feat(mcp): SNMP devices and Prometheus targets: their state, readings and series (#5840)

The snmp plugin registers list_snmp_devices and get_snmp_device; the
prometheus plugin registers list_prometheus_targets and
get_prometheus_target. Both are viewer-level, read what the poller and
scraper stored, and exist only while their plugin is enabled.
get_overview names a device or target whose last poll or scrape failed;
stale, pending and off are left out.

A device's community and v3 keys and a target's token are never
returned, and a password in a target URL is masked.

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

plugins/snmp/__init__.py

@@ -39,3 +39,13 @@ def get_audit_entities() -> dict:
     """Audit rows about a device name it and link to its page."""
     from .models import SnmpDevice
     return {"snmp_device": (SnmpDevice, "/plugins/snmp/devices/{}")}
+
+
+def register_mcp_tools(register) -> None:
+    from .mcp_tools import register_tools
+    register_tools(register)
+
+
+async def mcp_overview(db) -> list[dict]:
+    from .mcp_tools import mcp_overview as findings
+    return await findings(db)

plugins/snmp/mcp_tools.py

@@ -0,0 +1,105 @@
+"""The snmp plugin's MCP tools and its get_overview findings (#5840).
+
+Registered through register_mcp_tools() in __init__.py, so they exist only
+while the plugin is enabled. They read what the poller stored; nothing asks a
+device anything, and a device's community and v3 keys are never returned.
+"""
+from __future__ import annotations
+
+from sqlalchemy import select
+
+from steward.core.metric_series import points
+from steward.mcp._context import mcp_app
+from steward.mcp.tools._shape import age_s, db_session, iso, lookback, now_utc, pick, summarize
+from steward.mcp.tools.overview import finding
+from steward.models.users import UserRole
+
+from .models import SnmpDevice
+from .readings import stored_unit
+from .routes import _latest, shown_readings
+from .service import device_state, readings_for
+
+REACHES = ("down", "stale", "pending", "up")
+_ORDER = {r: i for i, r in enumerate(REACHES)}
+
+
+def _poll_seconds() -> int:
+    return int(mcp_app().config["PLUGINS"]["snmp"].get("poll_interval_seconds", 60))
+
+
+def _device_view(d: SnmpDevice, values: dict, now, poll: int) -> dict:
+    state = device_state(d, poll, now)
+    names = {r.key: r.name for r in readings_for(d)}
+    return {"device_id": d.id, "name": d.name, "address": d.address, "port": d.port, "version": d.version,
+            "host_id": d.host_id, "reach": state.reach, "says": state.says,
+            "polled_at": iso(d.last_polled_at), "ok_at": iso(d.last_ok_at), "ok_age_s": age_s(d.last_ok_at, now),
+            "readings": [{"key": r["key"], "name": r["name"], "value": r["text"], "counter": r["counter"]}
+                         for r in shown_readings(d, values)],
+            "missing": [names.get(k, k) for k in d.missing or []]}
+
+
+async def list_snmp_devices(reach: str = "") -> dict:
+    """The devices Steward polls over SNMP (switches, UPSes, printers, NAS
+    boxes), not answering first.
+
+    reach: "down" (the last poll failed; `says` is why), "stale" (not polled
+      recently: the plugin may be off), "pending" (never polled), "up"; empty
+      for all.
+
+    Each device gives its newest readings in their units (counters as
+    rates), and `missing`: readings it is configured for that the device
+    didn't return. get_snmp_device gives a device's history.
+    """
+    if reach and reach not in REACHES:
+        raise ValueError(f"reach must be one of {', '.join(REACHES)}, or empty for all.")
+    now, poll = now_utc(), _poll_seconds()
+    async with db_session() as db:
+        devices = list((await db.execute(select(SnmpDevice).order_by(SnmpDevice.name))).scalars())
+        values = await _latest(db, [d.name for d in devices])
+    rows = sorted((_device_view(d, values.get(d.name, {}), now, poll) for d in devices),
+                  key=lambda v: (_ORDER[v["reach"]], v["name"].lower()))
+    return {"devices": [r for r in rows if not reach or r["reach"] == reach], "total": len(rows)}
+
+
+async def get_snmp_device(device: str, range: str = "24h") -> dict:
+    """One SNMP device: its state, newest readings, and each reading's
+    history over `range` (min/avg/max/last and ≤60 points, in the unit the
+    reading is stored in: `unit`).
+
+    device: its name or id (list_snmp_devices).
+    range: "1h", "6h", "24h" (default), "7d" or "30d".
+    """
+    since, key = lookback(range)
+    now, poll = now_utc(), _poll_seconds()
+    async with db_session() as db:
+        devices = list((await db.execute(select(SnmpDevice))).scalars())
+        d = pick(device, devices, kind="SNMP device", list_tool="list_snmp_devices")
+        values = (await _latest(db, [d.name])).get(d.name, {})
+        history = {r.key: (stored_unit(r), await points(db, "snmp", d.name, r.key, since))
+                   for r in readings_for(d)}
+    out = _device_view(d, values, now, poll)
+    out["range"] = key
+    out["history"] = {k: {"unit": unit, **summarize(pts)} for k, (unit, pts) in history.items()}
+    return out
+
+
+def device_findings(views: list[dict]) -> list[dict]:
+    """A device whose last poll failed. A stale one is the plugin or poller,
+    not the device, so it is left out."""
+    return [finding("warning", "snmp_device_down", v["name"],
+                    f"SNMP device {v['name']} ({v['address']}) isn't answering: {v['says']}",
+                    since=v["_ok_at"], ids={"device_id": v["device_id"]},
+                    next=f'get_snmp_device(device="{v["name"]}")')
+            for v in views if v["reach"] == "down"]
+
+
+async def mcp_overview(db) -> list[dict]:
+    now, poll = now_utc(), _poll_seconds()
+    devices = list((await db.execute(select(SnmpDevice))).scalars())
+    views = [_device_view(d, {}, now, poll) | {"_ok_at": d.last_ok_at} for d in devices]
+    return device_findings(views)
+
+
+def register_tools(register) -> None:
+    for fn in (list_snmp_devices, get_snmp_device):
+        register(fn, role=UserRole.viewer, read_only=True)