Apply item 0xe5e8732a for issue #2

Squash of the patch of item 0xe5e8732a047e9b487e856f47bfd4a96074d25264d0ab22897c8d7106fa6316da, final in the elffuss ledger.
Solver 0x3c4b6c950e8bf72399a3f54c7141ed8c487a9daf; 2 approvals of round 0.

T2T-Item: 0xe5e8732a047e9b487e856f47bfd4a96074d25264d0ab22897c8d7106fa6316da
T2T-Issue: 0x09060fd098e76bfb06be9362ac725843d1834d9218762843b41c83830b66a5c3
T2T-Event: 0xa3f482bef7a2d33d74d754067c3a813488b24309cb56d1040c422d7704d25908

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: vectors must have the same 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);
+});