Expose an fs.exists over the context bridge

desktop/src/main/fs.ts

@@ -0,0 +1,6 @@
+/**
+ * @file file system related functions exposed over the context bridge.
+ */
+import { existsSync } from "node:fs";
+
+export const fsExists = (path: string) => existsSync(path);

desktop/src/main/ipc.ts

@@ -10,6 +10,7 @@ import { ipcMain } from "electron/main";
 import { appVersion } from "../services/appUpdater";
 import { openDirectory, openLogDirectory } from "./general";
 import { logToDisk } from "./log";
+import { fsExists } from "./fs";
 
 // - General
 
@@ -40,4 +41,6 @@ export const attachIPCHandlers = () => {
 
     // See: [Note: Catching exception during .send/.on]
     ipcMain.on("logToDisk", (_, msg) => logToDisk(msg));
+
+    ipcMain.handle("fsExists", (_, path) => fsExists(path));
 };

desktop/src/preload.ts

@@ -88,6 +88,13 @@ const openLogDirectory = (): Promise<void> =>
 const logToDisk = (message: string): void =>
     ipcRenderer.send("logToDisk", message);
 
+/**
+ * Return true if there is a file or directory at the given
+ * {@link path}.
+ */
+const fsExists = (path: string): Promise<boolean> =>
+    ipcRenderer.invoke("fsExists", path);
+
 // - FIXME below this
 
 /* preload: duplicated logError */
@@ -429,6 +436,11 @@ contextBridge.exposeInMainWorld("ElectronAPIs", {
     skipAppUpdate,
     muteUpdateNotification,
 
+    // - FS
+    fs: {
+        exists: fsExists,
+    },
+
     // - Export
     exists,
     checkExistsAndCreateDir,

web/packages/shared/electron/types.ts

@@ -50,6 +50,34 @@ export interface ElectronAPIsType {
      */
     logToDisk: (message: string) => void;
 
+    /**
+     * A subset of filesystem access APIs.
+     *
+     * The renderer process, being a web process, does not have full access to
+     * the local filesystem apart from files explicitly dragged and dropped (or
+     * selected by the user in a native file open dialog).
+     *
+     * The main process, however, has full filesystem access (limited only be an
+     * OS level sandbox on the entire process).
+     *
+     * When we're running in the desktop app, we want to better utilize the
+     * local filesystem access to provide more integrated features to the user -
+     * things that are not currently possible using web technologies. For
+     * example, continuous exports to an arbitrary user chosen location on disk,
+     * or watching some folders for changes and syncing them automatically.
+     *
+     * Towards this end, this fs object provides some generic file system access
+     * functions that are needed for such features. In addition, there are other
+     * feature specific methods too in the top level electron object.
+     */
+    fs: {
+        /**
+         * Return true if there is a file or directory at the given
+         * {@link path}.
+         */
+        exists: (path: string) => Promise<boolean>;
+    };
+
     exists: (path: string) => boolean;
     checkExistsAndCreateDir: (dirPath: string) => Promise<void>;
     saveStreamToDisk: (