chore(deps): fix the dependency audit (multidict; fsspec CVE ignored pending sentence-transformers 5)

[wongk]

Why

Dependency audit fails on every PR again (first seen on #40): two advisories published this week, against multidict and fsspec.

What

• multidict 6.7.1 → 6.9.1 (CVE-2026-104874). The only package that changes in uv.lock.
• fsspec stays at 2026.4.0; CVE-2026-104851 is ignored in the audit, with an lc-debt note and a removal condition.
  • The fix (fsspec 2026.6.0) is reachable only through datasets 5.1, which needs huggingface-hub ≥ 1.31. The semantic extra's sentence-transformers < 5 needs transformers < 5, which needs huggingface-hub < 1.0. uv can only satisfy fsspec 2026.6+ by dropping datasets to 2.14.4.
  • The flaw is template injection in fsspec's ReferenceFileSystem when opening a Kerchunk reference document. Nothing in src/, benchmarks/ or integrations/ imports fsspec or opens a reference filesystem; datasets is used only by the SWE-bench benchmark loader (benchmarks/codebench/swebench_pro_data.py).
  • The ignore comes out with the move to sentence-transformers 5 / transformers 5, which is a separate, larger change to the semantic search stack.

Verification

• The CI audit command run locally against the new lock: No known vulnerabilities found, 9 ignored.
• uv lock --check passes; the lock diff is multidict only.