Codex subagent traces double-count inherited token history

[gregb122]

Summary

Codex child rollout files contain copied parent token history followed by the child's new work. Token Meter groups these files under the shared session_id and prices every token_count.last_token_usage row, so inherited history is counted repeatedly.

Tested against main at 79f1759d854c84ecda4858b3e350755bf765c894 on macOS.

Evidence

• At one fixed checkpoint, Token Meter displayed $2,503.041764 and 3.63B priced tokens.
• Removing only exact inherited prefixes and 39 adjacent duplicate snapshots produced $156.084712 and 200.91M priced tokens: 16.04× inflation.
• The checkpoint contained 54 physical traces for five logical tasks; 49 traces were children.
• token_meter/runtimes/codex.py:190-195 prefers the shared session_id as the source ID.
• token_meter/runtimes/codex.py:227-229 selects payload.session_id before the unique payload.id.
• token_meter/runtimes/codex.py:878-905 prices every token-count row without accounting for lineage.
• Related issue #2 covers duplicate Claude sources, but choosing one canonical Codex file would lose legitimate child work. Codex children require inherited-prefix removal.

Impact

Daily, session, model, and budget totals can be overstated by an order of magnitude when Codex uses multiple or nested subagents. Users may also interpret the API-equivalent estimate as actual subscription spend.

Suggested fix

1. Preserve separate physical trace ID, logical session ID, forked_from_id, and parent_thread_id fields.
2. For each child, remove only the longest exact token-event prefix shared with forked_from_id, falling back to parent_thread_id.
3. Compare model plus numeric last_token_usage fields and ignore timestamps because copied history is re-stamped.
4. After prefix removal, skip only adjacent events whose model, last_token_usage, and total_token_usage are all identical.
5. Continue pricing last_token_usage; do not price cumulative-total deltas.
6. Label Codex dollars as estimated public API equivalent.

Acceptance criteria

• Root, direct-child, and nested-child fixtures count inherited history once.
• Children without a resolvable exact prefix retain all events.
• Adjacent exact snapshots are removed only after lineage matching.
• Session, Daily, Models, and budget totals agree after correction.
• The reproduced checkpoint is approximately $156.08, not $2,503.04.

If accepted I can work on fixing this

[bhavsarpratik]

update: Fix in progress by @gregb122

[bhavsarpratik]

@gregb122 A fix was rolled out. Please check and close this if its resolved.