chore: import upstream snapshot with attribution

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

@@ -0,0 +1,21 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { CopilotHandler } from "../../src/mitm/handlers/copilot.ts";
+import { runHandler } from "./_mitmHandlerHarness.ts";
+
+test("copilot handler — rewrites model and forwards to /v1/chat/completions", async () => {
+  const r = await runHandler(
+    new CopilotHandler(),
+    { model: "gpt-4o", messages: [] },
+    "claude-3.5-sonnet"
+  );
+  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, "claude-3.5-sonnet");
+  // AgentBridge correlation headers must be present.
+  const headers = r.fetchHeaders as Record<string, string>;
+  assert.equal(headers["x-omniroute-source"], "agent-bridge");
+  assert.equal(headers["x-omniroute-agent"], "copilot");
+});