Exact Store replay
==================

``MuscleAction.actuator_setpoints`` is the historical **proposed** action,
captured before actuator post-filters.  It remains available for compatibility.
``MuscleAction.applied_actuator_setpoints`` is the final post-filter action and
therefore the action returned to the ``SimulationController`` for environment
execution and used by exact Store-backed replay when present.

An ordinary replay definition remains backwards compatible.  Exact sequential
pretraining opts in to immutable source selection and validation::

  replay:
    - agent: teacher
      experiment_run: teacher-run
      instance: immutable-instance-uid
      phase: 1
      mode: train
      strict: true
      repeat: 1

Strict replay requires selected rows to contain an applied action, worker and
monotonic decision identity, reward, and explicit ``terminated``/``truncated``
flags consistent with ``done``.  It rejects duplicate/non-monotonic decisions,
missing fields, empty selections, and more than one worker in a source.  Rows
are ordered by worker, episode, decision index, then Store ID; each episode is
placed in its own Memory shard so successors never cross an episode boundary.
All sequential Store replay rejects a source containing more than one worker:
interleaving independent worker trajectories would otherwise fabricate
adjacency.  Strict mode additionally requires exact fields and raises setup
errors; non-strict mode retains its best-effort legacy proposed-action fallback.

The columns are nullable by design.  Existing databases are upgraded through
Alembic revision ``d21a0b4c6e7``; legacy replay continues to use the historical
proposed-action field on a best-effort basis.