Agent Action that locally deletes a stored Xochi Mandate envelope.

v1 has no server revoke endpoint -- Xochi's KV budget counter for this envelope remains until expires_at per the agent-auth design doc (2026-04-27). When Xochi does revoke or exhaust a mandate, it answers a protected call with 410 Gone; the outbound plugin (Raxol.Payments.Req.Mandate) prunes the local envelope on that response, so a server-side revocation converges locally without this Action.