Trace payload for {:trace, %__MODULE__{}} - emitted before any state is exited (docs/observability.md constraint 2's "exit set" row). indexes are the states to be exited (constraint 3, integer indexes), in exit order.

Two sites emit it, matching the two places this engine exits states: Statifier.Interpreter.ExitEntry.exit_states/2 over compute_exit_set's result, and Statifier.Interpreter.exit_interpreter/1 over the whole configuration at termination. Both are phase boundaries Appendix D names (exitStates and exitInterpreter compute the same statesToExit), so ADR-0012 item 2 asks for the row at both.

configuration is the full configuration (ADR-0005, ancestors included) as it stands after every state in indexes has left it, so a consumer can render the configuration per microstep without folding deltas. It is deliberately the only field taken from the post-exit state; macrostep/microstep/round are stamped from the state as it stood at the phase boundary the payload names, which is what keeps this payload an "exit set" marker rather than an after-the-fact report (test/fixtures/adr_judge/0012_trace_prestate_captured.diff is the sanctioned shape). At Statifier.Interpreter.exit_interpreter/1 the sweep empties the configuration, so configuration is MapSet.new() there - which is the true resulting configuration and not a missing value; Trace.Done.configuration, which carries the configuration as it stood at exit, is the payload that answers "what was active when the run ended".

Built with new/2, never a struct literal, so macrostep/microstep/ round are always stamped from the Statifier.MachineState at hand.