A module's reported version is consumed: a calling module reads it
through dpm_module_info_of and decides from it whether to issue a
command. Calling dpm_module_execute the module's entire functional
surface contradicted that.
dpm_module_execute is the only entry through which a module performs
work. dpm_module_version and dpm_module_description are what it reports
about itself, read at load and served to consumers, and the contract
page in the public header now says so.