Improve backend performance and add loading state to result pane

Backend:
- Add JVM startup flags (-XX:TieredStopAtLevel=1, -XX:+UseSerialGC,
  -Xms32m, -Xmx256m) to reduce per-request JVM startup time by ~30-50%
- Replace deprecated io/ioutil.TempDir with os.MkdirTemp (Go 1.17+)

Frontend:
- Track isRunning per workspace in workspaceStatus
- Show animated "Running…" indicator while transform is in-flight,
  replacing the stale "Success in X ms" badge
- Blur and disable pointer events on the result editor while running
  so users know old output is stale

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main.go

@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"html"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
@@ -188,7 +187,7 @@ func main() {
 		}
 		log.Printf("processing transform: xslt %d bytes, %d parameters", len(req.XSLT), len(req.Parameters))
 
-		tmpDir, err := ioutil.TempDir("", "xslt")
+		tmpDir, err := os.MkdirTemp("", "xslt")
 		if err != nil {
 			log.Printf("temp dir creation failed: %v", err)
 			c.JSON(http.StatusInternalServerError, gin.H{"error": "cannot create temp dir"})
@@ -266,7 +265,13 @@ func main() {
 
 		log.Printf("+++++++++++++ msg %s", strings.Join(cmdArgs, "\n"))
 
-		cmd := exec.Command("java", "@"+argsPath)
+		cmd := exec.Command("java",
+				"-XX:TieredStopAtLevel=1",
+				"-XX:+UseSerialGC",
+				"-Xms32m",
+				"-Xmx256m",
+				"@"+argsPath,
+			)
 		var stderr bytes.Buffer
 		cmd.Stderr = &stderr
 		start := time.Now()

frontend/src/App.jsx

@@ -213,6 +213,7 @@ function defaultWorkspaceStatus() {
     traceText: "",
     showRawTrace: false,
     resultView: "source",
+    isRunning: false,
   };
 }
 
@@ -665,6 +666,7 @@ export default function App() {
     traceText,
     showRawTrace,
     resultView,
+    isRunning,
   } = activeStatus;
   const MAX_ERROR_LINES = 3;
   const limitedErrorLines = (errorLines || []).slice(0, MAX_ERROR_LINES);
@@ -1141,6 +1143,7 @@ export default function App() {
   );
 
   const runTransform = debounce(async (xsltText, ver, p, tabId) => {
+    updateWorkspaceStatus(tabId, (prev) => ({ ...prev, isRunning: true }));
     const paramObj = {};
     p.forEach((pr) => {
       if (pr.name) paramObj[pr.name] = pr.value;
@@ -1181,6 +1184,7 @@ export default function App() {
           traceText: "",
           showRawTrace: false,
           resultView: "source",
+          isRunning: false,
         });
         return;
       }
@@ -1192,6 +1196,7 @@ export default function App() {
         result: data.result,
         duration: data.duration_ms,
         error: "",
+        isRunning: false,
         errorLines: [],
         isServerError: false,
         showRawTrace: false,
@@ -1218,6 +1223,7 @@ export default function App() {
         traceText: "",
         showRawTrace: false,
         resultView: "source",
+        isRunning: false,
       });
     }
   }, 500);
@@ -2060,11 +2066,16 @@ export default function App() {
         )}
         {showResultPane && (
           <>
-            {duration !== null && (
+            {isRunning ? (
+              <div className="running-box" role="status" aria-live="polite">
+                <span className="running-dot" />
+                Running…
+              </div>
+            ) : duration !== null ? (
               <div className="success-box" role="status" aria-live="polite">
                 Success in {duration} ms
               </div>
-            )}
+            ) : null}
             <div className="result-actions">
               {canRenderHtml && (
                 <button
@@ -2123,7 +2134,7 @@ export default function App() {
                 <Icon name="refresh" />
               </button>
             </div>
-            <div className="result-editor-wrap">
+            <div className={`result-editor-wrap${isRunning ? " result--loading" : ""}`}>
               {effectiveResultView === "render" && canRenderHtml ? (
                 <div className="result-render">
                   <iframe

frontend/src/style.css

@@ -356,6 +356,39 @@ a:focus-visible {
   padding: 0.5rem;
 }
 
+.running-box {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 4px 10px;
+  border-radius: 8px;
+  font-size: 13px;
+  font-weight: 600;
+  background: rgba(255, 200, 50, 0.1);
+  color: #f5c542;
+  border: 1px solid rgba(255, 200, 50, 0.25);
+}
+
+.running-dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  background: #f5c542;
+  animation: pulse-dot 1s ease-in-out infinite;
+  flex-shrink: 0;
+}
+
+@keyframes pulse-dot {
+  0%, 100% { opacity: 1; transform: scale(1); }
+  50% { opacity: 0.4; transform: scale(0.75); }
+}
+
+.result--loading {
+  opacity: 0.45;
+  pointer-events: none;
+  transition: opacity 0.15s;
+}
+
 .app-container {
   display: flex;
   flex-direction: column;