feat(dashboard): phase C richer panels — host time-series graph + cpu sparklines

Milestone 72 phase C — bring the host-view graphs onto the dashboard:
- host_resource_history widget reworked into a real host-view chart: epoch-ms
  linear axis (no Chart.js date adapter), themed like the host-detail charts,
  maintainAspectRatio:false so it fills the resized panel, unique canvas per
  widget instance (wid), and empty states ("pick a host" / "no metrics yet").
  Was previously unusable — it had a broken time axis and no way to choose a host.
- Add a "host" param type: the edit form renders a live dropdown of hosts
  (dashboard routes now pass the host list to the editor); the chosen host_id is
  stored in config and fed to the widget.
- Hosts-overview widget gains a per-row CPU sparkline (last hour) via the shared
  sparkline_svg helper — the host-view at-a-glance trend, on the main widget.

Charts/sparklines render only in the browser, so CI can't exercise them — needs
an operator visual check.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/core/widgets.py

@@ -279,13 +279,20 @@ WIDGET_REGISTRY: dict[str, dict] = {
     },
     "host_resource_history": {
         "key": "host_resource_history",
-        "label": "Host Agent — History",
-        "description": "CPU/memory/disk history for one host",
+        "label": "Host Agent — History Graph",
+        "description": "CPU / memory / disk time-series graph for one host (the host-view chart, on your dashboard)",
         "hx_url": "/plugins/host_agent/widget/history",
-        "detail_url": "/plugins/host_agent/fleet/",
+        "detail_url": "/hosts/",
         "plugin": "host_agent",
         "poll": True,
         "params": [
+            # type "host" → the edit form renders a live dropdown of hosts.
+            {
+                "key": "host_id",
+                "label": "Host",
+                "type": "host",
+                "default": "",
+            },
             {
                 "key": "hours",
                 "label": "Time range",

steward/dashboard/routes.py

@@ -173,7 +173,7 @@ async def _get_panels_data(db, dashboard_id: int) -> tuple:
     result = await db.execute(select(Dashboard).where(Dashboard.id == dashboard_id))
     dash   = result.scalar_one_or_none()
     if dash is None:
-        return None, [], []
+        return None, [], [], []
     widgets     = await _get_widgets(db, dashboard_id)
     plugins_cfg = current_app.config.get("PLUGINS", {})
     available   = get_available_widgets(plugins_cfg)
@@ -182,15 +182,17 @@ async def _get_panels_data(db, dashboard_id: int) -> tuple:
         {"db": w, "defn": WIDGET_REGISTRY[w.widget_key], "title": w.title or WIDGET_REGISTRY[w.widget_key]["label"]}
         for w in widgets if w.widget_key in WIDGET_REGISTRY
     ]
-    return dash, resolved, available
+    # Hosts feed the "host" param dropdown (e.g. the history-graph widget).
+    hosts = list((await db.execute(select(Host).order_by(Host.name))).scalars())
+    return dash, resolved, available, hosts
 
 
 async def _panels_response(dashboard_id: int):
     async with current_app.db_sessionmaker() as db:
-        dash, resolved, addable = await _get_panels_data(db, dashboard_id)
+        dash, resolved, addable, hosts = await _get_panels_data(db, dashboard_id)
     return await render_template(
         "dashboard/_edit_panels.html",
-        dashboard=dash, widgets=resolved, addable=addable,
+        dashboard=dash, widgets=resolved, addable=addable, hosts=hosts,
     )
 
 
@@ -369,12 +371,12 @@ async def edit(dash_id: int):
     user_id   = current_user_id()
     user_role = session.get("user_role", "viewer")
     async with current_app.db_sessionmaker() as db:
-        dash, resolved, addable = await _get_panels_data(db, dash_id)
+        dash, resolved, addable, hosts = await _get_panels_data(db, dash_id)
     if dash is None or not _can_edit(dash, user_id, user_role):
         abort(403)
     return await render_template(
         "dashboard/edit.html",
-        dashboard=dash, widgets=resolved, addable=addable,
+        dashboard=dash, widgets=resolved, addable=addable, hosts=hosts,
     )
 
 

steward/hosts/routes.py

@@ -153,6 +153,36 @@ async def _agent_overview_by_host(db, host_names: list[str]) -> dict[str, dict]:
     return out
 
 
+async def _agent_cpu_sparks_by_host(db, host_names: list[str], hours: int = 1) -> dict[str, str]:
+    """{host_name: inline-SVG cpu sparkline} over the last `hours` (core-safe).
+
+    A tiny at-a-glance trend in each row — the host-view sparkline, on the widget.
+    """
+    from steward.models.metrics import PluginMetric
+    from steward.core.status import sparkline_svg
+    if not host_names:
+        return {}
+    cutoff = datetime.now(timezone.utc) - timedelta(hours=hours)
+    rows = (await db.execute(
+        select(PluginMetric.resource_name, PluginMetric.value, PluginMetric.recorded_at)
+        .where(
+            PluginMetric.source_module == "host_agent",
+            PluginMetric.metric_name == "cpu_pct",
+            PluginMetric.resource_name.in_(host_names),
+            PluginMetric.recorded_at >= cutoff,
+        )
+        .order_by(PluginMetric.recorded_at)
+    )).all()
+    by_host: dict[str, list[float]] = {}
+    for r in rows:
+        by_host.setdefault(r.resource_name, []).append(r.value)
+    # Amber line to read as "CPU"; only draw when there are a couple of points.
+    return {
+        name: sparkline_svg(vals[-40:], width=64, height=18, stroke="#c8a840")
+        for name, vals in by_host.items() if len(vals) >= 2
+    }
+
+
 @hosts_bp.get("/overview/widget")
 @require_role(UserRole.viewer)
 async def overview_widget():
@@ -180,12 +210,14 @@ async def overview_widget():
                 & (DnsResult.resolved_at == latest_dns_subq.c.max_at),
             ))).scalars()}
         uptime = await _compute_uptime(db)
-        agent = await _agent_overview_by_host(db, [h.name for h in hosts])
+        host_names = [h.name for h in hosts]
+        agent = await _agent_overview_by_host(db, host_names)
+        cpu_sparks = await _agent_cpu_sparks_by_host(db, host_names)
 
     return await render_template(
         "hosts/overview_widget.html",
         hosts=hosts, latest_pings=latest_pings, latest_dns=latest_dns,
-        uptime=uptime, agent=agent,
+        uptime=uptime, agent=agent, cpu_sparks=cpu_sparks,
     )
 
 

steward/templates/dashboard/_edit_panels.html

@@ -92,6 +92,16 @@
                   </option>
                   {% endfor %}
                 </select>
+                {% elif p.type == "host" %}
+                <select name="param_{{ p.key }}" required
+                        style="width:100%;padding:0.32rem 0.6rem;background:var(--bg);
+                               border:1px solid var(--border-mid);border-radius:4px;
+                               color:var(--text);font-size:0.85rem;">
+                  <option value="">— select a host —</option>
+                  {% for h in hosts %}
+                  <option value="{{ h.id }}">{{ h.name }}</option>
+                  {% endfor %}
+                </select>
                 {% endif %}
               </div>
               {% endfor %}

steward/templates/hosts/overview_widget.html

@@ -17,6 +17,8 @@
     {% else %}
     <span title="{{ host.name }}" style="{{ name_style }}">{{ host.name }}</span>
     {% endif %}
+    {% set spark = cpu_sparks.get(host.name) %}
+    {% if spark %}<span title="CPU — last hour" style="flex-shrink:0;line-height:0;opacity:0.85;">{{ spark | safe }}</span>{% endif %}
     <span style="display:flex;gap:0.75rem;font-variant-numeric:tabular-nums;color:var(--text-muted);font-size:0.75rem;flex-shrink:0;">
       {# Monitors #}
       {% if host.ping_enabled and ping and ping.response_time_ms is not none %}