Proposal: experimental local cross-session messaging via UDS

What variant of Codex are you using?

CLI

What feature would you like to see?

Background

Currently, Codex sessions are isolated. Multiple CLI instances on the same machine cannot communicate or coordinate.

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Proposal

Introduce an experimental, local-only cross-session messaging mechanism using Unix Domain Sockets (UDS).

Goal:

One session can send a text message to another, and the receiving agent sees it directly in its conversation context.

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Scope (Stage 0)

Keep the first version minimal:

• Local machine only (UDS)
• Plain text messages only
• No persistence
• Top-level sessions only
• No file transfer or structured payloads

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User-facing behavior

Two new tools:

• list_sessions — discover other sessions
• send_session_message(target, message) — send a message

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Behavior

When a message is received:

• It is injected into the target session’s conversation context
• The agent sees it as a normal input on the next turn and can respond

Questions

Would appreciate feedback on:

1. Is injecting messages into the conversation context acceptable?
2. Should this reuse existing InterAgentCommunication, or be separate?
3. Is UDS a reasonable transport for a first step?

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Next step

If this direction makes sense, I can follow up with a small, feature-flagged PR implementing Stage 0.

Additional information

_No response_