studio: skip training status/metrics polling when idle (#4988)

* fix(studio): skip training status/metrics polling when idle

Add an early return in the status and metrics setInterval callbacks when
the runtime store reports phase === "idle" and hasHydrated is true.
Previously these polls fired unconditionally every 3s/5s, generating
unnecessary network traffic and console errors when no training was
running.

* fix(studio): reduce idle polling to 30s instead of stopping entirely

Review feedback (PR #4988): completely stopping polling when idle risks
permanent UI desync if hydration fails, and misses out-of-band state
changes from other clients. Add a 30s background poll that only fires
when idle to recover gracefully.

* fix: harden idle status polling around hydration and runtime reset

---------

Co-authored-by: AdamPlatin123 <AdamPlatin123@users.noreply.github.com>
Co-authored-by: Lee Jackson <130007945+Imagineer99@users.noreply.github.com>
Co-authored-by: imagineer99 <samleejackson0@gmail.com>

studio/frontend/src/features/training/hooks/use-training-runtime-lifecycle.ts

@@ -14,6 +14,7 @@ import type { TrainingRuntimeStore } from "../types/runtime";
 
 const STATUS_POLL_INTERVAL_MS = 3000;
 const METRICS_POLL_INTERVAL_MS = 5000;
+const IDLE_POLL_INTERVAL_MS = 30000;
 const STREAM_RECONNECT_DELAY_MS = 1500;
 
 function shouldUseLiveSync(state: TrainingRuntimeStore): boolean {
@@ -164,21 +165,37 @@ export function useTrainingRuntimeLifecycle(): void {
 
     void hydrate();
 
+    const isIdle = () => {
+      const s = runtimeStore.getState();
+      return s.phase === "idle" && !s.isTrainingRunning;
+    };
+
     const statusTimer = setInterval(() => {
+      const s = runtimeStore.getState();
+      if (isIdle() && s.hasHydrated) return;
       void pollStatus();
     }, STATUS_POLL_INTERVAL_MS);
 
     const metricsTimer = setInterval(() => {
-      const state = runtimeStore.getState();
-      if (shouldUseLiveSync(state) || state.currentStep > 0) {
+      if (isIdle()) return;
+      const s = runtimeStore.getState();
+      if (shouldUseLiveSync(s) || s.currentStep > 0) {
         void pollMetrics();
       }
     }, METRICS_POLL_INTERVAL_MS);
 
+    // Low-frequency background poll to recover from failed hydration or detect
+    // out-of-band state changes (e.g. training started from another client).
+    const idleTimer = setInterval(() => {
+      if (!isIdle()) return;
+      void pollStatus();
+    }, IDLE_POLL_INTERVAL_MS);
+
     return () => {
       disposed = true;
       clearInterval(statusTimer);
       clearInterval(metricsTimer);
+      clearInterval(idleTimer);
       stopStream();
     };
   }, []);

studio/frontend/src/features/training/stores/training-runtime-store.ts

@@ -125,6 +125,7 @@ export const useTrainingRuntimeStore = create<TrainingRuntimeStore>()((set) => (
   resetRuntime: () =>
     set((state) => ({
       ...initialState,
+      hasHydrated: state.hasHydrated,
       lossHistory: [],
       lrHistory: [],
       gradNormHistory: [],