@Steve ******
„and for some reason the IO gave me a visa expiration date of 29 November 2025”
No. He didn’t give you a “new visa expiration date”
He gave you a STAY PERMIT which is valid until November 29, 2025
Your “visa expiration date” is still December this year.
After the expiry of your visa validity, you have no re-entry permit any more.
So if you were to exit Thailand in February for a few weeks, you would need to buy a single re-entry permit in order to keep your stay permit until 29 November 2025 alive.
You do not have to do the “1-year extension of stay permit” by next week, yet.
You can wait until 29 October 2025, before you apply for the “1-Year Extended Stay Permit”