Intent is indeed hard to prove, but it is a crucial concept under the law. From your original post it sounded like you and your family really did intend to move to WA (i.e. to change your domicile). My previous answer assumes that this was the case. The best proof (if you were challenged) would be things like a Washington drivers license, car registration, voter registration, etc. - if you happened to have obtained any of these.
But if your move to Washington was temporary, with your intent being to return to your home in Oregon, then OR would have remained your domicile state all along, which would make all your income during your time away still taxable by OR.
Here's a link to the Oregon law defining the concept of "domicile":
https://oregon.public.law/statutes/ors_15.420
Note particularly that your domicile does not change until it is superseded by the acquisition of a new domicile. And note the law's use of the word "intent".
(Note also that Oregon's 200-day rule applies to individuals who are not domiciled in OR, but who spend more than 200 days of the tax year in OR.)
Bottom line: it all comes down to whether or not your move to WA constituted a change in domicile. If it did not, then all your 2023 income be taxable By Oregon, and you would file a 2023 Oregon tax return as a resident.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
