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/public/mock/offers.json

@@ -0,0 +1,36 @@
+{
+  "offers": [
+    {
+      "id": "offer-101",
+      "provider": "Alpha Pool",
+      "capacity": 250,
+      "price": 12.5,
+      "sla": "99.9%",
+      "status": "Open"
+    },
+    {
+      "id": "offer-102",
+      "provider": "Beta Collective",
+      "capacity": 140,
+      "price": 15.75,
+      "sla": "99.5%",
+      "status": "Open"
+    },
+    {
+      "id": "offer-103",
+      "provider": "Gamma Compute",
+      "capacity": 400,
+      "price": 10.9,
+      "sla": "99.95%",
+      "status": "Reserved"
+    },
+    {
+      "id": "offer-104",
+      "provider": "Delta Grid",
+      "capacity": 90,
+      "price": 18.25,
+      "sla": "99.0%",
+      "status": "Open"
+    }
+  ]
+}

apps/marketplace-web/public/mock/stats.json

@@ -0,0 +1,6 @@
+{
+  "totalOffers": 78,
+  "openCapacity": 1120,
+  "averagePrice": 14.3,
+  "activeBids": 36
+}