feat(mcp): docker and host-agent tools; TLS and crash-loop cutoffs in Settings

MCP-5 of milestone 461 "MCP server: Steward as an LLM-inspectable,
LLM-operable hub". Contributed through each plugin's register_mcp_tools
hook, so they exist only while the plugin is enabled.

docker (viewer, read-only):
- list_containers: filter by host, status, compose project, or problem
  (restarting, crash_looping, unhealthy, oom_killed, exited_nonzero);
  problems sort first and each row names what is wrong.
- get_container: state, CPU/memory history across the raw/hourly seam,
  lifecycle events. A unique part of a swarm task name is enough.
- list_swarm_services: replicas per node (agent-less placements as ghosts)
  and the swarm's nodes.
- search_container_logs: text (% and _ literal), stream, range, context
  lines, paging by a full-precision `before` cursor; over-long lines keep
  both ends and say how much of the middle was cut.
- get_docker_disk_usage: bytes per host, reclaimable first.
- mcp_overview: failing containers and under-replicated swarm services
  join get_overview.

host_agent: list_agents (reporting / stale / pending, version, OS), and an
overview finding for agents registered over 30 minutes ago that never
checked in.

Settings > Thresholds gains the TLS-expiry warn/crit days (were 14/3 in
code) and the crash-loop deaths-per-hour count (3), which get_overview
and the docker tools now read.

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

plugins/docker/service.py

@@ -6,11 +6,12 @@ Quart's pipeline) call the same code.
 """
 from __future__ import annotations
 
-from sqlalchemy import select
+from sqlalchemy import func, select
 
+from steward.core.time_range import bucket_seconds
 from steward.models.hosts import Host
 
-from .models import DockerContainer, DockerEvent, DockerLog, DockerMetric
+from .models import DockerContainer, DockerEvent, DockerLog, DockerMetric, DockerMetricHourly
 
 
 def bucket(values: list[float], target: int = 40) -> list[float]:
@@ -97,3 +98,88 @@ async def query_logs(db, host_id: str, name: str, stream: str, query: str,
         stmt = stmt.where(DockerLog.line.ilike(f"%{escape_like(query)}%", escape="\\"))
     stmt = stmt.order_by(DockerLog.ts.desc(), DockerLog.id.desc()).limit(limit)
     return (await db.execute(stmt)).all()
+
+
+CONTAINER_SERIES = ("cpu_pct", "mem_pct", "mem_usage_bytes")
+
+
+async def container_points(db, host_id: str, name: str, metric: str, since,
+                           target: int = 120) -> list[tuple]:
+    """(time, average) points of one container metric since `since`, oldest first.
+
+    Raw samples are bucket-averaged in SQL; the part of the range older than
+    the oldest raw sample (already rolled up and pruned by retention) comes
+    from the hourly table.
+    """
+    if metric not in CONTAINER_SERIES:
+        raise ValueError(f"metric must be one of {', '.join(CONTAINER_SERIES)}")
+    raw_col = getattr(DockerMetric, metric)
+    width_s = bucket_seconds(since, target)
+    rbucket = func.date_bin(
+        func.make_interval(0, 0, 0, 0, 0, 0, width_s), DockerMetric.scraped_at, func.to_timestamp(0),
+    ).label("bucket")
+    raw = (await db.execute(
+        select(rbucket, func.avg(raw_col))
+        .where(DockerMetric.host_id == host_id, DockerMetric.container_name == name,
+               DockerMetric.scraped_at >= since)
+        .group_by(rbucket).order_by(rbucket)
+    )).all()
+    oldest_raw = raw[0][0] if raw else None
+    hourly_stmt = (
+        select(DockerMetricHourly.bucket, getattr(DockerMetricHourly, metric))
+        .where(DockerMetricHourly.host_id == host_id,
+               DockerMetricHourly.container_name == name,
+               DockerMetricHourly.bucket >= since)
+        .order_by(DockerMetricHourly.bucket)
+    )
+    if oldest_raw is not None:
+        hourly_stmt = hourly_stmt.where(DockerMetricHourly.bucket < oldest_raw)
+    hourly = (await db.execute(hourly_stmt)).all()
+    return [(t, float(v)) for t, v in hourly] + [(t, float(v)) for t, v in raw]
+
+
+async def search_logs(db, *, since, host_id: str | None = None, name: str | None = None,
+                      text: str = "", stream: str = "", before=None, limit: int = 50) -> list:
+    """Retained log lines matching a filter, newest first (limit + 1 fetched by callers
+    that need to know whether more exist)."""
+    stmt = (select(DockerLog.id, DockerLog.host_id, DockerLog.container_name,
+                   DockerLog.ts, DockerLog.stream, DockerLog.line)
+            .where(DockerLog.ts >= since))
+    if host_id:
+        stmt = stmt.where(DockerLog.host_id == host_id)
+    if name:
+        stmt = stmt.where(DockerLog.container_name == name)
+    if stream in ("stdout", "stderr"):
+        stmt = stmt.where(DockerLog.stream == stream)
+    if text:
+        stmt = stmt.where(DockerLog.line.ilike(f"%{escape_like(text)}%", escape="\\"))
+    if before is not None:
+        stmt = stmt.where(DockerLog.ts < before)
+    stmt = stmt.order_by(DockerLog.ts.desc(), DockerLog.id.desc()).limit(limit)
+    return list((await db.execute(stmt)).all())
+
+
+async def log_context(db, host_id: str, name: str, ts, n: int) -> tuple[list, list]:
+    """Up to n lines either side of `ts` in one container's log, each oldest first."""
+    cols = (DockerLog.id, DockerLog.ts, DockerLog.stream, DockerLog.line)
+    base = select(*cols).where(DockerLog.host_id == host_id, DockerLog.container_name == name)
+    before = (await db.execute(
+        base.where(DockerLog.ts < ts).order_by(DockerLog.ts.desc(), DockerLog.id.desc()).limit(n)
+    )).all()
+    after = (await db.execute(
+        base.where(DockerLog.ts > ts).order_by(DockerLog.ts, DockerLog.id).limit(n)
+    )).all()
+    return list(reversed(before)), list(after)
+
+
+async def recent_failures_by_container(db, since) -> dict[tuple[str, str], list]:
+    """{(host_id, container_name): [die/oom events since `since`, newest first]}."""
+    rows = (await db.execute(
+        select(DockerEvent)
+        .where(DockerEvent.event.in_(("die", "oom")), DockerEvent.at >= since)
+        .order_by(DockerEvent.at.desc())
+    )).scalars()
+    out: dict[tuple[str, str], list] = {}
+    for e in rows:
+        out.setdefault((e.host_id, e.container_name), []).append(e)
+    return out