Windows OpenSSH 9.5 blocks while writing captured stderr to a pipe, even with stdin disconnected and a connection timeout. Capture stderr in a temporary file for one-shot OpenSSH calls on Windows, preserving subprocess output, text, check, and timeout behavior. Leave POSIX capture unchanged.
Use the shared runner for SSH, scp, key lookup, and streamed app-data transfers. Bound the real ssh-keygen hashing tests and keep their assertions; move the transfer-error mock to the runner seam. Add ten regression tests.
Verified the full suite on Windows 11 with bundled Python 3.12.14: 628 tests, OK (110 existing skips), 42.685s. Verified macOS Python 3.9.6: 628 tests, OK, 67.934s. Independent Codex gpt-6-sol high-reasoning review found no actionable issues. Protected RDP code is unchanged.
Co-Authored-By: GPT-6.1 Sol (Codex) <noreply@openai.com>
