fix(hopper): cancel startup before closing

tests/hopperClient.test.ts

@@ -254,4 +254,45 @@ describe("HopperClient", () => {
     expect(firstSettled).toBe(true);
     await first;
   });
+
+  it("does not finish startup after an immediate close", async () => {
+    const client = new HopperClient({
+      launcher: new FixtureLauncher(),
+      startupTimeoutMs: 1_000,
+    });
+    clients.push(client);
+
+    const starting = client.start();
+    await client.close();
+
+    const result = await starting;
+    expect(result.ok).toBe(false);
+    if (!result.ok) expect(result.error._tag).toBe("HopperCancelledError");
+  });
+
+  it("starts a fresh session after close completes", async () => {
+    const client = await startClient();
+    await client.close();
+
+    await expect(client.start()).resolves.toEqual({
+      ok: true,
+      value: { name: "REA Hopper bridge", version: "1.0.0" },
+    });
+  });
+
+  it("serializes a restart requested while close is in progress", async () => {
+    const client = await startClient();
+    const closing = client.close();
+    const restarting = client.start();
+
+    await closing;
+    await expect(restarting).resolves.toEqual({
+      ok: true,
+      value: { name: "REA Hopper bridge", version: "1.0.0" },
+    });
+    await expect(client.callTool("echo", { value: "fresh" })).resolves.toEqual({
+      ok: true,
+      value: { value: "fresh" },
+    });
+  });
 });