ACM-68000 signals for listed issuers

get_signal retrieves the signal for a specific listed security, while list_signals is a reference catalog of the four signal codes and reserved codes. The purposes are distinct, though 'list_signals' could be misread as enumerating issuers' signals rather than the code definitions; the descriptions resolve this.

Both tools follow the same verb_noun snake_case pattern (get_signal, list_signals), and the verb choice matches the semantics of retrieval vs. enumeration.

Two tools is thin for a signal-serving domain: only single-security lookup plus a static code catalog. No batch or bulk retrieval means agents must call per security, which feels under-provisioned rather than well-scoped.

Core read path (lookup by identifier) and code reference are covered, but there is no reverse lookup (e.g., which issuers are ACM-403 halted or ACM-451 filing), no batch retrieval, and no way to resolve an ambiguous bare ticker within a single call beyond the candidate list in the error.