Mock sendRequest in session.resume unit tests

These tests verify that the correct parameters are forwarded to the RPC
call, not that the CLI handles them. Mock sendRequest (like the setModel
test already does) so the tests don't depend on CLI authentication,
which is unavailable on fork PRs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

nodejs/test/client.test.ts

@@ -68,7 +68,13 @@ describe("CopilotClient", () => {
         onTestFinished(() => client.forceStop());
 
         const session = await client.createSession({ onPermissionRequest: approveAll });
-        const spy = vi.spyOn((client as any).connection!, "sendRequest");
+        // Mock sendRequest to capture the call without hitting the runtime
+        const spy = vi
+            .spyOn((client as any).connection!, "sendRequest")
+            .mockImplementation(async (method: string, params: any) => {
+                if (method === "session.resume") return { sessionId: params.sessionId };
+                throw new Error(`Unexpected method: ${method}`);
+            });
         await client.resumeSession(session.sessionId, {
             clientName: "my-app",
             onPermissionRequest: approveAll,
@@ -78,6 +84,7 @@ describe("CopilotClient", () => {
             "session.resume",
             expect.objectContaining({ clientName: "my-app", sessionId: session.sessionId })
         );
+        spy.mockRestore();
     });
 
     it("sends session.model.switchTo RPC with correct params", async () => {
@@ -325,7 +332,13 @@ describe("CopilotClient", () => {
             onTestFinished(() => client.forceStop());
 
             const session = await client.createSession({ onPermissionRequest: approveAll });
-            const spy = vi.spyOn((client as any).connection!, "sendRequest");
+            // Mock sendRequest to capture the call without hitting the runtime
+            const spy = vi
+                .spyOn((client as any).connection!, "sendRequest")
+                .mockImplementation(async (method: string, params: any) => {
+                    if (method === "session.resume") return { sessionId: params.sessionId };
+                    throw new Error(`Unexpected method: ${method}`);
+                });
             await client.resumeSession(session.sessionId, {
                 onPermissionRequest: approveAll,
                 tools: [
@@ -342,6 +355,7 @@ describe("CopilotClient", () => {
             expect(payload.tools).toEqual([
                 expect.objectContaining({ name: "grep", overridesBuiltInTool: true }),
             ]);
+            spy.mockRestore();
         });
     });
 });