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/coordinator-api/src/app/routers/__init__.py

@@ -1 +1,9 @@
 """Router modules for the coordinator API."""
+
+from .client import router as client
+from .miner import router as miner
+from .admin import router as admin
+from .marketplace import router as marketplace
+from .explorer import router as explorer
+
+__all__ = ["client", "miner", "admin", "marketplace", "explorer"]

apps/coordinator-api/src/app/routers/explorer.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+from fastapi import APIRouter, Depends, Query
+
+from ..models import (
+    BlockListResponse,
+    TransactionListResponse,
+    AddressListResponse,
+    ReceiptListResponse,
+)
+from ..services import ExplorerService
+from ..storage import SessionDep
+
+router = APIRouter(prefix="/explorer", tags=["explorer"])
+
+
+def _service(session: SessionDep) -> ExplorerService:
+    return ExplorerService(session)
+
+
+@router.get("/blocks", response_model=BlockListResponse, summary="List recent blocks")
+async def list_blocks(
+    *,
+    session: SessionDep,
+    limit: int = Query(default=20, ge=1, le=200),
+    offset: int = Query(default=0, ge=0),
+) -> BlockListResponse:
+    return _service(session).list_blocks(limit=limit, offset=offset)
+
+
+@router.get(
+    "/transactions",
+    response_model=TransactionListResponse,
+    summary="List recent transactions",
+)
+async def list_transactions(
+    *,
+    session: SessionDep,
+    limit: int = Query(default=50, ge=1, le=200),
+    offset: int = Query(default=0, ge=0),
+) -> TransactionListResponse:
+    return _service(session).list_transactions(limit=limit, offset=offset)
+
+
+@router.get("/addresses", response_model=AddressListResponse, summary="List address summaries")
+async def list_addresses(
+    *,
+    session: SessionDep,
+    limit: int = Query(default=50, ge=1, le=200),
+    offset: int = Query(default=0, ge=0),
+) -> AddressListResponse:
+    return _service(session).list_addresses(limit=limit, offset=offset)
+
+
+@router.get("/receipts", response_model=ReceiptListResponse, summary="List job receipts")
+async def list_receipts(
+    *,
+    session: SessionDep,
+    job_id: str | None = Query(default=None, description="Filter by job identifier"),
+    limit: int = Query(default=50, ge=1, le=200),
+    offset: int = Query(default=0, ge=0),
+) -> ReceiptListResponse:
+    return _service(session).list_receipts(job_id=job_id, limit=limit, offset=offset)

apps/coordinator-api/src/app/routers/marketplace.py

@@ -0,0 +1,57 @@
+from __future__ import annotations
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi import status as http_status
+
+from ..models import MarketplaceBidRequest, MarketplaceOfferView, MarketplaceStatsView
+from ..services import MarketplaceService
+from ..storage import SessionDep
+
+router = APIRouter(tags=["marketplace"])
+
+
+def _get_service(session: SessionDep) -> MarketplaceService:
+    return MarketplaceService(session)
+
+
+@router.get(
+    "/marketplace/offers",
+    response_model=list[MarketplaceOfferView],
+    summary="List marketplace offers",
+)
+async def list_marketplace_offers(
+    *,
+    session: SessionDep,
+    status_filter: str | None = Query(default=None, alias="status", description="Filter by offer status"),
+    limit: int = Query(default=100, ge=1, le=500),
+    offset: int = Query(default=0, ge=0),
+) -> list[MarketplaceOfferView]:
+    service = _get_service(session)
+    try:
+        return service.list_offers(status=status_filter, limit=limit, offset=offset)
+    except ValueError:
+        raise HTTPException(status_code=http_status.HTTP_400_BAD_REQUEST, detail="invalid status filter") from None
+
+
+@router.get(
+    "/marketplace/stats",
+    response_model=MarketplaceStatsView,
+    summary="Get marketplace summary statistics",
+)
+async def get_marketplace_stats(*, session: SessionDep) -> MarketplaceStatsView:
+    service = _get_service(session)
+    return service.get_stats()
+
+
+@router.post(
+    "/marketplace/bids",
+    status_code=http_status.HTTP_202_ACCEPTED,
+    summary="Submit a marketplace bid",
+)
+async def submit_marketplace_bid(
+    payload: MarketplaceBidRequest,
+    session: SessionDep,
+) -> dict[str, str]:
+    service = _get_service(session)
+    bid = service.create_bid(payload)
+    return {"id": bid.id}