What was the original usage of 'sentient'?

In general speech, especially in science fiction and fantasy, 'sentient' is used to mean "having human-equivalent intelligence".

But on the internet, people often insist that the original meaning of 'sentient' was "having thoughts, intelligent or otherwise" and that you should use 'sapient' instead.

But is that really true? I've never seen 'sentient' used that way except in discussions about the word and the occasional work of science fiction. I've always wondered whether it really was the original usage, or whether it was a distinction invented later.

The science fiction usage is derived from its original meaning:

Sentient:

1630s, "capable of feeling," from Latin sentientem (nominative sentiens) "feeling," present participle of sentire "to feel" (see sense (n.)).

Meaning "conscious" (of something) is from 1815.

(Etymonline)

The term is commonly used in Buddhism for instance:

In Buddhism, sentient beings are beings with consciousness, sentience, or in some contexts life itself. Sentient beings are composed of the five aggregates, or skandhas: matter, sensation, perception, mental formations and consciousness.

Sentient in science fiction:

In science fiction, an alien, android, robot, hologram or computer described as ‘sentient’ is usually treated in the same way as a human being. Foremost among these properties is human level intelligence (sapience) but sentient characters also typically display desire, will, consciousness, ethic, personality, insight and humour. Sentience is used in this context to describe an essential human property that unites all of these other qualities. The words ‘sapience’, ‘self-awareness’ and ‘consciousness’ are used in similar ways and sometimes – and confusingly –interchangeably in science fiction.

(um.edu.mt)