Summary

• stop reliable stream flushing when send_message reports a send failure
• restore the prepared reliable buffer state so the same buffer can be retried on the next flush
• add a regression test for failed reliable stream sends

Fixes #411.

Testing

• git diff --check
• git ls-files --eol src\c\core\session\session.c src\c\core\session\stream\output_reliable_stream.c src\c\core\session\stream\output_reliable_stream_internal.h test\unitary\session\Session.cpp

Not run: unit tests. This Windows environment does not have CMake or a C/C++ compiler available in PATH (cmake --version is not recognized; Get-Command cmake,gcc,g++,clang,clang++,cl,ninja,ctest found no commands).