chore: import upstream snapshot with attribution

tests/unit/chatcore-failure-usage.test.ts

@@ -0,0 +1,79 @@
+// tests/unit/chatcore-failure-usage.test.ts
+// Characterization of buildFailureUsageRecord — the failed-request usage payload builder extracted
+// from handleChatCore's persistFailureUsage closure (chatCore god-file decomposition, #3501). Pure:
+// the handler keeps the fire-and-forget saveRequestUsage(...).catch() call and computes latencyMs;
+// this builds the record. Locks the unknown/undefined fallbacks, the zeroed token/timing fields,
+// the combo-strategy gate, and the ISO timestamp.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { buildFailureUsageRecord } from "../../open-sse/handlers/chatCore/failureUsage.ts";
+
+const ISO = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/;
+
+test("maps a fully-populated failure into the usage record", () => {
+  const r = buildFailureUsageRecord({
+    provider: "openai",
+    model: "gpt-4o",
+    connectionId: "conn-1",
+    apiKeyInfo: { id: "key-1", name: "My Key" },
+    effectiveServiceTier: "priority",
+    isCombo: true,
+    comboStrategy: "weighted",
+    statusCode: 429,
+    errorCode: "rate_limited",
+    latencyMs: 1234,
+  });
+  assert.equal(r.provider, "openai");
+  assert.equal(r.model, "gpt-4o");
+  assert.deepEqual(r.tokens, { input: 0, output: 0, cacheRead: 0, cacheCreation: 0, reasoning: 0 });
+  assert.equal(r.status, "429");
+  assert.equal(r.success, false);
+  assert.equal(r.latencyMs, 1234);
+  assert.equal(r.timeToFirstTokenMs, 0);
+  assert.equal(r.errorCode, "rate_limited");
+  assert.match(String(r.timestamp), ISO);
+  assert.equal(r.connectionId, "conn-1");
+  assert.equal(r.apiKeyId, "key-1");
+  assert.equal(r.apiKeyName, "My Key");
+  assert.equal(r.serviceTier, "priority");
+  assert.equal(r.comboStrategy, "weighted");
+});
+
+test("applies the unknown/undefined fallbacks", () => {
+  const r = buildFailureUsageRecord({
+    provider: null,
+    model: undefined,
+    connectionId: null,
+    apiKeyInfo: null,
+    effectiveServiceTier: "standard",
+    isCombo: false,
+    comboStrategy: "priority",
+    statusCode: 502,
+    errorCode: null,
+    latencyMs: 7,
+  });
+  assert.equal(r.provider, "unknown");
+  assert.equal(r.model, "unknown");
+  assert.equal(r.errorCode, "502"); // falls back to String(statusCode)
+  assert.equal(r.connectionId, undefined);
+  assert.equal(r.apiKeyId, undefined);
+  assert.equal(r.apiKeyName, undefined);
+  // isCombo false → comboStrategy is dropped even when supplied
+  assert.equal(r.comboStrategy, undefined);
+});
+
+test("combo strategy is included only for combo requests", () => {
+  const combo = buildFailureUsageRecord({
+    provider: "x", model: "y", connectionId: null, apiKeyInfo: null,
+    effectiveServiceTier: "standard", isCombo: true, comboStrategy: "round-robin",
+    statusCode: 500, errorCode: "boom", latencyMs: 1,
+  });
+  assert.equal(combo.comboStrategy, "round-robin");
+
+  const comboNoStrategy = buildFailureUsageRecord({
+    provider: "x", model: "y", connectionId: null, apiKeyInfo: null,
+    effectiveServiceTier: "standard", isCombo: true, comboStrategy: null,
+    statusCode: 500, errorCode: "boom", latencyMs: 1,
+  });
+  assert.equal(comboNoStrategy.comboStrategy, undefined);
+});