Create a live-session grant

Creates a short-lived read-only access grant for the current live session. Use this endpoint to mint a short-lived read-only URL for embedding or opening the current payer-channel session. `GET /live-session` is side-effect-free; it does not mint bearer capabilities. The grant is scoped to the current prior authorization and live session. Opening the grant URL validates and audits the grant, then redirects to the runtime provider's read-only live view. Interactive access is not available here; create a manual handoff before minting an interactive handoff grant. ## Returns Returns a `LiveSessionAccessGrant`.