I tested the max limit via a button that created a lot of rows, each row increased the text length by 1 until I hit an error. I was able to create 43,661 rows, and at 43,662 Coda gave me an error for creating that row.
I reconfirmed by trying to create 1 row with 43,661 chars and it worked and then 1 row with 43,662 characters and it coda said:
So looks like the max is 43,661 characters (note I didn’t test any other types just alphanumeric).