The salient fact about unemployment is that anyone who stays in that state faces destitution and is likely seeking some other work (we rarely talk about wealthy heirs being "unemployed"). For someone in a premodern agricultural lifestyle there wasn't really anything calamitous about this regular period of not-working.
Nothing calamitous other than the inability to compensate for crop failures which periodically left families starving. They didn't have to worry about repossessions of course, on the basis they were closer to being property than owning property. The salient fact about modern unemployment in developed countries is that unemployed people (and especially seasonally un[der]employed people) generally receive more through even the meanest form of state assistance or unemployment insurance than peasants ever did, they just have much higher expectations of a bare minimum standard of living to fail to meet.
Crop failures can just as easily happen under a capitalist mode of production; this seems somewhat orthogonal to the question of whether people not working in the off-season are "unemployed." Yes, I agree that the government is more effective at providing social welfare programs than it was in the past, although probably some of that was compensated for by the greater connection to neighbors and kin that someone would have had, as compared to today. I'm not trying to cast the Middle Ages as an idyll we've fallen from.
> Crop failures can just as easily happen under a capitalist mode of production; this seems somewhat orthogonal to the question of whether people not working in the off-season are "unemployed."
The point was that if the people had employment opportunities, they'd be less likely to die from their own crops failing, either through acquiring savings during downtime to pay for food or being able to move out of farming when the crops failed. I mean, the seasonal pattern of agricultural labour still exists for millions in many developing countries, but none of them have any shortage of people who used to work on the land seeking work in their sweatshops.
I don't think it's very likely in a medieval context that, if you are experiencing crop failure, there is an abundance of food to purchase from someone else.
