Thin, sync-read JSON artifact loader for the future vendored
llm-security-commons subtree, modeled on signature-scanner.mjs's
loadRules()/loadCustomRules() pair: process-cached, graceful-empty
fallback on any read/parse error, and policy-extensible via a
`commons.root` policy value (mirrors sig.custom_rules_path).
Unit-tested now against a local fixture — Phase 4 (commons repo
creation, gated on the operator creating the Forgejo remote) hasn't
run yet, so the default `shared/` vendor path doesn't exist in this
checkout. That "not vendored yet" case is itself asserted: the loader
must degrade to the caller's fallback, not crash.
Not wired to any consumer yet (that's Phase 5 step 4, table-by-table
behind the golden gate). No CLI/hook/scanner-visible behaviour exists
to document. Golden baseline unchanged; full suite 2063/2063 (2053 +
10 new).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QAYkRaBXT6tmWXTQAi1ZBg
