Set the signed-in human's own account preferences. Body {summary_opt_in: bool} and/or {sales_report: "off" | "daily" | "weekly" | "monthly", sales_report_scope: "own" | "workspace"} (the seller sales report, #594) and/or {signup_source: str | null} — the optional "How did you hear about us?" answer (collector/signup_source.py, #775): at most 200 characters, scrubbed before it is stored; "" skips the question, null removes an earlier answer. While AGENT_MDX_SIGNUP_SOURCE is off every value is refused with 403 signup_source_off (nothing is recorded) — except null for an account that still holds an answer, which removes it.

Session-only, like GET /auth/me: a ge_sess_ bearer from a sign-in. Machine tokens (admin / emit / read / unified) and library tokens are refused with 401 not_logged_in — consent to sending your session text to an LLM is a human's decision, never a token's. There is no user id in the path or body, so a caller can only ever change their OWN account.