The abort timer was cleared as soon as fetch resolved with headers, so
a server that stalled the response body hung the request forever - and
one hung run froze the autonomous queue behind the worker re-entrancy
guard. JSON requests now carry a header deadline plus a longer body
deadline on one abort controller, and event streams fail when no chunk
arrives within an idle window, cancelling the reader. Timeouts surface
as ProviderHttpError so the run records a clear failure and the
heartbeat retries.
