feat: honor canonical glide time for slide notes

src/engine/SynthEngine.ts

@@ -69,6 +69,10 @@ function linearGainToDb(value: number): number {
   return 20 * Math.log10(Math.max(MIN_LINEAR_GAIN, value));
 }
 
+function getLegacySlidePortamentoSeconds(duration: number): number {
+  return Math.max(0.03, Math.min(0.12, duration * 0.35));
+}
+
 function toLegacySubtractivePreset(preset: SynthPreset): LegacySynthVoicePreset {
   return preset === 'sampler' ? 'piano' : preset;
 }
@@ -223,6 +227,17 @@ export function createSynthRuntimeSpec(source: SynthSource): SynthRuntimeSpec {
   return createSubtractiveRuntimeSpec(resolveSubtractiveInstrument(source));
 }
 
+export function resolveSlidePortamentoSeconds(source: SynthSource, duration: number): number {
+  const spec = createSynthRuntimeSpec(source);
+  const configured = typeof spec.options.portamento === 'number'
+    ? Math.max(0, spec.options.portamento)
+    : 0;
+
+  return configured > 0
+    ? configured
+    : getLegacySlidePortamentoSeconds(duration);
+}
+
 export function createSynthModulationSpec(source: SynthSource): SynthModulationSpec | null {
   const instrument = resolveSubtractiveLfoInstrument(source);
   if (!instrument) return null;
@@ -506,7 +521,7 @@ class SynthEngine {
       triggerAttackRelease: (note: number, duration: number, time?: string | number, velocity?: number) => void;
     };
     restartPlaybackModulation(this.synths.get(trackId));
-    const glideTime = Math.max(0.03, Math.min(0.12, duration * 0.35));
+    const glideTime = resolveSlidePortamentoSeconds(source, duration);
     const fromFreq = Tone.Frequency(fromPitch, 'midi').toFrequency();
     const toFreq = Tone.Frequency(toPitch, 'midi').toFrequency();
     synth.set({ portamento: glideTime });

src/engine/__tests__/SynthEngine.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest';
-import { createSynthModulationSpec, createSynthRuntimeSpec } from '../SynthEngine';
+import { createSynthModulationSpec, createSynthRuntimeSpec, resolveSlidePortamentoSeconds } from '../SynthEngine';
 import {
   createDefaultFmInstrument,
   createDefaultSamplerInstrument,
@@ -244,3 +244,28 @@ describe('createSynthModulationSpec', () => {
     expect(options.depth).toBeCloseTo(0.85, 5);
   });
 });
+
+describe('resolveSlidePortamentoSeconds', () => {
+  it('uses canonical subtractive glide time when a positive glide value is configured', () => {
+    const instrument = createDefaultSubtractiveInstrument('lead', {
+      settings: {
+        glideTime: 0.48,
+      },
+    });
+
+    expect(resolveSlidePortamentoSeconds(instrument, 0.2)).toBeCloseTo(0.48, 5);
+  });
+
+  it('falls back to the legacy slide heuristic for zero-glide subtractive, FM, and preset sources', () => {
+    const subtractive = createDefaultSubtractiveInstrument('pad', {
+      settings: {
+        glideTime: 0,
+      },
+    });
+    const fm = createDefaultFmInstrument();
+
+    expect(resolveSlidePortamentoSeconds(subtractive, 0.5)).toBeCloseTo(0.12, 5);
+    expect(resolveSlidePortamentoSeconds(fm, 0.4)).toBeCloseTo(0.12, 5);
+    expect(resolveSlidePortamentoSeconds('lead', 0.04)).toBeCloseTo(0.03, 5);
+  });
+});