OptionalprepOptionalreservedThe reserved async-override flag consumed from the token stream, if
any: --async / --sync (last wins). These are framework-reserved
flags stripped ahead of per-command option binding, not per-command
options — so they work on any verb. undefined = no override; the
verb's CommandDefinition.async spec default applies. Consumed in
CommandGiverMixin._runChain to compute the effective async mode.
assemblesuccess arm.prepcarries any prepositions consumed per positional field — keyed by field name, lowercased value. Absent (or empty) when no field declaredprepositions:.