The endSpan closure accepted error by value, meaning deferred calls like
defer spanEnd(err) captured the error at defer-time (always nil), not at
function-return time. This meant errors were never recorded on spans.
- Changed endSpan to accept *error
- Updated all call sites in rpc/handler.go to pass error pointers, and
adjusted handleCall to avoid propagating child-span errors to the parent
- Added TestTracingHTTPErrorRecording to verify that errors from RPC
methods are properly recorded on the rpc.runMethod span
d8b92cb9e6