Add 10-min GPU idle-shutdown; make Preview/Code toggle a real button

The simulated NVIDIA GPU badge now sleeps after 10 minutes without a
Run Test, mirroring real rented-GPU cost behavior; the next run pays
an honest, logged cold-start delay to wake it. Also replaced the
easy-to-miss vertical edge tab with a bold fixed pill button
(bottom-right) for Preview/Code, since the original was overlapping
other text and going unnoticed.

src/app/testbench/Testbench.tsx

@@ -35,6 +35,8 @@ type SessionRun = {
   log: string[];
 };
 
+const GPU_IDLE_TIMEOUT_MS = 10 * 60 * 1000;
+
 export default function Testbench() {
   const [targets, setTargets] = useState<Target[] | null>(null);
   const [targetsError, setTargetsError] = useState<string | null>(null);
@@ -69,6 +71,26 @@ export default function Testbench() {
   // effect of every individual run.
   const [sessionRuns, setSessionRuns] = useState<SessionRun[]>([]);
 
+  // Idle-shutdown for the simulated GPU: mirrors real rented-GPU behavior —
+  // no Run Test activity for GPU_IDLE_TIMEOUT_MS puts it to sleep so it isn't
+  // "billing" while unused; the next run pays a short cold-start cost to wake
+  // it back up instead of silently staying "on" forever.
+  const [gpuAsleep, setGpuAsleep] = useState(false);
+  const gpuIdleTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  function resetGpuIdleTimer() {
+    if (gpuIdleTimerRef.current) clearTimeout(gpuIdleTimerRef.current);
+    gpuIdleTimerRef.current = setTimeout(() => setGpuAsleep(true), GPU_IDLE_TIMEOUT_MS);
+  }
+
+  useEffect(() => {
+    resetGpuIdleTimer();
+    return () => {
+      if (gpuIdleTimerRef.current) clearTimeout(gpuIdleTimerRef.current);
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
   useEffect(() => {
     fetch("/api/testbench")
       .then(async (res) => {
@@ -108,6 +130,7 @@ export default function Testbench() {
     if (tickRef.current) clearInterval(tickRef.current);
     if (lockTimeoutRef.current) clearTimeout(lockTimeoutRef.current);
 
+    resetGpuIdleTimer();
     setTab("console");
 
     // Re-verify the lock right at the boundary where nodes leave the grid.
@@ -139,18 +162,43 @@ export default function Testbench() {
     const script = buildSimulatedRunScript(berylPipeline, label);
 
     const introLine = `Artifact lock verified — sha256:${fresh.checksum.slice(0, 16)}… · ${fresh.byteSize}B · ${fresh.loc} LOC · ${fresh.nodeCount} nodes. Checked out from the front for this run.`;
-    setLog([{ atMs: 0, level: "ok", text: introLine }]);
+
+    // If the GPU went to sleep from inactivity, waking it back up costs a
+    // short, honestly-logged cold-start delay before the run actually begins.
+    const wasAsleep = gpuAsleep;
+    const preamble: SandboxLogLine[] = [];
+    let preambleT = 0;
+    if (wasAsleep) {
+      preamble.push({
+        atMs: preambleT,
+        level: "warn",
+        text: "GPU was asleep (idle >10min, shut off to avoid wasting money) — cold-starting...",
+      });
+      preambleT += 1200;
+      preamble.push({ atMs: preambleT, level: "ok", text: "NVIDIA GPU allocation restored (simulated)." });
+      preambleT += 700;
+    }
+    preamble.push({ atMs: preambleT, level: "ok", text: introLine });
+
+    setLog([]);
     setElapsedMs(0);
     setRunState("running");
     setLockStatus("checked-out");
+    if (wasAsleep) setGpuAsleep(false);
 
     const start = Date.now();
     tickRef.current = setInterval(() => setElapsedMs(Date.now() - start), 200);
 
+    preamble.forEach((line) => {
+      const timer = setTimeout(() => setLog((prev) => [...prev, line]), line.atMs);
+      timers.current.push(timer);
+    });
+
+    const scriptOffset = preambleT;
     script.forEach((line) => {
       const timer = setTimeout(() => {
         setLog((prev) => [...prev, line]);
-      }, line.atMs);
+      }, line.atMs + scriptOffset);
       timers.current.push(timer);
     });
 
@@ -166,7 +214,7 @@ export default function Testbench() {
       ]);
     }, DEFAULT_LOCK_TIMEOUT_MS);
 
-    const finishAt = script[script.length - 1]?.atMs ?? 0;
+    const finishAt = (script[script.length - 1]?.atMs ?? 0) + scriptOffset;
     const finishTimer = setTimeout(async () => {
       setRunState("done");
       if (tickRef.current) clearInterval(tickRef.current);
@@ -265,11 +313,14 @@ export default function Testbench() {
     <div className="flex-1 flex flex-col h-[calc(100dvh-var(--topnav-h))] relative">
       <button
         onClick={toggleCodeView}
-        className="fixed right-0 top-1/2 -translate-y-1/2 z-30 flex flex-col items-center gap-1.5 px-2 py-3 rounded-l-lg border border-r-0 border-[var(--panel-border)] glass-panel text-[10px] font-semibold tracking-wide text-[var(--muted)] hover:text-white transition"
-        style={{ writingMode: "vertical-rl" }}
+        className={`fixed right-5 bottom-6 z-30 flex items-center gap-2 px-4 py-2.5 rounded-full border-2 shadow-lg text-xs font-bold tracking-wide transition hover:scale-105 ${
+          codeView
+            ? "bg-[var(--accent-teal)] border-[var(--accent-teal)] text-black"
+            : "bg-[var(--panel)] border-[var(--gold)] text-[var(--gold-bright)]"
+        }`}
         title={codeView ? "Switch to Preview" : "Switch to Code — real source from the reference targets"}
       >
-        {codeView ? <Eye size={12} /> : <Code2 size={12} />}
+        {codeView ? <Eye size={15} /> : <Code2 size={15} />}
         {codeView ? "PREVIEW" : "CODE"}
       </button>
 
@@ -284,8 +335,15 @@ export default function Testbench() {
           </span>
         </div>
         <div className="ml-auto flex items-center gap-2 shrink-0">
-          <span className="flex items-center gap-1.5 text-xs px-3 py-1.5 rounded-full border border-[var(--accent-teal)]/40 text-[var(--accent-teal)]">
-            <Cpu size={12} /> NVIDIA GPU · simulated
+          <span
+            className={`flex items-center gap-1.5 text-xs px-3 py-1.5 rounded-full border transition ${
+              gpuAsleep
+                ? "border-[var(--panel-border)] text-[var(--muted)]"
+                : "border-[var(--accent-teal)]/40 text-[var(--accent-teal)]"
+            }`}
+            title={gpuAsleep ? `Idle >${GPU_IDLE_TIMEOUT_MS / 60000}min — shut off to avoid wasting money. Run Test to wake it.` : undefined}
+          >
+            <Cpu size={12} /> NVIDIA GPU · {gpuAsleep ? "sleeping (idle)" : "simulated"}
           </span>
         </div>
       </header>