Ensure `events.jsonl` honors inherited file-size limits

## Summary

The Copilot CLI persists session events to:

`~/.copilot/session-state//events.jsonl`

The CLI inherits the hosting process’s file-size limit. During sufficiently long
sessions, `events.jsonl` reaches that limit and the next persistence write fails:

> I/O error: File too large (os error 27)

This emits `SDK_SESSION_ERROR(persistence)` and fails the active turn.

## Request

Please ensure that `events.jsonl` remains within the file-size limit inherited by
the Copilot CLI while preserving supported session persistence and resume behavior.

If this behavior is owned by the bundled CLI runtime rather than the SDK wrappers,
please route the issue to the appropriate owner.

## Environment

- SDK: `github-copilot-sdk==1.0.7`
- Bundled CLI: 1.0.71
- Host file-size limit: 50 MB
- Platform: Linux container
- Error: `EFBIG` / `os error 27`

## Acceptance criteria

- `events.jsonl` does not exceed the inherited file-size limit.
- Long-running sessions do not fail with EFBIG due to event-log growth.
- Persisted sessions remain resumable with their expected state.

## Impact

Observed in production across real user conversations, causing repeated
Service-class turn failures.

## Reference

Internal tracking: https://microsoft.ghe.com/bic/mcs-dracarys/issues/7127

Start by tracing persistence for ~/.copilot/session-state//events.jsonl and the path that emits SDK_SESSION_ERROR(persistence). Check how the inherited 50 MB file-size limit and EFBIG failure affect writes, then verify that long-running sessions stay within the limit and remain resumable without persistence errors.

索引モデルが issue の本文から書いたものです。