Based on the repository's commit message style and the changes in the diff, here's an appropriate commit message:

```
feat: add websocket tests, PoA metrics, marketplace endpoints, and enhanced observability

- Add comprehensive websocket tests for blocks and transactions streams including multi-subscriber and high-volume scenarios
- Extend PoA consensus with per-proposer block metrics and rotation tracking
- Add latest block interval gauge and RPC error spike alerting
- Enhance mock coordinator

apps/marketplace-web/src/counter.ts

@@ -0,0 +1,9 @@
+export function setupCounter(element: HTMLButtonElement) {
+  let counter = 0
+  const setCounter = (count: number) => {
+    counter = count
+    element.innerHTML = `count is ${counter}`
+  }
+  element.addEventListener('click', () => setCounter(counter + 1))
+  setCounter(0)
+}