Make every delegated context boundary explicit
Use when. You use Codex CLI or Desktop MultiAgentV2 from a long-lived or resumed parent that launches subagents.
Action. Upgrade is not a mitigation: issue #34061 reproduces through 0.144.6. In every V2 spawn_agent call, set "fork_turns":"none" when the task packet is self-contained; otherwise set a small positive string such as "3" and include missing requirements and artifact paths in message. Never omit the field: current source defaults omission to "all". For V1 use fork_context:false. Keep agents.max_depth=1 unless recursion is essential. Before unattended rollout, measure $CODEX_HOME/sessions, run one parent plus three children, then measure the delta and largest child JSONL. Do not delete existing history as part of this gate.
task packet → fork_turns: none or N → three-child canary → inspect captured calls and session growth → release or blockAcceptance check. Pass only if every captured V2 tool call carries none or the approved N; no child begins with an embedded parent session_meta; total session-store growth stays below a budget set before the canary; and repeating the canary grows roughly linearly, not by another copy of the parent per child. Any omitted or all fork, duplicated parent metadata, or superlinear growth blocks rollout.
#34061 contains privacy-safe filesystem counts and record-type byte totals from Codex 0.142.4–0.144.6: one resumed parent produced 2,393 child files totaling about 731.5 GiB. An independent Linux reproduction found 117.9 MB—99.72% of one child file—persisted before the child’s first actual turn. Codex main source confirms omission becomes all and legacy full-history loading includes stored history. Older issue #14981 had already identified the missing hard kill-switch.Caveat. none removes conversational context; a bounded N can also omit a required decision. Supply a destination-specific task packet and artifact references, then acceptance-test the child’s output. The report is strongest for legacy-history, long or resumed parents; ordinary paginated, short-lived sessions may grow far less. Codex still exposes no hard config switch that forbids full-history forks, so prompt or skill instructions are guidance, not tool-boundary enforcement.