feat(web): persistent workspace terminal across tab switches

apps/next/src/components/agent-workspace/agent-workspace-shell.tsx

@@ -26,6 +26,7 @@ import {
   AlertDialogTitle,
   AlertDialogTrigger,
   Button,
+  cn,
   Tabs,
   TabsContent,
   TabsList,
@@ -681,11 +682,19 @@ export const AgentWorkspaceShell = ({ jobId }: { jobId: Id<'agentJobs'> }) => {
             </TabsContent>
             <TabsContent
               value='terminal'
-              className='m-0 min-h-0 flex-1 overflow-hidden'
+              forceMount
+              className={cn(
+                'm-0 min-h-0 flex-1 overflow-hidden',
+                activeWorkspaceTab !== 'terminal' && 'hidden',
+              )}
             >
               <WorkspaceTerminal
                 jobId={jobId}
-                active={activeWorkspaceTab === 'terminal' && workspaceReady}
+                active={workspaceReady}
+                visible={activeWorkspaceTab === 'terminal'}
+                waitingLabel={
+                  workspacePending ? 'Waiting for workspace…' : undefined
+                }
               />
             </TabsContent>
             <TabsContent value='diff' className='m-0 min-h-0 flex-1'>

apps/next/src/components/agent-workspace/workspace-terminal.tsx

@@ -5,12 +5,18 @@ import { XtermSession } from './xterm-session';
 export const WorkspaceTerminal = ({
   jobId,
   active,
+  visible = true,
+  waitingLabel,
 }: {
   jobId: string;
   active: boolean;
+  visible?: boolean;
+  waitingLabel?: string;
 }) => (
   <XtermSession
     active={active}
+    visible={visible}
+    waitingLabel={waitingLabel}
     tokenUrl={`/api/agent-jobs/${jobId}/terminal-token`}
     sessionKey={jobId}
   />

apps/next/src/components/agent-workspace/xterm-session.tsx

@@ -71,6 +71,7 @@ const lightTheme: ITheme = {
 
 export const XtermSession = ({
   active,
+  visible = true,
   tokenUrl,
   sessionKey,
   waitingLabel,
@@ -78,6 +79,7 @@ export const XtermSession = ({
   label = 'workspace shell',
 }: {
   active: boolean;
+  visible?: boolean;
   tokenUrl: string;
   sessionKey: string;
   waitingLabel?: string;
@@ -86,9 +88,11 @@ export const XtermSession = ({
 }) => {
   const containerRef = useRef<HTMLDivElement>(null);
   const termRef = useRef<Terminal | null>(null);
+  const fitRef = useRef<{ fit: () => void } | null>(null);
+  const wsRef = useRef<WebSocket | null>(null);
   const { resolvedTheme } = useTheme();
   const themeIsLight = resolvedTheme === 'light';
-  const [status, setStatus] = useState<XtermStatus>('connecting');
+  const [status, setStatus] = useState<XtermStatus>('idle');
   const [errorText, setErrorText] = useState<string>();
   const [reconnectKey, setReconnectKey] = useState(0);
 
@@ -158,6 +162,7 @@ export const XtermSession = ({
       term.loadAddon(new WebLinksAddon());
       term.open(container);
       termRef.current = term;
+      fitRef.current = fit;
 
       // Task 11 will wire clipboard copy-on-select behavior here. Accept the
       // prop now so callers (and the effect deps) are stable across that change.
@@ -193,6 +198,7 @@ export const XtermSession = ({
       });
 
       ws = new WebSocket(url);
+      wsRef.current = ws;
       ws.binaryType = 'arraybuffer';
       ws.onopen = () => {
         if (isAborted()) return;
@@ -233,24 +239,51 @@ export const XtermSession = ({
       ws?.close();
       termRef.current?.dispose();
       termRef.current = null;
+      fitRef.current = null;
+      wsRef.current = null;
     };
     // resolvedTheme intentionally excluded: handled by the theme effect above.
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [active, sessionKey, reconnectKey]);
 
+  // A hidden (display:none) container measures 0×0, so xterm mis-sizes while the
+  // tab is inactive. When the terminal becomes visible again, refit inside a
+  // frame (so layout has settled) and push the new dimensions to the PTY. The
+  // WebSocket stays open across visibility changes — this never reconnects.
+  useEffect(() => {
+    if (!visible || !active) return;
+    const frame = requestAnimationFrame(() => {
+      try {
+        fitRef.current?.fit();
+      } catch {
+        // ignore transient layout errors
+      }
+      const ws = wsRef.current;
+      const term = termRef.current;
+      if (ws?.readyState === WebSocket.OPEN && term) {
+        ws.send(
+          JSON.stringify({ type: 'resize', cols: term.cols, rows: term.rows }),
+        );
+      }
+    });
+    return () => cancelAnimationFrame(frame);
+  }, [visible, active]);
+
   return (
     <div className='relative flex h-full min-h-0 flex-col'>
       <div className='border-border flex h-10 flex-none items-center justify-between gap-3 border-b px-3'>
         <p className='text-muted-foreground text-xs'>
           {status === 'connected'
             ? `Connected · ${label}`
-            : status === 'connecting'
-              ? 'Connecting…'
-              : status === 'closed'
-                ? 'Session ended'
-                : status === 'unconfigured'
-                  ? 'Terminal not configured'
-                  : 'Connection error'}
+            : status === 'idle'
+              ? (waitingLabel ? 'Waiting…' : 'Idle')
+              : status === 'connecting'
+                ? 'Connecting…'
+                : status === 'closed'
+                  ? 'Session ended'
+                  : status === 'unconfigured'
+                    ? 'Terminal not configured'
+                    : 'Connection error'}
         </p>
         {status === 'closed' || status === 'error' ? (
           <Button

apps/next/tests/component/xterm-session.test.tsx

@@ -3,10 +3,15 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 import { XtermSession } from '../../src/components/agent-workspace/xterm-session';
 
-const { openSpy, wsInstances, fetchSpy } = vi.hoisted(() => ({
+const { openSpy, wsInstances, fetchSpy, fitSpy } = vi.hoisted(() => ({
   openSpy: vi.fn(),
-  wsInstances: [] as Array<{ url: string }>,
+  wsInstances: [] as Array<{
+    url: string;
+    send: ReturnType<typeof vi.fn>;
+    close: ReturnType<typeof vi.fn>;
+  }>,
   fetchSpy: vi.fn(),
+  fitSpy: vi.fn(),
 }));
 
 class FakeTerminal {
@@ -30,7 +35,7 @@ class FakeTerminal {
 vi.mock('@xterm/xterm', () => ({ Terminal: FakeTerminal }));
 vi.mock('@xterm/addon-fit', () => ({
   FitAddon: class {
-    fit = vi.fn();
+    fit = fitSpy;
   },
 }));
 vi.mock('@xterm/addon-web-links', () => ({
@@ -60,6 +65,7 @@ class FakeWebSocket {
 beforeEach(() => {
   wsInstances.length = 0;
   openSpy.mockClear();
+  fitSpy.mockClear();
   fetchSpy.mockReset();
   fetchSpy.mockResolvedValue({
     ok: true,
@@ -127,4 +133,64 @@ describe('XtermSession', () => {
     expect(wsInstances[0]?.url).toBe('ws://x');
     expect(openSpy).toHaveBeenCalled();
   });
+
+  it('refits and sends a resize frame when it becomes visible', async () => {
+    const { rerender } = render(
+      <XtermSession
+        active
+        visible={false}
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+
+    await waitFor(() => expect(wsInstances).toHaveLength(1));
+    const ws = wsInstances[0]!;
+    // Ignore fits/sends from the initial connect; only the visible toggle matters.
+    fitSpy.mockClear();
+    ws.send.mockClear();
+
+    rerender(
+      <XtermSession
+        active
+        visible
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+
+    await waitFor(() => expect(fitSpy).toHaveBeenCalled());
+    await waitFor(() =>
+      expect(ws.send).toHaveBeenCalledWith(
+        expect.stringContaining('"type":"resize"'),
+      ),
+    );
+  });
+
+  it('keeps the WebSocket open when hidden while still active', async () => {
+    const { rerender } = render(
+      <XtermSession
+        active
+        visible
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+
+    await waitFor(() => expect(wsInstances).toHaveLength(1));
+    const ws = wsInstances[0]!;
+
+    rerender(
+      <XtermSession
+        active
+        visible={false}
+        tokenUrl='/api/box/terminal-token'
+        sessionKey='box-1'
+      />,
+    );
+    await Promise.resolve();
+
+    expect(ws.close).not.toHaveBeenCalled();
+    expect(wsInstances).toHaveLength(1);
+  });
 });