Literature Search (shared toolchain)

This skill is not a loop — it is the literature-retrieval dependency several loops use for paper discovery and novelty checks. It bundles tools/lit_search.py (a stdlib-only entrypoint) and the tools/lit/ package: Semantic Scholar (S2) for semantic search + snippets + the citation graph and arXiv for full-text reads (the keyless core), plus optional OpenAlex, Perplexity Sonar (ask), and bgpt.pro (bgpt) when their keys are set. Every subcommand prints JSON; on a terminal failure it prints {"error","fallback"} and exits non-zero so the caller degrades to its built-in WebSearch/WebFetch. No installs, Python ≥3.9.

How a loop uses it