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/explorer-web/tests/e2e/explorer-live.spec.ts

@@ -0,0 +1,111 @@
+import { test, expect } from "@playwright/test";
+
+test.describe("Explorer live mode", () => {
+  test.beforeEach(async ({ page }) => {
+    await page.addInitScript(() => {
+      window.localStorage.setItem("aitbc-explorer:data-mode", "live");
+    });
+
+    await page.route("**/v1/explorer/blocks", async (route) => {
+      await route.fulfill({
+        status: 200,
+        contentType: "application/json",
+        body: JSON.stringify({
+          items: [
+            {
+              height: 12345,
+              hash: "0xabcdef1234567890",
+              timestamp: new Date("2024-08-22T12:00:00Z").toISOString(),
+              txCount: 12,
+              proposer: "validator-1",
+            },
+          ],
+          next_offset: null,
+        }),
+      });
+    });
+
+    await page.route("**/v1/explorer/transactions", async (route) => {
+      await route.fulfill({
+        status: 200,
+        contentType: "application/json",
+        body: JSON.stringify({
+          items: [
+            {
+              hash: "0xfeed1234",
+              block: 12345,
+              from: "0xAAA",
+              to: "0xBBB",
+              value: "0.50",
+              status: "Succeeded",
+            },
+          ],
+          next_offset: null,
+        }),
+      });
+    });
+
+    await page.route("**/v1/explorer/receipts", async (route) => {
+      await route.fulfill({
+        status: 200,
+        contentType: "application/json",
+        body: JSON.stringify({
+          jobId: "job-1",
+          items: [
+            {
+              receiptId: "receipt-1",
+              miner: "miner-1",
+              coordinator: "coordinator-1",
+              issuedAt: new Date("2024-08-22T12:00:00Z").toISOString(),
+              status: "Attested",
+            },
+          ],
+        }),
+      });
+    });
+
+    await page.route("**/v1/explorer/addresses", async (route) => {
+      await route.fulfill({
+        status: 200,
+        contentType: "application/json",
+        body: JSON.stringify({
+          items: [
+            {
+              address: "0xADDRESS",
+              balance: "100.0",
+              txCount: 42,
+              lastActive: new Date("2024-08-22T10:00:00Z").toISOString(),
+            },
+          ],
+          next_offset: null,
+        }),
+      });
+    });
+  });
+
+  test("overview renders live summaries", async ({ page }) => {
+    await page.goto("/");
+
+    await expect(page.locator("#overview-block-stats")).toContainText("12345");
+    await expect(page.locator("#overview-transaction-stats")).toContainText("Total Mock Tx: 1");
+    await expect(page.locator("#overview-receipt-stats")).toContainText("Total Receipts: 1");
+  });
+
+  test("blocks table shows live rows", async ({ page }) => {
+    await page.goto("/blocks");
+
+    const rows = page.locator("#blocks-table-body tr");
+    await expect(rows).toHaveCount(1);
+    await expect(rows.first()).toContainText("12345");
+    await expect(rows.first()).toContainText("validator-1");
+  });
+
+  test("transactions table shows live rows", async ({ page }) => {
+    await page.goto("/transactions");
+
+    const rows = page.locator("tbody tr");
+    await expect(rows).toHaveCount(1);
+    await expect(rows.first()).toContainText("0xfeed1234");
+    await expect(rows.first()).toContainText("Succeeded");
+  });
+});