chore: import upstream snapshot with attribution

tests/unit/chatcore-request-setup.test.ts

@@ -0,0 +1,40 @@
+// tests/unit/chatcore-request-setup.test.ts
+// Characterization of resolveChatCoreRequestSetup — the first extracted pure slice of
+// chatCore's request-setup phase (god-file decomposition). Locks the structural-narrowing
+// of apiFormat/targetFormat and the requestedModel fallback.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { resolveChatCoreRequestSetup } from "../../open-sse/handlers/chatCore/requestSetup.ts";
+
+test("reads apiFormat / targetFormat only when present as strings", () => {
+  const r = resolveChatCoreRequestSetup(
+    { apiFormat: "responses", targetFormat: "openai" },
+    { model: "gpt-4o" },
+    "resolved-model"
+  );
+  assert.equal(r.apiFormat, "responses");
+  assert.equal(r.customModelTargetFormat, "openai");
+});
+
+test("apiFormat / targetFormat absent or non-string → undefined", () => {
+  assert.equal(resolveChatCoreRequestSetup({}, {}, "m").apiFormat, undefined);
+  assert.equal(resolveChatCoreRequestSetup({ apiFormat: 123 }, {}, "m").apiFormat, undefined);
+  assert.equal(resolveChatCoreRequestSetup({ targetFormat: null }, {}, "m").customModelTargetFormat, undefined);
+});
+
+test("modelInfo that is not an object → both markers undefined", () => {
+  const r = resolveChatCoreRequestSetup(null, { model: "x" }, "m");
+  assert.equal(r.apiFormat, undefined);
+  assert.equal(r.customModelTargetFormat, undefined);
+});
+
+test("requestedModel uses the client body.model when it is a non-blank string", () => {
+  assert.equal(resolveChatCoreRequestSetup({}, { model: "claude-3" }, "fallback").requestedModel, "claude-3");
+});
+
+test("requestedModel falls back to the resolved model id when body.model is blank/absent/non-string", () => {
+  assert.equal(resolveChatCoreRequestSetup({}, { model: "   " }, "fallback").requestedModel, "fallback");
+  assert.equal(resolveChatCoreRequestSetup({}, {}, "fallback").requestedModel, "fallback");
+  assert.equal(resolveChatCoreRequestSetup({}, { model: 42 }, "fallback").requestedModel, "fallback");
+  assert.equal(resolveChatCoreRequestSetup({}, null, "fallback").requestedModel, "fallback");
+});