Physical ability damage / drain against a synthesist summoner in summoned eidolon

[Aiksenpains]

So, we had an encounter against some stirges, and our synthesist got hit while his eidolon was summoned around him, causing Con damage.
Given that the eidolon's physical stats essentially replace the summoner's physical stats, which of the two should take the damage? The summoner or the eidolon?

The DM in this case put the damage on the summoner, which I can understand, and we all went with, but the weird nature of the synthesist's symbiotic relationship with their eidolon has me wondering.

If the eidolon, can he just dismiss the eidolon, then resummon it with the damage gone, or is that persistent?

[David knott 242]

The eidolon should take the damage until enough is taken to banish it. Any remaining damage is taken by the summoner.

And eidolons do not automatically heal ability score damage. In the case of constitution damage, the eidolon is banished when constitution is reduced to zero, and it has a constitution of 1 when it is re-summoned.