feat(webui): govern actions, quick access, and metrics

Refs #264, #285, #289

webui/src/components/UnsavedChangesContext.ts

@@ -0,0 +1,30 @@
+import { createContext, useContext } from "react";
+
+export type UnsavedNavigationAction = () => void;
+
+export type UnsavedChangesRegistration = {
+  title?: string;
+  message?: string;
+  onSave: () => boolean | Promise<boolean>;
+  onDiscard?: () => void;
+};
+
+export type UnsavedChangesContextValue = {
+  hasUnsavedChanges: boolean;
+  registerUnsavedChanges: (registration: UnsavedChangesRegistration | null) => () => void;
+  requestNavigation: (action: UnsavedNavigationAction) => void;
+  requestDiscard: (action: UnsavedNavigationAction) => void;
+};
+
+export const UnsavedChangesContext = createContext<UnsavedChangesContextValue | null>(null);
+
+const fallbackUnsavedChangesContext: UnsavedChangesContextValue = {
+  hasUnsavedChanges: false,
+  registerUnsavedChanges: () => () => undefined,
+  requestNavigation: (action) => action(),
+  requestDiscard: (action) => action()
+};
+
+export function useUnsavedChanges() {
+  return useContext(UnsavedChangesContext) ?? fallbackUnsavedChangesContext;
+}