Phase 0: prove Tantivy Directory semantics and the minimum rocksdb-js bridge

[kylebernhardy]

Outcome

Retire the highest-risk assumptions before broad Rocks adapter implementation.

Acceptance criteria

• Exercise open_write, immediate readability, repeated flush, writer continuation, immutable open FileSlice prefixes, termination, delete-while-open, locks, watch, and atomic_write behavior from pinned Tantivy 0.26.1.
• Prototype against current rocksdb-js APIs and document precisely why any native bridge operation is required.
• Compare WAL-enabled publication with WAL-disabled objects plus a durability barrier.
• Measure JavaScript callback, copy, point-read, and database-wide flush costs.
• Produce a go/no-go decision and the minimum capability table for Epic: Provide the minimum native storage capabilities required by fulltext rocksdb-js#831.
• Do not commit to pinned reads, MultiGet, or target-CF flush unless correctness or measured performance requires them.

Comment generated by kAIle (Codex GPT-5)