Closed-World Resolution Against Tool Hallucination in LLM Agents
The resolver replaces nothing in the existing pipeline; it adds a training-free pre-gate check (tool registry membership plus argument signature validation) that rejects calls to nonexistent tools or with undeclared arguments before any causal or security gate runs, since a hallucinated call is by construction outside what a gate decided. Its cost is negligible compute and latency (a lookup and a schema check), with the engineering burden of maintaining an accurate, versioned tool registry and correctly handling merged MCP namespaces where name collisions and shadowing create surfaces a single registry cannot express. It fails on the one irreducible residue: calls to real tools with borrowed arguments that are schema-indistinguishable from valid calls, which requires downstream gating or execution checks rather than closed-world resolution.
