Report the instrument's automatable parameters to the host under a frozen id table, in signal-flow order, with real units

42 of 44 ids issued: pitch key-track and Trigger length stay reserved
pending a live path. Master gain reclassified Live — it never reloaded.

src/core/instrument/param/param_units.h

@@ -0,0 +1,64 @@
+// param_units.h — the plain-value layer the host reads a parameter through: the unit category,
+// the plain range, and the norm <-> plain pair. `toPlain` IS the taper's forward map and
+// `toNormalized` its inverse, so the host's normalization, the knob's needle angle and the
+// overlay node's position are the SAME function rather than three that agree today.
+
+#pragma once
+
+#include "core/instrument/ui/deck_groups.h"  // DeckParam
+
+namespace reasampler::instrument::param {
+
+using ui::DeckParam;
+
+// The eight DISPLAY categories. A category fixes the units string and the digit precision; the
+// norm <-> plain LAW is per control, because three of the dimensionless controls (the curve
+// exponents, Q, drive) share a display and share no law.
+enum class UnitKind {
+    Time,             // ms, 0..10000
+    Semitones,        // st, -24..+24, always signed
+    PercentUnipolar,  // %, 0..100
+    PercentKeyTrack,  // %, 0..200
+    PercentBipolar,   // %, -100..+100, always signed
+    PercentRate,      // %, 50..200, one decimal
+    Decibels,         // dB, -60..+24, always signed; norm 0 reads -inf
+    Hertz,            // Hz, 20..20000
+    Dimensionless,    // no unit, two decimals
+};
+
+struct PlainRange {
+    double min = 0.0;
+    double max = 1.0;
+};
+
+UnitKind unitKindFor(DeckParam deck);
+
+// The units string ParameterInfo carries — "" for the dimensionless category. Carried SEPARATELY
+// from the digits, which is the SDK's own convention (RangeParameter::toString prints the number;
+// the Parameter constructor takes units as its own argument).
+const char* unitStringFor(DeckParam deck);
+
+PlainRange plainRangeFor(DeckParam deck);
+
+// A straight line drawn in a host automation lane is NOT linear in these plain units, and that is
+// deliberate: exponential in ms, linear in octaves on cutoff, linear in dB on master gain, a
+// linear pitch glide on rate, and slow-near-zero on the two centre-expanded semitone throws. It
+// follows from reporting real units over a musically-shaped taper; the remedy for a user who
+// wants a literal-units ramp is the host's own curve tools, never a change to the taper.
+double toPlain(DeckParam deck, double normalized);
+double toNormalized(DeckParam deck, double plain);
+
+// The filter's four tone controls STORE their normalized position (payload v9), so their default
+// normalized value is that stored double verbatim and no taper participates in a host's
+// reset-to-default. Reporting Hz / Q / drive depth for them means CALLING their frozen laws, not
+// replacing them.
+bool storesNormalized(DeckParam deck);
+
+// The default, read off a default-constructed PlaySeconds — there is no second table of defaults,
+// and no normalized default is ever written as a literal. defaultNormalized is COMPUTED as
+// toNormalized(defaultPlain) for every tapered control, which is what makes a host's
+// reset-to-default and the editor's double-click land on the same value.
+double defaultPlain(DeckParam deck);
+double defaultNormalized(DeckParam deck);
+
+}  // namespace reasampler::instrument::param