Found in the browser UAT, not by the gate. Moving the cap onto the arriving
bytes meant it fires while the client is still sending, and answering + closing
mid-upload is what XHR reports as a network failure: the upload dialog said
"the server couldn't be reached" while the access log showed a correct 422
carrying the limit. A refusal the client cannot read is an outage as far as the
user is concerned.
`capped_stream_to` now reads the remainder to nowhere before raising, so the
client finishes sending and reads the real answer -- re-measured in the
browser, which now names the limit. Nothing past the cap is written, and the
request is still bounded by bodylimit's ceiling, so the cost is bandwidth an
AUTHENTICATED caller was sending anyway. The anonymous path is untouched:
auth still resolves before a byte is read.
The regression test sits on the helper, not the route, and the reason is worth
keeping: the route-level version was written first and PASSED with the drain
deleted. httpx's ASGI transport pumps the request body whether or not the app
reads it, so "drained" and "abandoned" are indistinguishable through
TestClient. Its own mutation check is what exposed it.
peter
3d7ef9e945