The gemara is mashma it’s a middus chassidis, SA brings it l’halacha. The nosei keilim point out this issue.
It would seem that in the time of the gemara it was not standard practice for all but by the times of the early achronim it was already widely accepted as compulsory. Perhaps during the times of the rishonim the minhag spread, I really don’t know. Maybe someone else knows more about the history of it. A Jewish History professor would be a good person to ask- YU has some widely respected and knowledgeable professors who may be able to answer this.
Certainly today it would be considered halacha pesuka in SA and fall under the umbrella of al titash toras imecha.
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