this is all handled on Form 8606, suggest working thru that for your situation.
For 2024 filing Form 8606, the additional 3k 2024 contribution made in 2025 is included in line 1, but then set aside by subtracting it on lines 4/5 and not included in the tax calculation for the 4k Roth conversion. The 3k basis left behind that wasn't converted in 2024 is then carried over to 2025.
For 2025 filing Form 8606 you would have the 3k basis carried over from 2024, plus the 2025 contribution of 7k so have a total basis 10k, and a conversion for 10k.
