Build History for pull/453

Make remove_dir_if_exists recursive to handle prefix subdirectories When no build_files_prefix is set, startup cleanup removes the entire build_files/ tree. The previous Sys.remove call fails on subdirectory entries left by prefixed test runs. Recurse into subdirectories before removing them. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Make remove_dir_if_exists recursive to handle prefix subdirectories When no build_files_prefix is set, startup cleanup removes the entire build_files/ tree. The previous Sys.remove call fails on subdirectory entries left by prefixed test runs. Recurse into subdirectories before removing them. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add build_files_prefix config to isolate test output directories Multiple test executables write to the same build_files/ directory, causing races when dune runs them in parallel. Add a build_files_prefix option so each test uses build_files/<prefix>/ as its output directory. - Add build_files_prefix config option (cmdline/env/config file) - Update build_file() to create prefixed subdirectories - Scope clean_up_build_files_on_startup to prefix subdirectory when set - Update all 5 dune rules that copy from build_files/ to use prefixed paths - Document new option in ocannl_config.example Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>