P2R-02 slice 5: dashboard row Run-now uses covering schedule

Replace the placeholder 'Open →' link with a per-host Run-now
decision computed server-side once per render:

* If the host has exactly one enabled schedule whose source-group
  set covers every group on the host → primary 'Run all groups'
  button (HX-POST to that schedule's /run endpoint, fires every
  backup the host knows about in one click).
* Otherwise (zero matches, multiple matches, or any ambiguity) →
  ghost 'Open →' link to /hosts/{id}/sources, where the operator
  picks per-group from the source-group rows.

dashboardPage.Hosts moves from []store.Host to []dashboardHostRow
to carry the precomputed RunAllScheduleID; host_row.html now reads
.Host.* and .RunAllScheduleID. Two extra store calls per host on
dashboard render — fine at fleet sizes we care about; if we ever
need to support thousands of hosts we'll batch these queries.

internal/server/http/ui_handlers.go

@@ -103,11 +103,64 @@ func (s *Server) version() string {
 
 // dashboardPage is the data the dashboard template renders against.
 type dashboardPage struct {
-	Hosts     []store.Host
+	Hosts     []dashboardHostRow
 	HostCount int
 	Summary   store.FleetSummary
 }
 
+// dashboardHostRow carries a host plus the per-row Run-now decision
+// the host_row partial needs. The decision is computed server-side
+// once per render rather than recomputed in the template.
+type dashboardHostRow struct {
+	Host store.Host
+	// RunAllScheduleID is the ID of the single schedule that covers
+	// every source group on the host. Empty when zero or 2+ schedules
+	// match — in that case the row shows "Open →" instead of a Run-now
+	// button (the operator picks per-group from the host detail).
+	RunAllScheduleID string
+}
+
+// pickRunAllSchedule returns the ID of the single schedule whose
+// source-group set ⊇ every source group on the host. Returns "" when
+// zero or 2+ such "covering" schedules exist (operator-disambiguation
+// belongs on the host detail, not the dashboard one-click).
+func pickRunAllSchedule(scheds []store.Schedule, groups []store.SourceGroup) string {
+	if len(groups) == 0 || len(scheds) == 0 {
+		return ""
+	}
+	groupIDs := make(map[string]struct{}, len(groups))
+	for _, g := range groups {
+		groupIDs[g.ID] = struct{}{}
+	}
+	matched := ""
+	for _, sc := range scheds {
+		if !sc.Enabled {
+			continue
+		}
+		// Treat sc.SourceGroupIDs as a set; check it covers every group.
+		got := make(map[string]struct{}, len(sc.SourceGroupIDs))
+		for _, gid := range sc.SourceGroupIDs {
+			got[gid] = struct{}{}
+		}
+		covers := true
+		for gid := range groupIDs {
+			if _, ok := got[gid]; !ok {
+				covers = false
+				break
+			}
+		}
+		if !covers {
+			continue
+		}
+		if matched != "" {
+			// Two distinct covering schedules — ambiguous, bail out.
+			return ""
+		}
+		matched = sc.ID
+	}
+	return matched
+}
+
 // handleUIDashboard is the root page. Auth-gated; falls through to
 // /login if there is no session.
 func (s *Server) handleUIDashboard(w stdhttp.ResponseWriter, r *stdhttp.Request) {
@@ -129,10 +182,28 @@ func (s *Server) handleUIDashboard(w stdhttp.ResponseWriter, r *stdhttp.Request)
 		return
 	}
 
+	// Per-host: pick the single covering schedule (if any) so the row
+	// can render a one-click Run-now where it's unambiguous. Two store
+	// calls per host — fine at fleet sizes we care about.
+	rows := make([]dashboardHostRow, 0, len(hosts))
+	for _, h := range hosts {
+		row := dashboardHostRow{Host: h}
+		groups, gerr := s.deps.Store.ListSourceGroupsByHost(r.Context(), h.ID)
+		if gerr != nil {
+			slog.Warn("ui dashboard: list source groups", "host_id", h.ID, "err", gerr)
+		}
+		scheds, serr := s.deps.Store.ListSchedulesByHost(r.Context(), h.ID)
+		if serr != nil {
+			slog.Warn("ui dashboard: list schedules", "host_id", h.ID, "err", serr)
+		}
+		row.RunAllScheduleID = pickRunAllSchedule(scheds, groups)
+		rows = append(rows, row)
+	}
+
 	view := s.baseView(u, "dashboard")
 	view.OpenAlerts = summary.OpenAlerts
 	view.Page = dashboardPage{
-		Hosts:     hosts,
+		Hosts:     rows,
 		HostCount: len(hosts),
 		Summary:   summary,
 	}