lockstep

Use this skill when the user wants to find or verify concurrency bugs in BEAM code (Elixir, Erlang, Gleam) using Lockstep, the controlled-scheduling test framework. Triggers include: "test for races", "verify this is concurrency-safe", "find the schedule that causes this flaky test", "why does this fail occasionally", or any mention of GenServer/ETS/atomics race conditions.