Like you, I don't know if he's their long-term LT. Quite possibly not. And maybe they end up drafting who they think IS their long-term LT in late April. Who knows.
But in the meantime, as you said, they have a kid who has been reliable and played well (not great) overall and would be well worth bringing back. Team him with Avila (who should ascend in his 2nd year) on that left side. $4.8M for a reliable LT is NOT big money.
And come 2025, he's either played really well and earns himself a new contract with the Rams- or elsewhere (likely getting them a 3rd round comp. pick), or they see other, better options elsewhere.
I don't think you can go the right of first refusal route because there are plenty of teams with bad OL who would come after him. And heck, even at a 2nd round RFA tender maybe someone else does. You never know. But at least they'd be compensated if they did.
They have maneuvered their cap situation well and can fit Jackson in at $4.8M with ease while still addressing other areas
and while maintaining even more cap space in 2025.
Worst case- if you can call it "worst"- is they draft a plug-and-play LT in late April and Jackson becomes their 6th man on the OL. They paid Noteboom more than that for the same role in 2023.