Native subagent reports to unrelated fork via cross-thread messaging instead of its recorded parent

Summary

A native subagent spawned by thread A sent a progress report to thread B, a user-created fork of A with a different active task. B then responded to that unrelated report.

The sender explicitly supplied B's ID to mcp__codex_app__send_message_to_thread. This is not evidence that the transport delivered to the wrong requested ID. It is an observed parent-routing/tool-selection failure, with a possible tool-discovery or runtime contribution that remains unconfirmed.

Environment

• Codex Desktop on macOS.
• Affected fork's session metadata records bundled CLI 0.154.0-alpha.6.2.
• Native collaboration subagents; implementation worker spawned with fork_turns: "all".
• Code-mode tool orchestration via functions.exec; Codex app thread-management tools also available.
• Custom orchestration guidance is present. The currently inspected guidance explicitly distinguishes native subagent reporting from cross-task messaging; its exact incident-time contents have not been established.
• Exact Desktop About version and effective worker model are not established by this report.

Observed sequence (2026-09-14, UTC)

Thread IDs and business content are replaced with A/B/W below.

1. 05:07:06: B is created as a fork of A. Session metadata records forked_from_id: A. B is subsequently used for a different task.
2. 06:36:58: While handling that different task, B attempts collaboration.interrupt_agent for an agent from A's inherited history. It gets live agent path /root/<historical-worker> not found. This suggests confusion between inherited history and live team membership, not proof that the fork owns A's agents.
3. 07:06:38: A spawns native worker W. W's session metadata records:

   {
     "source": {
       "subagent": {
         "thread_spawn": {
           "parent_thread_id": "A",
           "depth": 1,
           "agent_path": "/root/renewal_model_integration",
           "agent_role": "worker"
         }
       }
     }
   }
   

4. 07:06:51: W searches ALL_TOOLS for send_message|collaboration|agent. Its runtime instructions explicitly say collaboration tools are direct calls and are absent from functions.exec's tools.* namespace. They also state that its final response is delivered to its parent.
5. 07:17:45: W calls mcp__codex_app__list_threads({limit:50}).
6. 07:17:54: W explicitly calls:

   await tools.mcp__codex_app__send_message_to_thread({
     threadId: "B", // not recorded parent A
     prompt: "<implementation progress report>"
   });
   

7. B records an incoming codex_delegation with source_thread_id: W and the implementation report. B replies to that report at 07:18:02, despite its active subject being unrelated.

These observations come from read-only inspection of the parent, fork, and worker rollout records. No synthetic reproduction has been attempted.

Expected behavior

• A native worker should report to its immediate spawning coordinator through native messaging or its final response.
• Parent identity should be unambiguous and should not require discovery through the user-facing task list.
• If native progress messaging is unavailable, the worker should fall back to its native final response, not infer a destination from related/forked chats.
• A fork should not treat inherited agent references as current live team ownership.
• Cross-task messages from native workers should require an explicitly assigned destination/purpose, or otherwise have a guardrail against accidental unrelated-thread sends.

Impact

An unrelated task is resumed and its context contaminated by a worker update. The intended coordinator may miss the update. This creates a risk of scope confusion; this report does not establish unauthorized external writes or business-data corruption resulting from the misplaced message.

Uncertainty / investigation request

The immediate wrong-ID selection is confirmed. The logs inspected do not prove that native collaboration messaging was actually unavailable to W; absence from ALL_TOOLS is not proof of absence from direct tool declarations. Please investigate whether this is model/tool-selection behavior alone or whether worker tool exposure, parent-identity presentation, or fork-context handling contributes.

Useful regression coverage would include a native worker whose parent has a user-created sibling fork, a missing/ambiguous progress-message capability, and a fork containing historical subagent references.

Privacy

No raw conversations, business data, account identifiers, private paths, credentials, or original thread IDs are included. A/B/W are placeholders. This report deliberately separates confirmed routing behavior from unverified runtime hypotheses.

Start with the parent, fork, and worker rollout records, including session metadata and the ALL_TOOLS inspection, then trace the native collaboration and mcp__codex_app__send_message_to_thread entry points. No source files or tests are named in the report. Done means establishing whether parent identity, tool exposure, or fork handling contributes and adding regression coverage for a sibling fork, missing or ambiguous messaging, and historical subagent references.