chore: import upstream snapshot with attribution

tests/unit/combo-hedging.test.ts

@@ -0,0 +1,66 @@
+/**
+ * tests/unit/combo-hedging.test.ts
+ *
+ * Previously a placeholder (two `assert.ok(true)`). Now exercises the two
+ * zero-latency features it claims to cover:
+ *   1. Predictive-TTFT circuit-breaker DECISION (shouldSkipForPredictedTtft).
+ *   2. Hedging / zero-latency CONFIG resolution (defaults + per-combo override),
+ *      i.e. the knobs the combo engine reads before racing/skip-ahead.
+ *
+ * The full hedging DISPATCH (Promise.race + loser abort) is covered end-to-end
+ * in combo-routing-engine.test.ts; here we pin the decision logic + config
+ * plumbing that gate it (both opt-in / off by default).
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import { shouldSkipForPredictedTtft } from "../../open-sse/services/combo.ts";
+import { getDefaultComboConfig, resolveComboConfig } from "../../open-sse/services/comboConfig.ts";
+
+// ── Predictive-TTFT circuit breaker (decision) ────────────────────────────────
+test("predictive-TTFT — skips a model whose avg latency exceeds the ceiling (enough samples)", () => {
+  assert.equal(shouldSkipForPredictedTtft({ requests: 10, avgLatencyMs: 5000 }, 2000), true);
+});
+
+test("predictive-TTFT — does NOT skip with too few samples (< 5)", () => {
+  assert.equal(shouldSkipForPredictedTtft({ requests: 4, avgLatencyMs: 9000 }, 2000), false);
+});
+
+test("predictive-TTFT — does NOT skip when avg latency is within the ceiling", () => {
+  assert.equal(shouldSkipForPredictedTtft({ requests: 50, avgLatencyMs: 1200 }, 2000), false);
+});
+
+test("predictive-TTFT — disabled (ceiling <= 0) never skips", () => {
+  assert.equal(shouldSkipForPredictedTtft({ requests: 50, avgLatencyMs: 9000 }, 0), false);
+});
+
+test("predictive-TTFT — null/missing metric never skips", () => {
+  assert.equal(shouldSkipForPredictedTtft(null, 2000), false);
+  assert.equal(shouldSkipForPredictedTtft(undefined, 2000), false);
+});
+
+// ── Hedging / zero-latency config resolution ──────────────────────────────────
+test("hedging — defaults are opt-in (off) so normal combos never race", () => {
+  const d = getDefaultComboConfig();
+  assert.equal(d.hedging, false);
+  assert.equal(d.hedgeDelayMs, 500);
+  assert.equal(d.predictiveTtftMs, 0);
+  assert.equal(d.zeroLatencyOptimizationsEnabled, false);
+});
+
+test("hedging — per-combo config overrides the zero-latency defaults", () => {
+  const resolved = resolveComboConfig(
+    {
+      config: {
+        hedging: true,
+        hedgeDelayMs: 200,
+        zeroLatencyOptimizationsEnabled: true,
+        predictiveTtftMs: 3000,
+      },
+    },
+    null
+  );
+  assert.equal(resolved.hedging, true);
+  assert.equal(resolved.hedgeDelayMs, 200);
+  assert.equal(resolved.zeroLatencyOptimizationsEnabled, true);
+  assert.equal(resolved.predictiveTtftMs, 3000);
+});