feat: harden plugin api for separate repos, signed updates and generic external login

plugins/ssh-terminal/src/frontend/look/theme-preview.ts

@@ -0,0 +1,30 @@
+import { useSyncExternalStore } from "react";
+
+/**
+ * The terminal theme the host editor is previewing, so an open terminal for
+ * that host can show it before the host is saved. Null when nothing is being
+ * previewed.
+ */
+let preview: string | null = null;
+const listeners = new Set<() => void>();
+
+export function setThemePreview(theme: string | null): void {
+  if (theme === preview) return;
+  preview = theme;
+  for (const listener of listeners) listener();
+}
+
+function subscribe(listener: () => void): () => void {
+  listeners.add(listener);
+  return () => {
+    listeners.delete(listener);
+  };
+}
+
+export function useThemePreview(): string | null {
+  return useSyncExternalStore(
+    subscribe,
+    () => preview,
+    () => preview,
+  );
+}