Rest is the trigger
Stone Humidifier raises maximum HP by five when you choose Rest at a rest site. Entering the room and choosing Smith does not activate that effect. This is different from Eternal Feather, which heals as the site is entered.
The extra maximum health adds a lasting benefit to an action otherwise valued for immediate recovery. It can make repeated Rest choices more attractive, but the card upgrade you pass still has a cost. Compare the current health preview, the specific upgrade and the fights before the next recovery rather than resting automatically whenever the relic is present.
Miniature Tent changes the tradeoff by allowing multiple available campfire actions. When Rest and Smith can both be chosen, you no longer need to give up the upgrade simply to activate the Humidifier’s Rest benefit.
Route planning also matters. A maximum-health bonus attached to several upcoming camps has more chances to contribute than one reached after most of the route is complete. Do not count hypothetical camps the chosen path cannot visit. The rest-site relic guide compares this trigger with entry healing, extra opening energy and boss-only healing.
