[codex] Use background agent task auth for backend calls#18094

adrian-openai wants to merge 6 commits intodev/adrian/codex/agent-identity-use-assertion-splitopenai/codex:dev/adrian/codex/agent-identity-use-assertion-splitfrom

dev/adrian/codex/agent-identity-background-taskopenai/codex:dev/adrian/codex/agent-identity-background-taskCopy head branch name to clipboard