> Socialism by definition is where the means of production cannot be individually owned

Possibly we're familiar with different strains, but my understanding is that it's less about what's individually/collectively owned and more about the relationship between the person doing the labor and the tools they're using to do that labor (ie. "do the workers own the factory or not?"). Social ownership of means of production is one proposal to achieve "workers owning the factory", but AFAIR there are alternatives.

Even granting that a central enforcement authority must exist, it's not clear to me why that enforcement implies planning. It seems to me that one could have a voluntary cooperative agreement with "town council" style enforcement of property relations (or even something like community-ownership with citizen equity), but still have unregulated trade and barter between cooperative members, or with entities outside the cooperative.

> socialist in a different context (as an ideology) may engender this in contradictory fashion.

I think it's important to also note that there isn't really a central socialist tradition; even at the outset of the movement there were disagreeing views on what properly constituted "socialism" or not. This does't mean that the internal belief systems of these traditions have some inherent contradiction, just that there are multiple paths one might take to similar conclusions, and that these don't always line up 100% when you zoom in on the details.