更新0.1.5-rc.1后大部分会话打不开

[shubingdev]

历史加载失败：failed to observe session "session-xxx": assistant/message 93534 chunk provenance is not one complete ordered attempt; source v0 artifact remains unchanged

[xiaoshenming]

This is the converter's chunk-attempt check: an assistant/message must cite either nothing or exactly the complete ordered run of assistant/chunk events for the same (turn, step) since the last attempt.

dsh-session-surgeon detects it as v0-chunk-provenance and repairs by citing the chunk seqs already on disk (empty citation when there is no run) — no seq is invented. Verified against the released 0.1.5-rc.1 sessionFormatV0ToV1 stage: refused before repair, clean migration after; --apply writes .bak.<utc> first. Details in #6151.