Hm I thought I'd edited this. I was mistaken,

    ssh -o IdentitiesOnly=yes terminal.shop

works as expected, however I had an IdentityAgent set, and my key was being submitted via that route.

    ssh -o IdentitiesOnly=yes -o IdentityAgent=/dev/null terminal.shop

behaves as expected; same as

    ssh -a -i /dev/null -o IdentityAgent=/dev/null terminal.shop

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