List Assignable Account Managers

Who an organization's account manager can be set to.

Gated on orgs:read, deliberately NOT on admin:people:read. The only other principals roster is GET /api/platform/principals, which requires admin:people:read -- a grant an ACCOUNT MANAGER does not hold. Feeding the picker from there would have broken it for precisely the people who work on this page, the same way the AM column once showed them raw UUIDs.

SCOPED TO THE Account Manager ROLE (build task "flexible Actions menu + Organizations list", 2026-08-09) -- this used to return every active human (19), so both the Organizations list's account-manager FILTER and the "set account manager" picker in OrganizationFormModal offered people who do not do this job. Frederick's hand-created "Account Manager" role (migrations/0046_ticket_access_by_role.sql's own comment) is exactly the 2 real ones -- principal_roles/roles, the same membership registry.py's own role machinery reads everywhere else, not a second roster.

Returns names and ids only: enough to choose someone, and nothing about their access, contact details or employment.