FTS indexes built with with_position=True crash lance's optimize/compaction
on lancedb >= 0.32 when merging an unindexed tail (Max offset exceeds length
of values; upstream lance-format/lance#7653). The crash aborts optimize()
including version cleanup, so the index dir grows unbounded until the disk
fills. everos recall is OR-mode BM25 and never does phrase queries, so
positions are never read -- disabling is lossless.
- base: default with_position=False
- infra: migrate_fts_indexes() rebuilds pre-fix indexes once at startup + reclaims orphans
- cascade worker: count consecutive optimize failures, escalate warning->error
Fixes#335.
Co-authored-by: zhanghui <zhanghui@shanda.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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