CSRF token staleness causes all POST requests to fail after token rotation

Extracted from #3227 by @eals2019:

Root cause

File: src/js/api-interface.js, line 6

import axios from '@nextcloud/axios';

const instance = axios.create();   // line 6 — ❌

@nextcloud/axios automatically subscribes the default axios instance to Nextcloud's csrf-token-update events, keeping the requesttoken header current across token rotations. However, axios.create() produces a new, independent instance that does not inherit those event subscriptions. The instance receives the correct CSRF token at page load but becomes stale if Nextcloud rotates the token during a long-running session, causing all subsequent POST requests (directory change, reindex, recipe save) to fail with a server-side CSRF validation error.

This can be confirmed in the server log (nextcloud.log):

{
  "method": "POST",
  "url": "/apps/cookbook/webapp/reindex",
  "message": "CSRF check failed"
}

Fix

Subscribe instance to CSRF token updates immediately after creation, mirroring what @nextcloud/axios does internally for its own instance:

import axios from '@nextcloud/axios';
import { onRequestTokenUpdate } from '@nextcloud/auth';  // ✅ add import

const instance = axios.create();

// Keep instance in sync with Nextcloud CSRF token rotations
onRequestTokenUpdate((token) => {           // ✅ add this block
    instance.defaults.headers.requesttoken = token;
});

Alternatively, avoid .create() entirely and use the @nextcloud/axios default export directly, since it already handles token rotation. All interceptors currently added to instance (request/response logging) would need to be moved to the default axios export in that case.

Start in src/js/api-interface.js at the axios.create() call and compare it with @nextcloud/axios token-update behavior. Reproduce or inspect the CSRF failure in nextcloud.log, then verify that the instance receives rotated tokens and that POST actions such as reindexing no longer fail.