Begin an OAuth connect for a chat-requested MCP server

The one-time setup token, and a client credential only if the server demanded one.

There is no address, no audience and no label here, and their absence is the design. Those three were frozen when Patricia minted the link, under the requester's authority and, for a team server, under an approval bound to them. The console's own start accepts an address and an audience from the browser and defaults a new connection to team, so a body that carried them would let a personal request come back as a team connection with every console rule satisfied.

client_id and client_secret are the same pair the console's credentials step collects, INHERITED from :class:services.mcp_oauth.PastedClientCredentialFields rather than restated, so a secret never arriving without an id, a blank id being refused, and an id being trimmed while a secret keeps every byte are one rule with one implementation. OAuthStartBody inherits the same base. They are the SECOND call of one connect, sent after this route answered that the server's sign-in service will not register Patricia on its own.

Where to send the person, and what the ceremony they are leaving for will come back as.