CBCL: Safe Self-Extending Agent Communication

TL;DR

CBCL is a formally verified agent communication language that safely supports runtime dialect extensions within a deterministic context-free language framework, ensuring safe, bounded, and extensible agent interactions.

Contribution

The paper introduces CBCL, a safe, extensible agent communication language with formal safety guarantees, implemented and verified in Lean 4 and Rust.

Findings

CBCL enforces safety invariants preventing unbounded expansion.

The language supports domain-specific dialect extensions as first-class messages.

Formal verification ensures the safety and correctness of the language implementation.

Abstract

Agent communication languages (ACLs) enable heterogeneous agents to share knowledge and coordinate across diverse domains. This diversity demands extensibility, but expressive extension mechanisms can push the input language beyond the complexity classes where full validation is tractable. We present CBCL (Common Business Communication Language), an agent communication language that constrains all messages, including runtime language extensions, to the deterministic context-free language (DCFL) class. CBCL allows agents to define, transmit, and adopt domain-specific "dialect" extensions as first-class messages; three safety invariants (R1--R3), machine-checked in Lean 4 and enforced in a Rust reference implementation, prevent unbounded expansion, applying declared resource limits, and preserving core vocabulary. We formalize the language and its safety properties in Lean 4, implement a reference parser and dialect engine in Rust with property-based and differential tests, and extract a verified parser binary. Our results demonstrate that homoiconic protocol design, where extension definitions share the same representation as ordinary messages, can be made provably safe. As autonomous agents increasingly extend their own communication capabilities, formally bounding what they can express to each other is a precondition for oversight.