Improve WebCRT multi-tab performance and inventory auth UX.

Keep two warm terminals, coalesce stdout per frame, trim scrollback, and allow Telnet credential prompts for managed/quick-connect targets.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/components/WebTerminal.tsx

@@ -90,7 +90,7 @@ function serializeTerminal(term: Terminal): string {
   return lines.join("\n").replace(/\s+$/g, "");
 }
 
-/** Line-wise search — avoids serializing the full 10k scrollback on every Find. */
+/** Line-wise search — avoids serializing the full scrollback on every Find. */
 function findBufferLine(
   term: Terminal,
   query: string,
@@ -402,7 +402,8 @@ export const WebTerminal = forwardRef<WebTerminalHandle, Props>(function WebTerm
       cursorBlink: true,
       fontSize: fontSizeRef.current,
       fontFamily: 'Consolas, "Courier New", monospace',
-      scrollback: 10000,
+      // Lower than CRT-style 10k: remounts + multi-tab stay lighter; server replays log tail on attach.
+      scrollback: 4000,
       theme: xtermThemeFromColors(termColorsRef.current),
       convertEol: true,
     });
@@ -443,11 +444,32 @@ export const WebTerminal = forwardRef<WebTerminalHandle, Props>(function WebTerm
 
     const isActiveSocket = () => !cancelled && wsRef.current === ws;
 
+    // Coalesce high-rate stdout into one paint frame to cut xterm write churn.
+    let writeBuf = "";
+    let writeRaf = 0;
+    const flushWriteBuf = () => {
+      writeRaf = 0;
+      const chunk = writeBuf;
+      writeBuf = "";
+      if (!chunk || cancelled) return;
+      term.write(applyKeywordHighlight(chunk, keywordHighlightRef.current));
+    };
     const writeStdout = (raw: string) => {
       if (!raw || !isActiveSocket()) return;
       lastStdoutAtRef.current = performance.now();
       if (recordingRef.current) onStdoutRef.current?.(raw);
-      term.write(applyKeywordHighlight(raw, keywordHighlightRef.current));
+      writeBuf += raw;
+      if (writeBuf.length >= 16384) {
+        if (writeRaf) {
+          cancelAnimationFrame(writeRaf);
+          writeRaf = 0;
+        }
+        flushWriteBuf();
+        return;
+      }
+      if (!writeRaf) {
+        writeRaf = requestAnimationFrame(flushWriteBuf);
+      }
     };
 
     const sendResize = () => {
@@ -640,6 +662,11 @@ export const WebTerminal = forwardRef<WebTerminalHandle, Props>(function WebTerm
 
     return () => {
       cancelled = true;
+      if (writeRaf) {
+        cancelAnimationFrame(writeRaf);
+        writeRaf = 0;
+      }
+      writeBuf = "";
       window.clearInterval(pingTimer);
       window.removeEventListener("resize", onWinResize);
       window.removeEventListener("keydown", onKeyDownCapture, true);

web/src/pages/WebcrtPage.tsx

@@ -1,6 +1,7 @@
 import {
   useCallback,
   useEffect,
+  useMemo,
   useRef,
   useState,
   type DragEvent as ReactDragEvent,
@@ -77,6 +78,8 @@ const KEEPALIVE_OPTIONS = [0, 15, 30, 60, 120] as const;
 /** Compact recording chunks before they grow unbounded (join + trim). */
 const LOG_COMPACT_CHUNKS = 1500;
 const LOG_MAX_CHARS = 8 * 1024 * 1024;
+/** Keep active + (N-1) recent tabs mounted; colder tabs detach WS/xterm until focused. */
+const WARM_TAB_LIMIT = 2;
 
 type ColorSchemeId = "dark" | "blackWhite" | "whiteBlack" | "greenBlack" | "amberBlack" | "custom";
 
@@ -343,11 +346,10 @@ function isSshAuthFailure(err: unknown): boolean {
   );
 }
 
-/** Inventory SSH (managed / webcrt Quick Connect). UME uses shared CLI profile — no per-NE popup. */
+/** Inventory managed / Quick Connect. UME uses shared CLI profile — no per-NE popup. */
-function isInventorySsh(target: Pick<CliTargetItem, "source" | "protocol">): boolean {
+function isInventoryTarget(target: Pick<CliTargetItem, "source" | "protocol">): boolean {
   const src = String(target.source || "").toLowerCase();
-  if (src !== "webcrt" && src !== "managed") return false;
+  return src === "webcrt" || src === "managed";
-  return String(target.protocol || "ssh").toLowerCase() !== "telnet";
 }
 
 function isSessionGoneError(err: unknown): boolean {
@@ -667,6 +669,8 @@ export function WebcrtPage() {
   const [page, setPage] = useState(1);
   const [tabs, setTabs] = useState<TermTab[]>([]);
   const [activeTabKey, setActiveTabKey] = useState("");
+  /** MRU tab keys for warm-mount (active always mounts via isActive even before this updates). */
+  const [warmOrder, setWarmOrder] = useState<string[]>([]);
   const [sftpOpen, setSftpOpen] = useState(false);
   const [sftpPath, setSftpPath] = useState(".");
   const [sftpBusy, setSftpBusy] = useState(false);
@@ -725,6 +729,13 @@ export function WebcrtPage() {
   const sessionOptsRef = useRef(sessionOpts);
   sessionOptsRef.current = sessionOpts;
 
+  useEffect(() => {
+    if (!activeTabKey) return;
+    setWarmOrder((prev) => [activeTabKey, ...prev.filter((k) => k !== activeTabKey)].slice(0, 16));
+  }, [activeTabKey]);
+
+  const warmTabKeys = useMemo(() => new Set(warmOrder.slice(0, WARM_TAB_LIMIT)), [warmOrder]);
+
   useEffect(() => {
     if (!optionsMenuOpen) return;
     const onDoc = (e: MouseEvent) => {
@@ -869,8 +880,8 @@ export function WebcrtPage() {
       }
       if (connectingKeysRef.current.has(key)) return;
 
-      // Managed / WebCRT SSH without saved password → credential popup (UME uses shared profile).
+      // Managed / WebCRT without saved password → credential popup (UME uses shared profile).
-      if (isInventorySsh(target) && !target.has_password && !opts?.force) {
+      if (isInventoryTarget(target) && !target.has_password && !opts?.force) {
         openAuthForTarget(target);
         return;
       }
@@ -944,7 +955,7 @@ export function WebcrtPage() {
       } catch (err) {
         const message = webcrtErrorMessage(err, t);
         const needAuth =
-          isInventorySsh(target) &&
+          isInventoryTarget(target) &&
           (String(err).includes("credentials_incomplete") ||
             String(err).includes("connect_failed") ||
             isSshAuthFailure(err));
@@ -2188,8 +2199,9 @@ export function WebcrtPage() {
               <div className="webcrt-main__terms">
               {tabs.map((tab) => {
                 const isActive = activeTabKey === tab.key;
-                // Only the active tab mounts xterm + WS; background tabs detach and re-attach on focus.
+                // Cap concurrent xterm+WS: active always mounts; keep one recent background warm.
-                const mountTerminal = Boolean(isActive && tab.wsUrl);
+                // Colder tabs detach (server grace) and re-attach on focus via the same session_id.
+                const mountTerminal = Boolean(tab.wsUrl && (isActive || warmTabKeys.has(tab.key)));
                 return (
                 <div
                   key={tab.key}
@@ -2339,7 +2351,7 @@ export function WebcrtPage() {
                             if (sid) {
                               void closeWebcrtSession(sid).catch(() => undefined);
                             }
-                            if (isInventorySsh(tab.target) && isSshAuthFailure(errMsg)) {
+                            if (isInventoryTarget(tab.target) && isSshAuthFailure(errMsg)) {
                               openAuthForTarget(tab.target, webcrtErrorMessage(errMsg, t));
                             }
                           } else if (state === "closed") {