What problem does this feature address?

When a dispute is created, mediators have a range of tools to modify an offer. For non-disputed offers, those tools don't appear and the offer state is stuck without direct database intervention.

Describe a solution

Allow mediators to join any offer except for offers they are sending or receiving.

Examples of similar features

The existing dispute tools.

Mediators can join offers that they did not send or receive. However, there are several side effects.

• When the mediator joins the offer, there is an Offer Failed notice at the top, regardless of the status of the offer.
• This creates an entry on the dispute page
• The offer will appear in mediation at the top of the sender and receiver's offer page until the mediator clicks Resolved.
• Changing the failed reasons may not be useful and it's the main function available
• The other power is reset to pending / accepted, but other options needed