which is it: hardy har har, or hearty har har, or?

Well, I've never seen it written out. (See tsuwm's link for that.) And, in my dialect, an intervocalic voiceless dental stop is realized as /ɾ/ (an alveolar flap or tap, see link). (And, that's not a /d/ as some Brits erroneously seem think.)

Ceci n'est pas un seing.