Fix getUsersNoteFileExtension() returning a function in React windows

In an HTML/React window DataStore is an async bridge proxy: every property
access returns a function, so the truthiness check in
getUsersNoteFileExtension() returned that function instead of a string.
makeCalendarFilename() then stringified it, producing filenames like
"20260829.function(...args) { return sendBridgeCall(...) }".

Visible in the Dashboard's Add-to-any-note dialog: picking a date in the
NoteChooser calendar picker filled the Note field (and the heading-chooser's
sourceNote) with that function source.

- NPFileExtensions: only trust an actual non-empty string; fall back to
  DEFAULT_NOTE_FILE_EXTENSION for anything else. Trim and strip a leading dot.
- NoteChooser: match the picked date against loaded notes on the filename
  without its extension, since a React window can't know the real extension.
- Tests for the bridge-function case, non-string values, and trimming.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: dwertheimer

helpers/NPFileExtensions.js

@@ -19,12 +19,16 @@ export const DEFAULT_NOTE_FILE_EXTENSION: string = SUPPORTED_NOTE_FILE_EXTENSION
 
 /**
  * User's note file extension without leading dot (DataStore preference, or DEFAULT_NOTE_FILE_EXTENSION).
+ * Note: in a React/HTML window `DataStore` is an async bridge proxy, so every property access returns a
+ * function rather than the underlying value. Only an actual non-empty string is trusted here; anything
+ * else (function, Promise, empty string, missing DataStore) falls back to DEFAULT_NOTE_FILE_EXTENSION.
  * @returns {string}
  */
 export function getUsersNoteFileExtension(): string {
   try {
-    if (DataStore.defaultFileExtension) {
-      return DataStore.defaultFileExtension
+    const ext = DataStore.defaultFileExtension
+    if (typeof ext === 'string' && ext.trim() !== '') {
+      return ext.trim().replace(/^\./, '')
     }
   } catch {
     /* use fallback */

helpers/__tests__/NPFileExtensions.test.js

@@ -96,6 +96,28 @@ describe(`${PLUGIN_NAME}`, () => {
         expect(getUsersNoteFileExtension()).toBe(DEFAULT_NOTE_FILE_EXTENSION)
       })
 
+      test('returns default when defaultFileExtension is a function (React/HTML window bridge proxy)', () => {
+        // In a React/HTML window every DataStore property access returns an async bridge function,
+        // which is truthy - returning it built filenames like "20260829.function(...args) {...}".
+        // $FlowFixMe[incompatible-type] - deliberately wrong type, to mimic the WebView bridge
+        DataStore.defaultFileExtension = function (...args) {
+          return Promise.resolve(args)
+        }
+        expect(getUsersNoteFileExtension()).toBe(DEFAULT_NOTE_FILE_EXTENSION)
+        expect(makeCalendarFilename('20260829')).toBe(`20260829.${DEFAULT_NOTE_FILE_EXTENSION}`)
+      })
+
+      test('returns default when defaultFileExtension is not a string', () => {
+        // $FlowFixMe[incompatible-type] - deliberately wrong type
+        DataStore.defaultFileExtension = { then: () => {} }
+        expect(getUsersNoteFileExtension()).toBe(DEFAULT_NOTE_FILE_EXTENSION)
+      })
+
+      test('trims whitespace and any leading dot', () => {
+        DataStore.defaultFileExtension = ' .txt '
+        expect(getUsersNoteFileExtension()).toBe('txt')
+      })
+
       test('returns default when DataStore access throws', () => {
         const savedDataStore = global.DataStore
         global.DataStore = {

helpers/react/DynamicDialog/NoteChooser.jsx

@@ -399,8 +399,14 @@ export function NoteChooser({
 
       logDebug('NoteChooser', `handleCalendarDateSelect: calendarFilename="${calendarFilename}", dateISO="${dateISO}"`)
 
-      // Find the note in the notes array or create a new option
-      const existingNote = notes.find((note) => note.filename === calendarFilename || note.filename.endsWith(`/${calendarFilename}`))
+      // Find the note in the notes array or create a new option.
+      // Match on the date part only: in a React window the user's real file extension isn't knowable,
+      // so calendarFilename falls back to the default one and wouldn't match a .txt vault's note.
+      const calendarFilenameBase = calendarFilename.replace(RE_NOTE_FILE_EXTENSION, '')
+      const existingNote = notes.find((note) => {
+        const noteFilenameBase = note.filename.replace(RE_NOTE_FILE_EXTENSION, '')
+        return noteFilenameBase === calendarFilenameBase || noteFilenameBase.endsWith(`/${calendarFilenameBase}`)
+      })
 
       logDebug('NoteChooser', `handleCalendarDateSelect: existingNote=${existingNote ? `found: ${existingNote.title}` : 'not found'}`)