Iter-Coroutine + Base/Runtime Migration

Refactor sync+async modules to eliminate duplication using the iter-coroutine pattern. This skill covers the full migration workflow: identifying candidates, structuring internal modules, writing transport-agnostic business logic, and wiring up sync/async public APIs.

When to use

• A module has parallel sync and async implementations with duplicated logic.
• You're adding a new feature that needs both sync and async public APIs.
• You're refactoring an existing feature to use the shared HTTP transport layer.

Core principles