Decompose pipeline runner orchestration

internal/framework/pipeline/checkpoint.go

@@ -112,6 +112,30 @@ func requireReusableCheckpoint(policy CheckpointExecutionPolicy, stepID, laneID
 	return nil
 }
 
+// resolveCheckpointDecision applies runner policy and canonical payload
+// validation at the single point where a stage's observable decision is made.
+func resolveCheckpointDecision(output *RunOutput, loader CheckpointLoader, policy CheckpointExecutionPolicy, stage ModuleStage, stepID, laneID, moduleKey string, decision CheckpointDecision, codec artifactCodecEntry, artifacts []CheckpointArtifact) (CheckpointDecision, error) {
+	decision = forceCheckpointDecision(policy, stepID, laneID, decision)
+	if err := requireReusableCheckpoint(policy, stepID, laneID, decision); err != nil {
+		return decision, err
+	}
+	if decision.Reused {
+		for _, artifact := range artifacts {
+			if _, _, err := decodeCanonicalCheckpointArtifact(codec, artifact); err != nil {
+				decision = CheckpointDecision{Category: "executed", ReasonCode: "artifact_not_canonical", Detail: "stored " + string(stage) + " artifact failed canonical codec validation", Reason: string(stage) + " artifact checkpoint is not canonical"}
+				break
+			}
+		}
+	}
+	if err := requireReusableCheckpoint(policy, stepID, laneID, decision); err != nil {
+		return decision, err
+	}
+	if output != nil {
+		recordCheckpointEvent(output, loader, string(stage), stepID, laneID, moduleKey, decision)
+	}
+	return decision, nil
+}
+
 type SourceCheckpoint struct {
 	Document *source.SourceDocument
 }