May 2, 2026

The Linux-only test failure

(electrum__blockchain_outpoint_subscribe__two_spenders__one_notification) demonstrates that this ordering is not observed on Ubuntu 24.04 with the Boost.Asio version used in the CI jobs, even though the same code path produces the expected ordering on Windows and macOS. This can only be explained as a platform-specific behavioral difference (or bug) in Boost.Asio's epoll-based reactor and thread-pool executor implementation on Linux.
The isolated cause of the test failures is therefore the reliance, in the two-spender notification path of complete_outpoint_subscribe, on an ordering guarantee that Boost.Asio's Linux implementation does not reliably provide in this configuration.