feat: version rollout weight updates

Track a monotonic policy version across optimizer steps, scheduler updates, and rollout results. Serialize synchronous generation with weight acknowledgements and invalidate reusable prefix KV entries so cached samples remain attributable to the behavior policy that generated them.

astrai/trainer/strategy.py

@@ -239,6 +239,12 @@ class BaseStrategy(ABC):
         """Inject a :class:`RolloutRunner` to enable online rollout mode."""
         self._rollout_runner = runner
 
+    @property
+    def policy_version(self) -> Optional[int]:
+        if self._rollout_runner is None:
+            return None
+        return self._rollout_runner.policy_version
+
     def prepare_from_rollout(self, result: RolloutResult) -> Dict[str, Tensor]:
         """Map a :class:`RolloutResult` to the batch layout expected by
         :meth:`compute_loss`.
@@ -275,6 +281,7 @@ class BaseStrategy(ABC):
     def on_optimizer_step(self):
         """Advance online rollout state after a successful optimizer step."""
         if self._rollout_runner is not None:
+            self._rollout_runner.update_weights(self.policy_version + 1)
             self._rollout_runner.step()
 
     def __call__(self, batch: Dict[str, Tensor]) -> LossOutput: