chore: import upstream snapshot with attribution

tests/unit/mitm-handler-codex.test.ts

@@ -0,0 +1,17 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { CodexHandler } from "../../src/mitm/handlers/codex.ts";
+import { runHandler } from "./_mitmHandlerHarness.ts";
+
+test("codex handler — forwards Chat Completions payload via OmniRoute", async () => {
+  const r = await runHandler(
+    new CodexHandler(),
+    { model: "gpt-4.1", messages: [] },
+    "gpt-4o-mini"
+  );
+  assert.ok(r.fetchCalled);
+  assert.equal(r.status, 200);
+  assert.ok(r.fetchUrl?.endsWith("/v1/chat/completions"));
+  const sent = JSON.parse(r.fetchBody);
+  assert.equal(sent.model, "gpt-4o-mini");
+});