Bulk-update deal phase for one or more pairings. Valid phases: 0_prospecting, 1_contact, 1_initial_contact, 2_nda, 2_valuation, 4_ioi, 4_loi, 5_dd, 6_negotiation, 7_closing, 8_closed, 9_abandoned. MUTUAL CONSENT: a phase change is two-sided. When the caller identifies itself as one of the two parties (session_id of the pairing's buyer or seller), the change is NOT applied — it raises a pending confirmation request addressed to the counterparty, who confirms or dismisses it via POST /api/pairings/phase-request. Until then the pairing is locked: the phase stays visible but no further change is accepted, from either side or from any unattributed caller (the batch loop included). The lock is NOT open-ended: an unanswered request lapses automatically after the consent TTL (default 14 days, CONSENT_REQUEST_TTL_DAYS) and the pairing unlocks where it was. A caller that is not a party of the pairing (no session_id: Arnold's batch loop, the deal editor, a manual fix) applies directly — there is no one to ask — and is still blocked by a live request. Response reports three buckets: updated (applied now), requested (raised for confirmation, with request_id/to_phase/counterparty_session) and blocked (reason awaiting_confirmation).