Apply item 0xa95f32ea for issue #2

Squash of the patch of item 0xa95f32ea03bfe95df656140edb88432fac22efa32917418f73d0f29ce155ecd0, final in the elffuss ledger.
Solver 0xeb104004d5d1c1f091d70119cbfe17b6370433f1; 2 approvals of round 0.

T2T-Item: 0xa95f32ea03bfe95df656140edb88432fac22efa32917418f73d0f29ce155ecd0
T2T-Issue: 0xc0ae452fd36bac337ec3f451e6383702e4d49a1fb1113ea26024dff8f4d296c1
T2T-Event: 0xb52e3d5f828c1af808612b98fd666596d74eba5a9b707c9b50edc4495e360024

diarize.mjs

@@ -25,7 +25,7 @@ export async function loadDiarizer(TF, { device = 'wasm' } = {}) {
   return { seg, segP, emb, embP };
 }
 
-const cos = (a, b) => { let dt = 0, na = 0, nb = 0; for (let i = 0; i < a.length; i++) { dt += a[i]*b[i]; na += a[i]*a[i]; nb += b[i]*b[i]; } return dt / (Math.sqrt(na)*Math.sqrt(nb) || 1); };
+const cos = (a, b) => { if (a.length !== b.length) throw new Error(`cosine: length mismatch (${a.length} vs ${b.length})`); let dt = 0, na = 0, nb = 0; for (let i = 0; i < a.length; i++) { dt += a[i]*b[i]; na += a[i]*a[i]; nb += b[i]*b[i]; } return dt / (Math.sqrt(na)*Math.sqrt(nb) || 1); };
 const rms = (a) => { let s = 0; for (const v of a) s += v*v; return Math.sqrt(s/a.length); };
 
 async function embed(D, slice) {

tests/acceptance/2/CRITERIA.json

@@ -0,0 +1,18 @@
+{
+  "schema": "elffuss-t2t/criteria@2",
+  "issue": 2,
+  "criteria": [
+    {
+      "index": 1,
+      "tests": [
+        "tests/acceptance/2/criteria.test.js::criterion 1"
+      ]
+    },
+    {
+      "index": 2,
+      "tests": [
+        "tests/acceptance/2/criteria.test.js::criterion 2"
+      ]
+    }
+  ]
+}

tests/acceptance/2/criteria.test.js

@@ -0,0 +1,13 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+const mod = await import('../../../diarize.mjs');
+
+test('criterion 1', () => {
+  assert.throws(() => mod.cosine([1, 2, 3], [1, 2]), (err) => err instanceof Error && err.message.startsWith('cosine:'));
+  assert.equal(mod.cosine([1, 0], [1, 0]), 1);
+});
+
+test('criterion 2', () => {
+  assert.throws(() => mod.cosine([1, 0], [1, 0, 5]), (err) => err instanceof Error && err.message.startsWith('cosine:'));
+  assert.equal(mod.cosine([0, 0], [0, 0]), 0);
+});