fix(align): render at 44.1k and resample; finite guard; pre-zero tests

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/align/render.test.ts

@@ -7,7 +7,7 @@ import type { RefTrack, RefNote } from "../../src/align/smf.ts";
 const SF2 = new Uint8Array(await Bun.file("node_modules/@coderline/alphatab/dist/soundfont/sonivox.sf2").arrayBuffer());
 const note = (onset: number, offset: number, pitch: number): RefNote => ({ onset, offset, pitch, velocity: 100, channel: 0 });
 const track = (notes: RefNote[], isDrums = false): RefTrack => ({ index: 0, name: "t", program: 25, isDrums, notes });
-const SR = 44100; // alphaSynth yields NaN at 22050 Hz
+const SR = 44100;
 
 function firstAbove(x: Float32Array, thr: number): number {
   for (let i = 0; i < x.length; i++) if (Math.abs(x[i]!) > thr) return i;
@@ -49,3 +49,29 @@ test("peaks of a known sine", () => {
   expect([...q.max]).toEqual([0.5, 0]);
   expect([...q.min]).toEqual([0.25, -0.75]);
 });
+
+test("sampleRate 22050 is finite, at 22050 Hz, onset preserved", () => {
+  const a = renderMidi([track([note(1, 2, 60)])], makeWarp([{ midiSec: 0, audioSec: 0.5, kind: "manual" }]), SF2, { sampleRate: 22050, mono: true, durationSec: 4 });
+  expect(a.sampleRate).toBe(22050);
+  expect(a.channels[0]!.length).toBe(4 * 22050);
+  expect(a.channels[0]!.every(Number.isFinite)).toBe(true);
+  const t = firstAbove(a.channels[0]!, 0.02) / 22050;
+  expect(t).toBeGreaterThan(1.48);
+  expect(t).toBeLessThan(1.52);
+});
+
+test("notes before audio zero: clamped when overlapping, dropped when entirely before", () => {
+  const w = makeWarp([{ midiSec: 1, audioSec: 0, kind: "manual" }]); // audio = midi - 1
+  const dropped = renderMidi([track([note(0, 0.5, 60)]), track([note(2, 2.5, 64)])], w, SF2, { durationSec: 3 });
+  const t = firstAbove(dropped.channels[0]!, 0.02) / 44100;
+  expect(t).toBeGreaterThan(0.98);
+  const clamped = renderMidi([track([note(0.5, 2, 60)])], w, SF2, { durationSec: 3 });
+  expect(firstAbove(clamped.channels[0]!, 0.02) / 44100).toBeLessThan(0.05);
+});
+
+test("stereo with durationSec has two channels of exact length", () => {
+  const a = renderMidi([track([note(0, 0.5, 60)])], makeWarp([]), SF2, { durationSec: 2 });
+  expect(a.channels.length).toBe(2);
+  expect(a.channels[0]!.length).toBe(88200);
+  expect(a.channels[1]!.length).toBe(88200);
+});