fix(js): avoid precision loss in negative varint64 fast path - #3992
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chaokunyang
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Aug 29, 2026
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Why?
zigzag is computed in double precision, so any negative value with magnitude above 2^52 rounds to an even zigzag and decodes as positive: -4503599627370497n round-trips as +4503599627370496n. Also reachable through writeSliInt64.
What does this PR do?
the writeVarInt64 fast path now requires v >= -(2^52) in both the number and safe-range bigint branches; anything more negative falls through to the exact bigint zigzag (v << 1n) ^ (v >> 63n). writeSliInt64 is fixed too since its big-long path delegates here. A short comment on the new constant records the invariant.
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yes/noyes, I included a completed AI Contribution Checklist in this PR description and the requiredAI Usage Disclosure.yes, my PR description includes the requiredai_reviewsummary and screenshot evidence or equivalent persisted links of the final clean AI review results from both fresh reviewers described inAI_POLICY.md, the Fory-guided reviewer and the independent general reviewer, on the current PR diff or current HEAD after the latest code changes.Does this PR introduce any user-facing change?
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