feat(hosts): the Hosts list labels its figures and says how long; SLA tab gone; one place to add a host (#5279–#5283)

Hosts list:
- CPU and Memory are their own labelled columns (#5279); a silent
  agent's last readings are greyed, and Status says "agent silent for 7m".
- One uptime figure, 30 days, with 24h and 7d on hover. The SLA tab
  (/hosts/uptime) repeated it and is removed (#5280; one home per fact).
- Status is a word with how long ("Down for 12m"); host_status now carries
  down_since. Edit and Delete live on the host's page only (#5281).
- Figures are right-aligned with tabular digits (.table .num), not a
  monospace face.

Agent fleet (#5282): its add-host form is gone, so hosts are added only on
Hosts -> Add host. That form was also the only way to get a token for a
manual curl install, so that moves to the host's Agent card as "Install
manually" (POST /fleet/<host_id>/register), shown on the fleet page as
before. "Delete" there reads "Unregister".

Add host (#5283): laid out like the add-monitor form; a name clash comes
back inline with what was typed instead of a bare text 400; the address
is optional, as the host page already allowed.

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

steward/hosts/routes.py

@@ -112,7 +112,8 @@ async def create_host():
             try:
                 await host_svc.check_name_free(db, host.name)
             except ValueError as exc:
-                return str(exc), 400
+                return await render_template("hosts/form.html", host=None, values=form,
+                                             error=str(exc)), 400
             db.add(host)
     await log_audit(current_app, session.get("user_id"), session.get("username", ""),
                     "host.created", entity_type="host", entity_id=host.name,
@@ -150,7 +151,8 @@ async def update_host(host_id: str):
                 try:
                     await host_svc.check_name_free(db, name, exclude_id=host.id)
                 except ValueError as exc:
-                    return str(exc), 400
+                    return await render_template("hosts/form.html", host=host, values=form,
+                                                 error=str(exc)), 400
             host.name = name
             host.address = form["address"].strip()
             # Agent and container metrics, and the rules and windows on them,
@@ -296,13 +298,3 @@ async def delete_host(host_id: str):
         await log_audit(current_app, session.get("user_id"), session.get("username", ""),
                         "host.deleted", entity_type="host", entity_id=host_name)
     return redirect(url_for("hosts.list_hosts"))
-
-
-@hosts_bp.get("/uptime")
-@require_role(UserRole.viewer)
-async def uptime_page():
-    async with current_app.db_sessionmaker() as db:
-        result = await db.execute(select(Host).order_by(Host.name))
-        uptime = await host_svc.compute_uptime(db)
-        hosts = host_svc.worst_uptime_first(result.scalars().all(), uptime)
-    return await render_template("hosts/uptime.html", hosts=hosts, uptime=uptime)

steward/hosts/service.py

@@ -88,8 +88,10 @@ async def host_status(db, host_ids: list[str]) -> dict[str, dict]:
     """Per-host status rollup from the latest result of each linked monitor.
 
     {host_id: {"state": "up"|"down"|"pending", "latency_ms": float|None,
-               "count": int}}. State is down if ANY linked monitor's latest
-    result is down (worst-case), up if at least one is up, else pending.
+               "count": int, "down_since": datetime|None}}. State is down if
+    ANY linked monitor's latest result is down (worst-case), up if at least
+    one is up, else pending. down_since is when the longest-down of its down
+    monitors went down.
     """
     if not host_ids:
         return {}
@@ -98,32 +100,29 @@ async def host_status(db, host_ids: list[str]) -> dict[str, dict]:
         .where(Monitor.host_id.in_(host_ids), Monitor.enabled.is_(True))
     )).all()
     latest = await _last_n_results(db, [m.id for m in monitors], n=1)
-    rows = [(latest[mid][-1], host_id) for mid, host_id in monitors if latest.get(mid)]
+    rows = [(latest[mid][-1], host_id, mid) for mid, host_id in monitors if latest.get(mid)]
     out: dict[str, dict] = {}
-    for res, host_id in rows:
-        d = out.setdefault(host_id, {"state": "pending", "latency_ms": None, "count": 0})
+    down: dict[str, list[str]] = {}
+    for res, host_id, mid in rows:
+        d = out.setdefault(host_id, {"state": "pending", "latency_ms": None, "count": 0,
+                                     "down_since": None})
         d["count"] += 1
         if not res.is_up:
             d["state"] = "down"
+            down.setdefault(host_id, []).append(mid)
         elif d["state"] != "down":
             d["state"] = "up"
         if res.is_up and res.response_ms is not None:
             d["latency_ms"] = (res.response_ms if d["latency_ms"] is None
                                else min(d["latency_ms"], res.response_ms))
+    if down:
+        from steward.monitors.service import down_since
+        for host_id, mids in down.items():
+            starts = [t for t in [await down_since(db, mid) for mid in mids] if t]
+            out[host_id]["down_since"] = min(starts) if starts else None
     return out
 
 
-def worst_uptime_first(hosts, uptime: dict) -> list:
-    """Hosts by their 24h uptime, worst first, then 7d and 30d to break ties;
-    hosts with no uptime yet (no monitors) last, by name."""
-    def key(h):
-        u = uptime.get(h.id) or {}
-        windows = [u.get(w) for w in ("24h", "7d", "30d")]
-        known = [w for w in windows if w is not None]
-        return (not known, *[101.0 if w is None else w for w in windows], h.name.lower())
-    return sorted(hosts, key=key)
-
-
 def host_rank(status: dict | None, agent: dict | None) -> int:
     """Where a host sorts in the Hosts list: a down monitor first, then an
     agent gone quiet, then monitors not yet checked, then the healthy; a host