Correctness hardening: enable mypy untyped-body checks for discovery paths

[mark-e-deyoung]

Summary

Track deferred correctness work for Group C (static enforcement).

Problem

Mypy currently skips bodies of untyped functions in discovery paths, reducing static correctness guarantees in concurrency/network code.

Scope

• Enable mypy --check-untyped-defs for api/core/discovery.py.
• Add missing annotations and small refactors required to pass strict body checks.
• Evaluate phased expansion to other modules where untyped bodies remain.

Acceptance criteria

• Discovery module passes mypy with untyped-body checking enabled.
• CI includes this check without materially increasing runtime.
• Follow-up plan documented for broader adoption.

Notes

Deferred to keep runtime behavior changes and static-typing expansion decoupled.