Set revoke_requested=true on the authenticated user's delegation for the
required party_id. This does not delete the row, clear its CID, change its
lifecycle status, or unlink the wallet. The engine performs actual revocation.
Both trading and RFQ delegations use this endpoint, including owned delegations
for previously linked parties. No client user_id or status is accepted.

An already-set flag returns the same 202 acknowledgement without another audit
or timestamp update. Each false-to-true change is audited as
delegation.revoke_requested. 202 is not confirmation of completed revocation.
GET /api/trading/delegation continues to report engine-owned lifecycle state
and omits revoked or expired rows once the engine updates them.

Revoking the currently linked trading party's delegation requires no open
orders and no active allocations; otherwise it returns HTTP 400
delegation_revocation_blocked with missing_steps: cancel_orders and/or
withdraw_allocations, and the flag is not set. RFQ and previously linked
parties are not subject to these checks.

Available in both API modes with the existing full-session, MFA, rate-limit,
killswitch and access-mode restrictions. Withdraw-only accounts cannot call it.