PDG query surface with GitNexus

Expert knowledge for the pdg_query MCP tool and the control/data-dependence edges it reads — the opt-in --pdg program-dependence layers. Read this before touching gitnexus/src/mcp/local/local-backend.ts (_pdgQueryImpl) or the pdg_query tool def, or when explaining a pdg_query result.

When to Use

• "Under what condition does this statement run?" (guarding predicates).
• "Where does this variable flow inside the function?" (def→use).
• Guard-clause discovery (early-return guards — subsumes the #559 heuristic).
• Extending or reviewing pdg_query / the CDG / REACHING_DEF read path.
• Debugging an empty or surprising pdg_query result.

The layered substrate (build order)

pdg_query runs on the same graph taint runs on. Each layer is opt-in behind --pdg; a default analyze run records none of them (byte-identical).