Bond of Words

A minor form of the geas spell, often used by nobility, merchants, and adversaries to create binding contracts.    Two or more willing creatures in range agree to perform some action (usually an exchange of some sort) within a specified time and under specified conditions.    For example, "I give you 500 gold pieces and you release the hostages unharmed within 24 hours."

All parties to the spell must be willing, must understand the terms in the same way, and must not be under duress.   All participants must intend to complete their part of the agreement at the time of casting.  The contract cannot cause physical harm or death to any participant.  If any of those conditions do not hold, the spell fails (and all participants know that).

Once cast, the spell binds all participants until the conditions are met.   Any side not meeting their obligation will have their maximum hit points reduced by 1d4/day and take 2d6 psychic damage at dawn each day.   The penalties do not happen until the party is in noncompliance:  a clause like "you will return the borrowed item after a year" does not trigger penalties during the specified year. 

The spell binds the intent and spirit of the agreement, not its literal words.      A wish can dissolve a Bond.   The Bond is also dissolved immediately if the terms become unfulfillable due to circumstances outside the control of either party, or if either party's maximim hp is reduced to 0 by the penalties.

Once the Bond is fulfilled, any lost maximum hp are restored.   If the bond is dissolved, a greater restoration or similar can restore lost maximum hp.