feat(docker): Docker's own status reaches Steward — an empty answer clears a host, a lost one greys it, a demoted manager's swarm rows go (#5152)

The agent (1.9.0) said nothing when Docker could not be asked and nothing
when Docker had no containers, so Steward could tell neither apart from the
other, and kept a host's last containers on screen as running either way.

- Agent: collect_docker returns (status, detail, containers). "ok" sends
  docker: [] when there are none; "unavailable" (no socket, nothing
  listening) and "error" (permission, timeout, bad answer) say why.
  collect_swarm says whether /info answered, and a node that is not a
  manager sends swarm_manager: false. A failed /info says nothing.
- Ingest: an empty docker list is a snapshot; the newest sample's status
  goes to the Docker plugin with the rest.
- docker_host_status (docker_011): per host, status, detail, since and
  last report. A host that never had Docker gets no row.
- An "ok" empty snapshot reaps the host's containers; an error keeps them.
  swarm_manager: false drops the host's swarm services and nodes.
- Docker page: a "Docker not answering" card names each such host, why,
  and since when; its containers read as stale. Duplicate header comment
  in rows.html removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/docker/ingest.py

@@ -251,8 +251,37 @@ async def _persist_disk(session, host, disk: dict) -> None:
     await session.execute(stale)
 
 
+async def _persist_status(session, host, status: dict) -> None:
+    """Record whether Docker answered on this host, and why not.
+
+    A host reporting "unavailable" with no row yet never had Docker: nothing to
+    record. Once a host has had Docker, losing it is recorded, so its last
+    containers read as stale rather than as running."""
+    from .models import DockerHostStatus
+
+    row = await session.get(DockerHostStatus, host.id)
+    if row is None:
+        if status["status"] == "unavailable":
+            return
+        row = DockerHostStatus(host_id=host.id)
+        session.add(row)
+    if row.status != status["status"]:
+        row.since = status["at"]
+    row.status = status["status"]
+    row.detail = (status.get("detail") or "")[:255] or None
+    row.reported_at = status["at"]
+
+
+async def _expire_swarm(session, host) -> None:
+    """Drop the swarm rows a host reported while it was a manager."""
+    from .models import DockerSwarmNode, DockerSwarmService
+
+    await session.execute(delete(DockerSwarmService).where(DockerSwarmService.host_id == host.id))
+    await session.execute(delete(DockerSwarmNode).where(DockerSwarmNode.host_id == host.id))
+
+
 async def persist_host_docker(session, host, snapshots, swarm=None, disk=None,
-                              logs=None) -> None:
+                              logs=None, status=None) -> None:
     """Upsert containers + time-series + lifecycle events + swarm for one host.
 
     `snapshots` is a list of (recorded_at: datetime, containers: list[dict]) —
@@ -264,11 +293,18 @@ async def persist_host_docker(session, host, snapshots, swarm=None, disk=None,
     `disk` is the newest sample's /system/df summary (or None on Docker-less
     hosts) — persisted when present. `logs` is a list of (recorded_at, records)
     log batches (m79) — appended one row per line when present, independent of
-    whether this sample also carried container metrics.
+    whether this sample also carried container metrics. `status` is the newest
+    sample's {"status", "detail", "at", "swarm_manager"} (agent ≥ 1.9.0): an
+    "ok" with an empty snapshot clears the host's containers, and a node that
+    says it is no longer a manager loses the swarm rows it reported as one.
     """
     from steward.core.alerts import MetricBatch
     from .models import DockerContainer, DockerEvent, DockerMetric
 
+    if status is not None:
+        await _persist_status(session, host, status)
+        if status.get("swarm_manager") is False:
+            await _expire_swarm(session, host)
     if swarm is not None:
         await _persist_swarm(session, host, swarm)
     if disk is not None: