feat(ui): add customizable status line

Allow users to configure a custom shell command to display in the UI footer status line.

packages/cli/src/ui/hooks/useStatusLine.ts

@@ -0,0 +1,63 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useState, useEffect } from 'react';
+import { exec } from 'child_process';
+import { useSettings } from '../contexts/SettingsContext.js';
+import { isShellCommandReadOnlyAST } from '@qwen-code/qwen-code-core';
+
+export function useStatusLine(): string | null {
+  const settings = useSettings();
+  const statusLineCommand = settings.merged.ui?.statusLine;
+  const [output, setOutput] = useState<string | null>(null);
+
+  useEffect(() => {
+    if (!statusLineCommand) {
+      setOutput(null);
+      return;
+    }
+
+    let isMounted = true;
+
+    const executeCommand = async () => {
+      try {
+        const isReadOnly = await isShellCommandReadOnlyAST(statusLineCommand);
+        if (!isReadOnly) {
+          if (isMounted) setOutput('⚠️ Sandbox: Command must be read-only');
+          return;
+        }
+
+        exec(
+          statusLineCommand,
+          { timeout: 5000, maxBuffer: 1024 * 10 },
+          (error, stdout) => {
+            if (!isMounted) return;
+            if (!error && stdout) {
+              setOutput(stdout.trim().split('\n')[0] || null);
+            } else {
+              setOutput(null);
+            }
+          },
+        );
+      } catch {
+        if (isMounted) setOutput('⚠️ Sandbox: Verification failed');
+      }
+    };
+
+    // Execute immediately
+    executeCommand();
+
+    // Poll every 5 seconds
+    const interval = setInterval(executeCommand, 5000);
+
+    return () => {
+      isMounted = false;
+      clearInterval(interval);
+    };
+  }, [statusLineCommand]);
+
+  return output;
+}