I fail to understand what surplus harvest is in this context.
What you don't need for yourself, or for whole communities, what the communities don't need. If you're currently a subsistence farmer ways will be found to make you more productive than that, e.g. by making sure that each village has a tractor at least.
I don’t see any benefit outside of situation where the export/import is impractical.
Why are you exporting food to some place while the local restaurant is importing it? Even if it's practical because you have roads and open borders and whatnot doesn't mean that it's sensible.
And, of course, there's plenty of restaurants around in the EU which source very locally. Make that the norm, instead of the exception.
Rojava, also the Zapatista, still do plenty of commodified trade -- goods against money. The base requirements that people have, though, food, shelter, education, healthcare, are decommodified. Part of the food you produce in excess goes into doctor's stomachs, the rest onto the market so that things like medical supplies can be bought, stuff Rojava doesn't produce itself.
What gets distributed, what gets sold and what gets bought is all council decisions.