled the same way advanceFrame spells it.
     preserveRead_ = (pitchEngine_ == PitchEngine::Preserve) && shiftL_.configured();
     rateRatio_ = preserveRead_ ? 1.0 : stretchRate_;
+    keyTrack_ = (keyTrack < 0.0) ? sample.keyTrack : keyTrack;
     recomputeBaseRatio();
     // pitchOffsetRatio_ is a power of 2 and never zero, so this inverse is well-defined — and at
     // Pitch 0 it is a division by exactly 1.0.
@@ -120,10 +121,9 @@ void Voice::start(int note, int velocity, const SampleData& sample, bool declick
     } else {
         // Trigger: play [start, playEnd) where playEnd = start + round(frac*(frames-start)) —
         // map/trigger_seam.h's formula, evaluated inline because the engine does not depend on
-        // map/. The spline fold is effectiveLengthFraction (play_params.h); a second copy of it
-        // here is what let a stored-but-inert %-knob shorten the bake while the voice played
-        // the whole take.
-        double frac = effectiveLengthFraction(p);
+        // map/. The caller's value is ALREADY spline-folded (foldLive does it); the snapshot
+        // fallback folds here, because a stored-but-inert %-knob must not shorten the span.
+        double frac = (lengthFraction < 0.0) ? effectiveLengthFraction(p) : lengthFraction;
         if (!(frac > 0.0)) frac = 0.0;    // %=0 (or a corrupt NaN) -> finishes immediately
         if (frac > 1.0) frac = 1.0;
         std::int64_t playLen = static_cast<std::int64_t>(

src/core/instrument/engine/voice.h

@@ -45,6 +45,9 @@ inline double pitchRatio(int note, int rootNote) {
 // ((note-root)*1.0 is exact in IEEE-754 for an integer-valued double, feeding the same
 // std::pow call); 0.0 means every key plays the root pitch; 2.0 doubles the tracking rate.
 // At the root note the offset is 0 regardless of keyTrack.
+// "Not supplied" for Voice::start's two snapshot-defaulted note-on latches; see start().
+inline constexpr double kLatchFromSnapshot = -1.0;
+
 inline double keyTrackedRatio(int note, int rootNote, double keyTrack) {
     const double semis = static_cast<double>(note - rootNote) * keyTrack;
     return std::pow(2.0, semis / 12.0);
@@ -124,8 +127,16 @@ public:
     // to consult gets exactly that; VoiceEngine::startVoice is what resolves the real value —
     // sample.play.playRate is NOT read here, because the published block outranks the snapshot's
     // possibly-stale copy of it.
+    //
+    // `keyTrack` and `lengthFraction` are the other two members of stretchRate's note-on-latched
+    // class and arrive the same way, for the same structural reason. Negative = not supplied,
+    // which reads the snapshot's own value (sample.keyTrack, effectiveLengthFraction(play)) —
+    // both are non-negative by domain, so the sentinel can never collide with a real one.
+    // VoiceEngine::startVoice always supplies them, resolved from the published block when there
+    // is one; the sentinel is for a caller that has no block to consult.
     void start(int note, int velocity, const SampleData& sample, bool declickTakeover = false,
-               double stretchRate = 1.0);
+               double stretchRate = 1.0, double keyTrack = kLatchFromSnapshot,
+               double lengthFraction = kLatchFromSnapshot);
 
     // Mono legato takeover: re-pitch this active voice to `note` without touching the
     // amplitude envelope, read position, or shifter state — pitch moves, no re-attack. Both
@@ -201,7 +212,7 @@ private:
     // shifter's transpose. Cold: note-on, legato retune, and a live block, never per frame.
     void recomputeBaseRatio() {
         if (sample_ == nullptr) return;
-        baseRatio_ = keyTrackedRatio(note_, sample_->rootNote, sample_->keyTrack) *
+        baseRatio_ = keyTrackedRatio(note_, sample_->rootNote, keyTrack_) *
                      velPitchRatio_ * pitchOffsetRatio_ * rateRatio_;
     }
 
@@ -710,6 +721,10 @@ private:
     double velPitchRatio_ = 1.0; // the velocity->pitch factor alone; retune re-applies it
     double pitchOffsetRatio_ = 1.0;  // the Pitch knob's factor — LIVE, re-applied by applyLive
     double rateRatio_ = 1.0;     // Rate's factor of the read increment; start() owns when it is 1
+    // Key-track, LATCHED at note-on beside the rate. Held here rather than re-read off the
+    // snapshot so a legato retune and a live block re-apply the note's own value; a published
+    // move reaches the next note only.
+    double keyTrack_ = kKeyTrackDefault;
     // Whether this note is ACTUALLY taking the Preserve read — a Preserve voice whose shifters
     // were never sized falls back to the varispeed one, and the two domains differ. Latched at
     // note-on beside rateRatio_, which start() resolves from the same predicate.

src/core/instrument/engine/voice_engine.cpp

@@ -56,9 +56,14 @@ void VoiceEngine::startVoice(Voice& voice, int note, int velocity) {
     refreshLive();
     // THE read of the note-on-latched commit class, and the only one: a published block outranks
     // the snapshot's own copy (a live edit deliberately leaves that stale), and applyLive below
-    // never touches the rate — so a Rate move reaches the next note and no sounding one.
+    // touches none of these three — so a move reaches the next note and no sounding one.
     const double rate = haveLive_ ? live_.playRate : sample_.play.playRate;
-    voice.start(note, velocity, sample_, /*declickTakeover=*/takeoverDeclick_, rate);
+    const double keyTrack = haveLive_ ? live_.keyTrack : sample_.keyTrack;
+    // Already spline-folded in the block; the snapshot branch folds here so the two agree.
+    const double lengthFraction =
+        haveLive_ ? live_.lengthFraction : effectiveLengthFraction(sample_.play);
+    voice.start(note, velocity, sample_, /*declickTakeover=*/takeoverDeclick_, rate, keyTrack,
+                lengthFraction);
     if (haveLive_) voice.applyLive(live_, /*snap=*/true);
     voice.setStartOrder(nextStartOrder_++);
 }