codex: spawned subagent's first response is not counted when its token_count event repeats #1970

What happened?

ccusage codex does not count a spawned subagent's first response when Codex writes that response's token_count event twice, less than a second apart.

• If the subagent has only one response, the whole subagent is missing from codex session and codex daily.
• If it has more responses, only the first is missing.

There is no error or warning, so the totals are silently too low.

I found this in my own ~/.codex/sessions. One subagent rollout had one response followed by two identical token_count events, 150 ms apart, and its 15,870 tokens were missing from my reports. I maintain a small tool that runs ccusage for usage receipts, and its own cross-check flagged the gap.

I think the cause is the replay fallback for thread_spawn rollouts (#1218, #1501). The repeated event looks like a replay burst, so the real first response is skipped as replayed parent history. Codex re-emitting unchanged token_count events is already known from #876 and #1288.

Steps to reproduce

1. Save these 4 lines as $CODEX_HOME/sessions/2026/01/05/rollout-2026-01-05T15-00-00-22222222-0000-4000-8000-000000000000.jsonl:

{"timestamp":"2026-01-05T15:00:00.000Z","type":"session_meta","payload":{"id":"22222222-0000-4000-8000-000000000000","timestamp":"2026-01-05T15:00:00.000Z","cwd":"/tmp/x","source":{"subagent":{"thread_spawn":{"parent_thread_id":"11111111-0000-4000-8000-000000000000","depth":1}}}}}
{"timestamp":"2026-01-05T15:00:01.000Z","type":"turn_context","payload":{"model":"gpt-5"}}
{"timestamp":"2026-01-05T15:00:02.000Z","type":"event_msg","payload":{"type":"token_count","info":{"total_token_usage":{"input_tokens":1000,"cached_input_tokens":400,"output_tokens":10,"reasoning_output_tokens":0,"total_tokens":1010},"last_token_usage":{"input_tokens":1000,"cached_input_tokens":400,"output_tokens":10,"reasoning_output_tokens":0,"total_tokens":1010}}}}
{"timestamp":"2026-01-05T15:00:02.150Z","type":"event_msg","payload":{"type":"token_count","info":{"total_token_usage":{"input_tokens":1000,"cached_input_tokens":400,"output_tokens":10,"reasoning_output_tokens":0,"total_tokens":1010},"last_token_usage":{"input_tokens":1000,"cached_input_tokens":400,"output_tokens":10,"reasoning_output_tokens":0,"total_tokens":1010}}}}

2. Run ccusage codex daily --json --offline -z UTC.
3. Result: totalTokens is 0 and there are no days.

Other results with the same file:

Expected behavior

The subagent's response is counted once: 1010 tokens. A repeated token_count event with an unchanged total should be treated as a duplicate, not as replayed history.

Version

20.0.38 and 20.0.44 (latest). Same result on both.