mock_access() uses mockfs_open(RDONLY) to probe whether a path exists in the mock filesystem, then immediately closes the handle. Directories are detected via the MOCKFS_ERRNO_ISDIR return from mockfs_open. This prevents the simulation from falling back to file_open(O_CREAT), which would create empty files as a side effect and corrupt chunk data. https://claude.ai/code/session_01YJnNDYw8JVb4HPSMf9rpuS