Top wears the skin; the refresh rate reaches every machine; bug bash 4

The process table's columns fit the box they are in, the rate control saves, curves are
timed on the viewer's clock and keep to the stride, the power icon is drawn, and a young
history draws in from the right instead of being stretched.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/api/server.go

@@ -98,6 +98,24 @@ func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *me
 	if histSec > 0 {
 		col.SetWindow(time.Duration(histSec) * time.Second)
 	}
+	// The sampler follows the console's refresh rate. A machine remembers what it was last told;
+	// the hub reads the rate from the saved UI prefs and tells everyone again, because a node
+	// that restarted, or was added since, would otherwise sample at its default until somebody
+	// happened to open its Dashboard.
+	var samplerMs int
+	var uiRaw json.RawMessage
+	st.View(func(x *store.State) { samplerMs, uiRaw = x.SamplerMs, x.UI })
+	if samplerMs > 0 {
+		col.SetInterval(time.Duration(samplerMs) * time.Millisecond)
+	}
+	if nm != nil {
+		var ui struct {
+			RefreshMs float64 `json:"refreshMs"`
+		}
+		if json.Unmarshal(uiRaw, &ui) == nil && ui.RefreshMs >= 100 {
+			go s.setSampler(int(ui.RefreshMs), true)
+		}
+	}
 	// A node that restarted, or was added since, has its own idea of the window: tell them all.
 	if histSec > 0 && nm != nil {
 		go s.pushHistoryWindow(histSec)
@@ -223,6 +241,8 @@ func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *me
 		r.URL.Path = strings.TrimPrefix(r.URL.Path, "/api")
 		pprof.Index(w, r)
 	}))
+	m.HandleFunc("GET /api/prefs/sampler", s.auth(s.getSampler))
+	m.HandleFunc("PUT /api/prefs/sampler", s.auth(s.putSampler))
 	m.HandleFunc("GET /api/prefs/history", s.auth(s.getHistoryWindow))
 	m.HandleFunc("PUT /api/prefs/history", s.auth(s.putHistoryWindow))
 	m.HandleFunc("GET /api/prefs/dashboard", s.auth(s.getDashPrefs))
@@ -1895,9 +1915,62 @@ func (s *Server) putUIPrefs(w http.ResponseWriter, r *http.Request) {
 		jsonErr(w, 500, err.Error())
 		return
 	}
+	if p.RefreshMs != nil { // the refresh rate is also how often every machine samples
+		go s.setSampler(int(*p.RefreshMs), true)
+	}
 	w.WriteHeader(204)
 }
 
+// ---- how often the machine samples ----
+//
+// One rate for the fleet, the console's refresh rate: set in Settings (or the Top tab), saved
+// with the UI prefs on the hub, and passed by the hub to every machine. Before this the
+// sampler was told only by an open Dashboard page, so a machine whose Dashboard nobody had
+// opened since the rate changed kept sampling at the old one, and every other page of it —
+// Top, Processes, Disks, widgets — "ignored" the setting.
+
+// setSampler applies a rate here and, from a hub, everywhere. The collector's own limits are
+// 100 ms to 10 s; a slower console rate samples at 10 s.
+func (s *Server) setSampler(ms int, fanOut bool) {
+	lo, hi := int(metrics.MinInterval.Milliseconds()), int(metrics.MaxInterval.Milliseconds())
+	if ms < lo {
+		ms = lo
+	}
+	if ms > hi {
+		ms = hi
+	}
+	s.metrics.SetInterval(time.Duration(ms) * time.Millisecond)
+	_ = s.store.Update(func(st *store.State) { st.SamplerMs = ms })
+	if !fanOut || s.nodes == nil {
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	defer cancel()
+	body, _ := json.Marshal(map[string]int{"ms": ms})
+	hdr := http.Header{"X-Hamlab-From-Hub": []string{"1"}, "Content-Type": []string{"application/json"}}
+	for _, name := range s.nodes.Names() {
+		if code, _, err := s.nodes.Do(ctx, name, "PUT", "/api/prefs/sampler", body, hdr); err != nil || code >= 400 {
+			log.Printf("sampler: %s did not take %d ms (%d %v)", name, ms, code, err)
+		}
+	}
+}
+
+func (s *Server) getSampler(w http.ResponseWriter, _ *http.Request) {
+	jsonOK(w, 200, map[string]any{"ms": s.metrics.Interval().Milliseconds(), "min_ms": metrics.MinInterval.Milliseconds(), "max_ms": metrics.MaxInterval.Milliseconds()})
+}
+
+func (s *Server) putSampler(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		Ms int `json:"ms"`
+	}
+	if json.NewDecoder(io.LimitReader(r.Body, 4096)).Decode(&body) != nil || body.Ms < 100 || body.Ms > 60000 {
+		jsonErr(w, 400, "expected {\"ms\": 100…60000}")
+		return
+	}
+	s.setSampler(body.Ms, r.Header.Get("X-Hamlab-From-Hub") == "")
+	s.getSampler(w, r)
+}
+
 // ---- how far back the graphs reach ----
 //
 // One window for the whole fleet: the hub keeps it and pushes it to every machine, so a