Logging
mercury writes to ~/Library/Logs/mercury/mercury.log, always, appending across runs, and always down to debug whatever the terminal was asked for. One record per dispatched event carries the event, the effects it produced, and the resulting state, so a run is reconstructable afterwards.
mercury logs # records at info and above
mercury logs --level debug # widen that
Every record carries the pid of the process that wrote it, because a client verb and the daemon both append to the one file. pid= is always the writer; a field naming some other process says which, as stop's daemon= does.
Nothing is printed
println!, eprintln!, print!, eprint!, and dbg! do not appear in this codebase. Everything mercury says goes through tracing, so the log file is the whole record of a run rather than the part that did not go to a terminal. The terminal is a tracing_subscriber layer exactly as the file is.
A client verb's level is its audience:
info!is the verb's answer. It reaches stdout, and there is one per invocation.warn!anderror!are problems the user has to see. They reach stderr.debug!is what the verb did along the way. Only the file keeps it.
The daemon is different: its terminal is its log in full, filtered by --log-level.
LOG_LEVEL sets what the terminal shows and nothing else, defaulting to info.