feat(extension): expose host version and WebView page events

internal/webview/extension-api.d.ts

@@ -0,0 +1,48 @@
+/** Public extension API additions. info.version remains the extension version. */
+export interface ExtensionInfo {
+  identity: string;
+  name: string;
+  author: string;
+  title: string;
+  version: string;
+  hostVersion: string;
+}
+
+/** Functions are serialized; they cannot capture extension-side variables. */
+export type WebviewExecutable<T = unknown> =
+  | string
+  | ((...args: unknown[]) => T | Promise<T>);
+
+export type WebviewUnsubscribe = () => void;
+
+/** Navigation and load notifications are for the main document only. */
+export interface WebviewEventMap {
+  "url-changed": { url: string; sameDocument: boolean };
+  /** window.load, including reloads, excluding hash/History API navigation. */
+  "load": { url: string };
+  "load-error": { url: string; message: string };
+  "closed": { reason: "user" | "api" };
+}
+
+export interface WebviewGotoOptions {
+  timeoutMs?: number;
+  waitUntil?: "load" | "domcontentloaded";
+}
+
+/** These members extend the existing WebviewPage API. */
+export interface WebviewPage {
+  /**
+   * Resolves when listening is ready. Does not replay current state.
+   * Register before goto() to observe navigation. Unsubscribe is idempotent.
+   * Closed is delivered once, then listeners are released automatically.
+   * Callbacks cannot cancel navigation; returned promises are not awaited.
+   * Callers handle errors in asynchronous callbacks.
+   */
+  on<K extends keyof WebviewEventMap>(
+    event: K,
+    handler: (data: WebviewEventMap[K]) => void,
+  ): Promise<WebviewUnsubscribe>;
+  /** Runs at document creation on future navigations, never immediately. */
+  addInitScript(script: string): Promise<void>;
+  goto(url: string, opts?: WebviewGotoOptions): Promise<void>;
+}