fb2e623008
Five near-identical MagicMock scripts pinned the same contract (byte-exact or discard, heredoc gets exactly one extra byte); one parametrized test plus the unprobeable-backend case cover it. Drop the host-side happy-path test that duplicated test_multibyte_content_verified_by_byte_count. Docstring now names the real heredoc wrapper (BaseEnvironment._embed_stdin_heredoc) and notes the extra exec RTT per oversized result (review point).