Protocol v3 (?) will add mandatory `version` parameter to `REST: Opaque Request`

[QuintinWillison]

Most of our client libraries advertise compliance with this feature as specified by RSC19.

ably/specification#89: Protocol v2 adds RSC19f, replacing RSC19a, fundamentally changing the way that this API is used.

I think this warrants a new feature node. Perhaps as a child of the existing node:

REST: Opaque Request: with Version

Or as a new sibling of the existing node, introducing deprecation of the existing node (a minor bump to this repository) or replacing it entirely (a major bump to this repository):

REST: Opaque Request with Version

Work on this issue will involve making that decision, so that this new feature node is made available to downstream SDK repositories to appear in their compliance manifests.

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-2847

[SimonWoolf]

We might also want to do a wider redesign of rest#request (which is currently very weird) at the same time as this, given we have to break the api anyway for this. CF discussion at ably/specification#103

[QuintinWillison]

I've modified the title of this issue to reflect the recent decision that this change will be separated from the no-connection-serial work (which is v2, making this a v3 change to the wire protocol). cc @SimonWoolf