CHW-4124 OrgSlugExists

Default message: A workspace with this name already exists. Try a different name.
HTTP status: 409 (client)

Problem. NO LONGER EMITTED. Sign-up used to answer this code, with the colliding slug, when the workspace name resolved to a slug another live org already held. It now allocates the next free suffix silently (acme taken becomes acme-2) and the sign-up succeeds. Cause. Telling an unauthenticated caller that a slug was taken was a customer-enumeration oracle for a security vendor: probe acme, learn Acme is a customer. The workspace name the caller chose is kept; only the derived slug, which sign-up never shows them, is suffixed. Fix. No caller action — sign-up no longer fails for this reason. This code stays registered so that a rolling deploy where an older pod still emits it remains documented and this page does not disappear; a client that still branches on it should retry the same sign-up rather than prompting for a new workspace name. Administrator-driven org creation and rename still report a taken slug — see CHW-4208. HTTP 409.