The investigation is written around the FilterTime_<N> option token on
/mode/vs/0, and its conclusion holds for the ARTIK051_KRAC_18K it was
measured on. An ARTIK051_PRAC_20K has no such token: no FilterTime, no
FilterAlarmTime, no FilterCleanAlarm anywhere in its options blob. It
keeps the counter in /filter/airdustfilter/vs/0 as a percentage of a
500-hour interval instead.
Neither route resets it. FilterCleanAlarm_Clear to /mode/vs/0 returns
4.00 with the options blob byte-identical; writing filterUsage as the
string "0" returns 4.00; writing it as an integer returns 5.00. That
last difference is the useful part — two payloads differing only in JSON
type returning different codes rules out an unresolved href or an
unrecognised field name, leaving read-only as the reading.
Adds a scope line to the intro and a section documenting the board, its
two resource dumps, the attempt table, and an observation-only
workaround for percentage-counter boards.
