Engine performance and hygiene backlog

[krwg]

Summary

Incremental index, cache metrics, dead code, parser edges.

Target milestone: 2.8.5
Work branch: 2.8.5/issue-9-engine-hygiene

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Problem

Backlog: incremental index updates; embedding vector cache on index rows; FIFO cache metrics; dead shouldCandidatePassFastPath; guard string title; nested parens in OR parser; document onnxruntime-node peer dep.

Expected behavior

Tracked improvements for post-2.8.5 engine hardening.

Suggested approach

Implement incrementally; one PR per sub-item linked to this issue.

Files / areas

• lib/engine.js
• lib/tokenize.js
• lib/embeddings.js

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Acceptance criteria

• Sub-items checked off in issue comments as shipped

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Metadata

Field	Value
Priority	P2
Milestone	2.8.5
Branch	2.8.5/issue-9-engine-hygiene