Adding a new field from the editor then resetting the template from Card Layouts causes an error

[abdnh]

Steps to reproduce

Make a basic note.
Open it in the note editor.
Click on fields and add a field.
Click on cards then restore to default from the upper right corner.

Actual behavior
You get an error “note has 3 fields, expected 2”.
Expected behavior
No error.
Additional information
On AnkiDroid, you don’t get an error immediately, but if you try to save the edit, you get this error
java.lang.lndexOutOfBoundsException: Index 2 out of bounds for length 2

Debug info
Anki 25.09.2 (3890e12) (ao)
Python 3.13.5 Qt 6.9.1 PyQt 6.9.1
Platform: Windows-10-10.0.19045-SP0

===Add-ons (active)===
(add-on provided name [Add-on folder, installed at, version, is config changed])
Advanced Copy Fields ['1898445115', 2024-01-08T20:01, 'v0.4.01', '']
AnkiConnect ['2055492159', 2025-11-09T22:40, 'None', mod]
AnkiWebView Inspector ['31746032', 2023-06-27T22:26, 'None', '']
Disconnected Review-Log Cleaner ['1067771610', 2025-06-10T16:28, 'None', '']
Local Audio Server for Yomichan ['1045800357', 2023-06-19T06:57, 'None', '']
The KING of Button Add-ons ['374005964', 2025-01-28T01:26, 'None', mod]

===IDs of active AnkiWeb add-ons===
1045800357 1067771610 1898445115 2055492159 31746032 374005964

===Add-ons (inactive)===
(add-on provided name [Add-on folder, installed at, version, is config changed])
No Distractions Full Screen Fixed by Shige ['1370336700', 2024-08-26T08:08, 'None', mod]

Originally reported on https://forums.ankiweb.net/t/error-restore-to-default-note-has-3-fields-expected-2/68718

Reproducible in #4029 but it's only a console error there.

[GithubAnon0000]

This is what I see on debian linux (both 13 and sid):

Anki.mp4

I cannot reproduce here.

[abdnh]

The issue probably depends on timing. If you test with #4029, I assume you'd see a console error consistently.

[GithubAnon0000]

I build 0e7aa1f and when I add a new field I get this:

Traceback (most recent call last):
  File "/media/anon/separateDownload/anki/Source_Code/anki/qt/aqt/mediasrv.py", line 1080, in wrapped
    result = handler()
  File "/media/anon/separateDownload/anki/Source_Code/anki/qt/aqt/mediasrv.py", line 1035, in wrapped
    output = getattr(aqt.mw.col._backend, f"{endpoint}_raw")(request.data)
  File "/media/anon/separateDownload/anki/Source_Code/anki/out/pylib/anki/_backend_generated.py", line 1485, in update_notes_raw
    return self._run_command(25, 5, message)
           ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/media/anon/separateDownload/anki/Source_Code/anki/pylib/anki/_backend.py", line 171, in _run_command
    raise backend_exception_to_pylib(err)
anki.errors.InvalidInput: note has 2 fields, expected 3

But I do not get that after resetting the note. Resetting just works fine. See video:

Anki.mp4