Confirmed from raw Codex session logs on macOS.

In the local session JSONL, each assistant message is recorded twice in sequence:

event_msg with payload.type: "agent_message"
response_item with payload.type: "message", role: "assistant"

I checked four sessions for the same repo on 2026-03-07 and all show a strict 1:1 duplicate-pair pattern:

session A: 17 duplicate pairs
session B: 21 duplicate pairs
session C: 4 duplicate pairs
session D: 6 duplicate pairs

So this does not look like the model independently generating the same text twice. It looks like the UI/log consumer is rendering both record types when stream assistant messages is enabled.

Environment details from the session metadata:

Codex CLI 0.111.0
observed with session sources exec and vscode

If useful, I can provide a small repro parser against the JSONL format, but the key signal is that each duplicated visible message corresponds to one agent_message record immediately followed by one assistant response_item with identical text.

Responses duplicate when Stream assistant messages is on #349

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