if csv export is truncated in non streaming mode set informative response header

[fgregg]

streaming mode is currently not enabled for custom queries, so the queries will be truncated to max row limit.

it would be great if a response is truncated that an header signalling that was set in the header.

i need to write some pagination code for getting full results back for a custom query and it would make the code much better if i could reliably known when there is nothing more to limit/offset

[fgregg]

would also be good if the header said the what the max row limit was

[fgregg]

these headers would also be relevant for json exports of custom queries

[simonw]

This is a really interesting idea - kind of similar to how many APIs include custom HTTP headers informing of rate-limits.