thanks for your response and sorry it took me a while to return to this, I was distracted elsewhere.
It seems the Data Interpreter does not help here: it says it is not available when there is more than 3000 rows in the data and my CSV dump is currently at 87500 rows. (Also I'm a bit baffled by the idea that the Data Interpreter chooses to be not available if Tableau *itself* thinks it doesn't need help with the data...)
But back to the original question. How do I format the data to make sure that Tableau sees the column breaks as intended? Can I encapsulate non-numeric (i.e. text) columns in "quotes" for example, and maybe backslash-escape the quote character in the data? Do I then need to protect other characters? It would be very useful to find actual technical documentation on this, not Excel screenshots.
Alternatively we could switch the data dump format to JSON, it has an exact specification how tokens are interpreted, while CSV is whatever anyone calls CSV.