Jepsen-style operation history recorder.

A history is a sequence of :invoke events (operations starting) paired with :ok / :fail / :info completion events. It's the raw input for consistency checkers like Lockstep.Checker.Linearizable.

Recording

Each operation has three lifecycle events:

• invoke — a process announces it's starting an operation
• ok — the operation completed and the caller knows the result
• fail — the operation explicitly didn't apply (returned an error the caller can interpret as "no change")
• info — the operation's outcome is unknown (caller crashed, timed out, lost the connection mid-call). Linearizability checkers must consider that the op MIGHT or MIGHT NOT have applied.

Quick example

history = Lockstep.History.start_link!()

# Concurrent workers issuing reads/writes
for i <- 1..3 do
  Lockstep.spawn(fn ->
    Lockstep.History.op(history, :write, i, fn ->
      Register.put(reg, i)
    end)
  end)
end

# ... wait for them ...

events = Lockstep.History.events(history)

{:ok, _info} =
  Lockstep.Checker.Linearizable.check(events, Lockstep.Model.Register)

Order

Events are indexed in the order they reach the recorder. Under Lockstep's deterministic controller this is also the real-time order — every invoke/ok call is a sync point routed through the controller, so the strategy controls when each event is recorded relative to others.