## Release v0.51.255 — Release HW (stage-r3)
Backend hardening — single PR.
### Fixed
| PR | Author | Fix |
|----|--------|-----|
| #3561 | @rodboev | Turn journal (crash-recovery backbone) writes **pid-scoped shards** (`{sid}~{pid}.jsonl`) instead of one shared `{sid}.jsonl`, so concurrent processes (e.g. a self-restart overlap) can't interleave-corrupt large JSON lines. `read_turn_journal` merges all shards + the legacy file and sorts by `created_at` — recovery unchanged, backward-compatible. |
### Gate
- Full pytest suite: **7593 passed, 0 failed**
- ruff: CLEAN · 18 turn-journal tests pass
- Codex (regression): **SAFE TO SHIP** — verified legacy+shard merge (no data loss on upgrade), `~` separator can't collide with a session id, the cross-shard `created_at` sort doesn't break recovery (it derives state by timestamp; stream lookup keys by unique `stream_id`), and no reader/writer bypasses `_journal_path`.
- *Non-blocking note:* old `{sid}~{oldpid}.jsonl` shards aren't pruned, so the journal dir can grow across restarts — storage hygiene, not a core-flow regression. Worth a follow-up cleanup (e.g. drop shards with no live pid on session delete).
Co-authored-by: rodboev <rodboev@users.noreply.github.com>
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