...and on the other side Mary's agent would summarize your greeting as part of her regular notification digest. There would be no gradient. You and your correspondent would continue to pay equivalent proportion of available attention to each other; thus you would remain equally human as before.

At least relative to each other (and to each of the rest of your contacts.)

It's one's idea of humanness that will be substituted piecemeal by a "doppelganger concept", as a result of the perceptual decoupling provided by ever-thicker interfaces. That concept would continue to fulfill the exact same function in one's life that formerly would've been fulfilled by one's previous opinions on "what it means to be human" (if any).

Happens all the time, things changing people's minds. Happens surreptitiously, too. Of course, it's more comfortable to consider at least our inner lives remain inviolate to the vagaries of technocapital - but where could all their content come from, other than entirely from the outside world, same one that software was proclaimed to be "eating"?

Subjectively, you'd hardly (if ever) experience that kind of "world model spoofing" as anything close to a distinctly recognizable perceptual phenomenon (since it's language-based anyway). Rather, you'd continue to experience everything as the usual "being a person comprehending a world" bit - and, as ever, flavored by whatever life-scripts you've been allocated.

On average, however, the substitution would result in effects as simple as the population allocating that much more of its resources to, say, the organization representing the machinic quasi-intelligence in question - the one that has interposed itself as normative communication medium by providing useful summaries.

Or, not as simple.

It's already ended up very much like that "isn't there someone you forgot to ask" meme. Except the 3rd party pictured as JC, should rather be labeled "VC".