System-only chat requests mapped the system message to instructions and left
input=[], which OpenAI's Responses API rejects (it also rejects input=""). When
no other messages are present, carry the system message as a role:"system" input
item (single copy, correct role) instead of leaving input empty. Mirrors the
existing handling of non-string system content. Fixes Open WebUI new-conversation
failures on mode:responses Codex models.
Co-authored-by: Cursor <cursoragent@cursor.com>
milan-berri
273855b4e2