Specify and version additional event information provided by Hookshot

So that clients can rely on the information actually being there when rendering custom tile representations in clients.

No files, tests, or entry points are named. Start by tracing the event payload used for custom tile representations and reviewing the client-facing contract that needs additional information and versioning. Done means the event data is explicitly specified, versioned, and reliable for clients to render those representations.

Written by the indexing model from the issue text.