Mint a fresh test-type v2 conversation bound to an agent or team

conv_* replacement for the retired POST /v1/runtime/test-chat.

Mints a session_type="test" Conversation on the api channel with a throwaway end_user_id (no identity-graph node — the test discriminator suppresses memory sync, summary generation, and identity writes). The dashboard "Try this …" panel then drives turns via POST /v2/conversations/{id}/turns/stream passing the returned id.

Binds to exactly one of a single Assistant (agent_id) or a Team (team_id + optional team_revision_id); the request schema enforces that XOR. Either way the bound entity is resolved + org-scoped BEFORE the conversation is created (get_agent_for_runtime / get_team_for_org both raise 404 for a missing or cross-org id), so a bare test row can never bind to another org's agent/team.

For a team, team_revision_id defaults to the team's active_revision_id when omitted; bootstrap_team_conversation resolves the roster and pins bound_revisions at bind. No first greeting: the legacy endpoint emitted none, so there is nothing to replicate here.