feat(snmp): surface SNMP device readings on the matching host page

SNMP devices are config-defined by IP/hostname, not Steward Host records, so
they had no presence on a host's page. Map them by address and embed a fragment
(mirrors the Docker per-host fragment).

- _devices_for_host(devices_cfg, address, name): case-insensitive match of a
  device's configured host to the Steward host's address or name (tolerates
  non-dict / host-less entries).
- Route /plugins/snmp/host/<id>: renders the matched device(s) + latest readings,
  or nothing when none map (so hosts without SNMP carry no empty card).
- snmp/host_panel.html: per-device card (name · address · reachability) with a
  readings grid (K/M scaling) and a History link to the full device page.
- hosts/detail.html embeds it after the Docker fragment, gated on snmp enabled.
- Unit test for the matching helper (by address, by name, no-match, blank).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Jg27rgypiW2efULXJDtMC

plugins/snmp/routes.py

@@ -93,6 +93,48 @@ async def index():
                                  poll_interval=poll_interval)
 
 
+def _devices_for_host(devices_cfg: list, address: str | None, name: str | None) -> list[dict]:
+    """SNMP devices whose configured `host` matches a Steward host's address or
+    name (case-insensitive). SNMP devices are config-defined by IP/hostname, so
+    this is how they map onto a host's page."""
+    keys = {(address or "").strip().lower(), (name or "").strip().lower()}
+    keys.discard("")
+    return [
+        d for d in devices_cfg
+        if isinstance(d, dict) and str(d.get("host", "")).strip().lower() in keys
+    ]
+
+
+@snmp_bp.get("/host/<host_id>")
+@require_role(UserRole.viewer)
+async def host_panel(host_id: str):
+    """Per-host SNMP fragment for the Hosts hub. Surfaces any configured SNMP
+    device that maps to this host (by address or name) with its latest readings.
+    Renders nothing when no device maps, so hosts without SNMP carry no empty card.
+    """
+    from steward.models.hosts import Host
+
+    devices_cfg: list[dict] = current_app.config["PLUGINS"]["snmp"].get("devices", [])
+    async with current_app.db_sessionmaker() as db:
+        host = (await db.execute(
+            select(Host).where(Host.id == host_id))).scalar_one_or_none()
+        if host is None:
+            return ""
+        matched = _devices_for_host(devices_cfg, host.address, host.name)
+        if not matched:
+            return ""
+        names = [d.get("name") or d.get("host", "?") for d in matched]
+        latest = await _latest_readings(db, names)
+
+    devices = [{
+        "name": d.get("name") or d.get("host", "?"),
+        "host": d.get("host", ""),
+        "oids": d.get("oids", []),
+        "readings": latest.get(d.get("name") or d.get("host", "?"), {}),
+    } for d in matched]
+    return await render_template("snmp/host_panel.html", devices=devices)
+
+
 @snmp_bp.get("/widget")
 @require_role(UserRole.viewer)
 async def widget():

plugins/snmp/templates/snmp/host_panel.html

@@ -0,0 +1,47 @@
+{# Per-host SNMP fragment — embedded on the Hosts hub via HTMX. Self-contained.
+   Shows the SNMP device(s) whose address maps to this host + latest readings. #}
+<div class="card">
+  <div style="display:flex;align-items:baseline;justify-content:space-between;margin-bottom:0.6rem;gap:1rem;flex-wrap:wrap;">
+    <h3 class="section-title" style="margin-bottom:0;">SNMP</h3>
+    <a href="/plugins/snmp/" style="font-size:0.8rem;color:var(--text-muted);">All devices →</a>
+  </div>
+
+  {% for device in devices %}
+  <div style="{% if not loop.last %}margin-bottom:1rem;{% endif %}">
+    <div style="display:flex;align-items:center;gap:0.6rem;margin-bottom:0.5rem;flex-wrap:wrap;">
+      <span style="font-weight:600;font-size:0.92rem;">{{ device.name }}</span>
+      <span style="font-size:0.78rem;color:var(--text-dim);font-family:ui-monospace,monospace;">{{ device.host }}</span>
+      {% if device.readings %}
+      <span style="font-size:0.74rem;color:var(--green);">&#9679; reachable</span>
+      {% else %}
+      <span style="font-size:0.74rem;color:var(--text-dim);">&#9675; no data yet</span>
+      {% endif %}
+      <a href="/plugins/snmp/device/{{ device.name }}" class="btn btn-ghost btn-sm"
+         style="margin-left:auto;font-size:0.76rem;padding:0.15rem 0.55rem;">History</a>
+    </div>
+
+    {% if device.readings %}
+    <div style="display:grid;grid-template-columns:repeat(auto-fill,minmax(150px,1fr));gap:0.5rem;">
+      {% for oid_cfg in device.oids %}
+      {% set label = oid_cfg.label if oid_cfg.label else oid_cfg.oid %}
+      {% set val = device.readings.get(label) %}
+      <div style="background:var(--bg-elevated);border-radius:5px;padding:0.5rem 0.7rem;border:1px solid var(--border);">
+        <div style="font-size:0.68rem;color:var(--text-dim);margin-bottom:0.2rem;font-family:ui-monospace,monospace;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;">{{ label }}</div>
+        {% if val is not none %}
+        <div style="font-size:1rem;font-weight:600;font-variant-numeric:tabular-nums;">
+          {% if val >= 1000000 %}{{ "%.2f"|format(val / 1000000) }}<span style="font-size:0.72rem;color:var(--text-muted);">M</span>
+          {% elif val >= 1000 %}{{ "%.1f"|format(val / 1000) }}<span style="font-size:0.72rem;color:var(--text-muted);">K</span>
+          {% else %}{{ "%.4g"|format(val) }}{% endif %}
+        </div>
+        {% else %}
+        <div style="font-size:0.85rem;color:var(--text-dim);">—</div>
+        {% endif %}
+      </div>
+      {% endfor %}
+    </div>
+    {% else %}
+    <p style="font-size:0.8rem;color:var(--text-dim);margin:0;">No readings yet — waiting for the next poll.</p>
+    {% endif %}
+  </div>
+  {% endfor %}
+</div>

steward/templates/hosts/detail.html

@@ -224,6 +224,11 @@
 <div hx-get="/plugins/docker/host/{{ host.id }}" hx-trigger="load" hx-swap="innerHTML"></div>
 {% endif %}
 
+{# ── SNMP (renders nothing unless a configured SNMP device maps to this host) ── #}
+{% if "snmp" in enabled_plugins %}
+<div hx-get="/plugins/snmp/host/{{ host.id }}" hx-trigger="load" hx-swap="innerHTML"></div>
+{% endif %}
+
 {{ toggle_script() }}
 <script>var _mt=document.getElementById('mtype'); if(_mt) mtoggle(_mt.value);</script>
 {% endblock %}

tests/plugins/snmp/test_host_match.py

@@ -0,0 +1,29 @@
+"""Unit tests for mapping config-defined SNMP devices onto a Steward host."""
+from plugins.snmp.routes import _devices_for_host
+
+_CFG = [
+    {"name": "core-switch", "host": "192.168.1.1"},
+    {"name": "ups", "host": "192.168.1.10"},
+    {"name": "by-name", "host": "edge-router"},
+    "not-a-dict",                     # tolerated, skipped
+    {"name": "no-host"},              # no host → never matches
+]
+
+
+def test_matches_by_address():
+    out = _devices_for_host(_CFG, "192.168.1.1", "somehost")
+    assert [d["name"] for d in out] == ["core-switch"]
+
+
+def test_matches_by_name_case_insensitive():
+    out = _devices_for_host(_CFG, "10.0.0.9", "Edge-Router")
+    assert [d["name"] for d in out] == ["by-name"]
+
+
+def test_no_match_returns_empty():
+    assert _devices_for_host(_CFG, "10.0.0.1", "nope") == []
+
+
+def test_blank_address_and_name_match_nothing():
+    # A host with no address/name must not match a device with a blank host.
+    assert _devices_for_host(_CFG, "", None) == []