✅ test: add edge case tests for throttle and semaphore

- throttle: consume(0) resolves immediately
- throttle: updateRate(0) makes consume instant (unlimited)
- semaphore: release without acquire clamps active to 0

All 66 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/semaphore.test.js

@@ -162,4 +162,13 @@ describe('Semaphore', () => {
     await new Promise(r => setTimeout(r, 5));
     assert.equal(sem.pending, 1);
   });
+
+  it('release without acquire clamps active to 0', () => {
+    const sem = new Semaphore(2);
+    assert.equal(sem.active, 0);
+    sem.release();
+    assert.equal(sem.active, 0, 'should not go negative');
+    sem.release();
+    assert.equal(sem.active, 0, 'should still be 0');
+  });
 });

tests/throttle.test.js

@@ -83,4 +83,19 @@ describe('Throttle', () => {
     const elapsed = Date.now() - start2;
     assert.ok(elapsed >= 150, `third consume should wait for refill, took ${elapsed}ms`);
   });
+
+  it('consume(0) resolves immediately', async () => {
+    const t = new Throttle(100);
+    const start = Date.now();
+    await t.consume(0);
+    assert.ok(Date.now() - start < 50);
+  });
+
+  it('updateRate to unlimited (0) makes consume instant', async () => {
+    const t = new Throttle(100); // very slow
+    t.updateRate(0); // unlimited
+    const start = Date.now();
+    await t.consume(1_000_000);
+    assert.ok(Date.now() - start < 50, 'unlimited rate should be instant');
+  });
 });