How was "ben't" used, and when did it cease to be used?

In Jane Austen's The Watsons, the maid of the titular family utters the following sentence:

"Please, ma'am, master wants to know why he ben't to have his dinner?"

I have never encountered ben't before, and haven't been able to find much information about it through preliminary research. This source, as well as a few others I encountered, states that ben't is among the first negative contractions attested in written English, in the 1600s, but gives no clue as to when its usage ended, nor what exactly it was used for. Given that The Watsons was written in 1805 and published in 1871, the form was evidently still recognized in the 19th century.

So, my question has several parts:

1. What exactly does ben't mean - how did its usage differ from isn't, aren't, etc? (In the example above, it sounds as though it would be interchangeable with isn't.)
2. When did ben't become archaic/obsolete?
3. Were there some dialects of English in which ben't was more commonly used than others? (I ask this because in the Austen example, it's the maid who uses ben't, which leads me to hypothesize that maybe - at least by the 19th century - it was only used in some nonstandard dialect, or a lower speech register, or something of that kind.)

Solution 1:

The OED shows many forms of be that have occurred over the centuries, including numerous negative forms. Ben’t is among them, having been in use from the seventeenth century onwards, and it may still be heard in some parts of England today. It has probably always been a non-standard form, in so far as it is possible to make such distinctions before a fully standardised form of English emerged.

There are similar forms which may represent similar pronunciations, so it is may not be clear which one the maid actually used.

The supporting citations show it being used with I, with the meaning I am not, but that doesn’t necessarily mean it is not found with other persons.

Solution 2:

I encountered "ben't" for the first time in Jonathan Edwards' Treatise Concerning Religious Affections (18th c. America) Commenting on the Shema' (Hear, O Israel...), he writes, "If we ben't in good earnest in Religion, and our Wills and Inclinations ben't strongly exercised, we are Nothing." (p. 10) I realized this can only be a contraction for "be not."