Custom names for group chat channels

[johnpooch]

Goal

Let players give a private group channel a custom name — set optionally when creating the channel and editable afterward by the channel's creator — while always surfacing the real participants so a misleading name cannot actually deceive anyone. This is a small bit of fun players intuitively expect, and decoupling the display name from the participant list keeps it consistent with the spirit of Diplomacy.

Definition of done

• Channel records its creator, and only that player can name or rename the channel.
• When creating a private channel, the player may optionally provide a custom name; they can rename it later via a dedicated endpoint. Non-creators cannot rename it, and attempts are rejected.
• When no custom name is set, the channel continues to display the auto-generated participant list (current behaviour is preserved).
• The real participants (nations) are always shown explicitly alongside any custom name, in both the channel list and the channel header, so a custom name can never hide who is actually in the channel.
• Public channels remain unaffected and cannot be renamed.

Context

Today Channel.name is auto-generated by joining sorted nation names (e.g. England, France) and is read-only in the serializer; there is no creator/owner field on the model. Supporting custom names therefore requires storing the display name separately from the derived participant list so both can be shown at once.

This came out of a community discussion. The concern raised was that free-form channel names could be used to mislead — e.g. naming a channel after nations who aren't actually in it to trick someone into revealing information. The agreed resolution is not to forbid custom names but to always display the true participants alongside the name, which is why explicit participant visibility is part of the definition of done rather than a nice-to-have.

Out of scope: renaming public channels.