bug(debug): a Codex debug bundle can miss the latest prompt body

[Juliusolsson05]

Found by review C of #1332 (#372). The behavior predates that PR.

Expected

A debug bundle for a Codex session carries the latest request body (the prompt that produced the behavior being reported), as Claude bundles do through latest-request-body.json (#1273).

Actual

The bundle's proxy section is the last 5 MiB of proxy-events.jsonl (plus .1 after a rotation, #1332). A /v1/responses request followed by more than 5 MiB of response chunks or /v1/models refreshes has its body_b64 before the tail, so the bundle holds recent chunks but no prompt body.

Evidence

temp/review-1332/report-c.md finding 1. Line by line over the live corpus:

• Legacy format: in 40 of 65 Codex files with an inline body, the last body lies more than 5 MiB before EOF.
• Projected to the current base64 format: 10 of 65.

Codex has no latest-request-body.json sidecar.

Direction

Mirror Claude: have codex-headless's EventsMirror keep the newest request body in a sidecar next to the events file (or re-emit it after each rotation). readLatestRequestBody in proxyEventsReader.ts already appends a sidecar.

[Juliusolsson05]

Closed attempt: #1399 (branch kept; reopenable). It made a Codex debug bundle fall back from resume-<providerSessionId> to shell-<sessionId>. Review a (P1) showed that no search order over those two directory keys is correct:

• Resume first (as in fix(debug): a fresh session's debug bundle finds its own proxy run #1399): pane p1 starts fresh conversation T (shell-p1/R1); later pane p2 resumes T (resume-T/R2). Saving p1's bundle picks R2, which is p2's run and prompts.
• Shell first: a cold-recovered pane keeps its local id and would pick its own stale fresh-run dir.
• Newest of both: still picks p2's run in the case above.

proxyEventsReader matches directory names only; match: 'exact' means the segment string, not pane or process provenance. The real fix is a launch-time proxy run identity recorded per session: #1405. The #1399 tests (an assembler-level stub of readProxyEvents) and its manifest fields (requestedSessionKey, matchedSessionSegment, proxyRunDir) are reusable. The package half, codex-headless#70 (the latest request body kept beside the run), is independent.