Fatigue Considerations: Over-tightened Front Derailleur Dent
Personally I'd stay far, far away, it's not worth the risk. Especially as you intend to load the bike up for bike-packing.

Cracks are not the problem. Structural tubes are severely weakened when they are buckled inwards too much. That looks like too much to me. Also, such deformation is likely to have work-hardened the steel.

The only way to repair this would be to replace the whole seat tube - which would cost more than the frame.