/export shows duplicate "Session Started (codex)" entries

[nathanschram]

Bug

/export after a Codex run produces markdown with two consecutive "Session Started (codex)" sections, suggesting a duplicate StartedEvent is being recorded.

Reproduction

1. Send a prompt to the Codex engine chat (e.g. read /nonexistent/file)
2. Wait for completion
3. Send /export
4. Export output:

# Session Export: 019d186d-1db3-7d81-8ff6-6d9868b0e942
Exported: 2026-03-23 02:03 UTC

**Usage:** 9229 in / 187 out tokens

---

## Session Started (codex)
Model: Codex

- ▸ turn started
## Session Started (codex)
Model: Codex

- ▸ turn started

## ✓ Completed
...

Expected

Only one "Session Started" section per session in the export.

Context

• This may be caused by the Codex runner emitting two StartedEvents — one from thread.started and another from resume token matching
• Or the export recorder may be capturing events from multiple runs in the same thread without deduplication
• The duplicate appears to be an exact copy (same model, same "turn started" action)

Affected files

• src/untether/runners/codex.py — may emit duplicate StartedEvent on resume
• src/untether/telegram/commands/export.py — session event recording / deduplication

Version

v0.35.0rc11 — found during Codex integration testing