Finalize artifact workflow documentation

docs/internal/overview.md

@@ -43,6 +43,14 @@ Narratio-level contracts; external transport and SDK details remain in
 adapters. The normative rules for these relationships remain in
 [Architecture](../policy/architecture.md).
 
+Pipeline execution and `session plan` share the same inclusive contiguous-range
+model. Planning clones session state and applies selected-stage transitions and
+resume validation in memory; it does not create invocation state or initialize
+stage-execution adapters. Command configuration loading can still retrieve a
+missing session file through configured remote storage. Analyze planning
+additionally exposes the artifact closure's targets, prerequisite rebuilds,
+execution order, and current reuse.
+
 ## Pipeline Stage Set
 
 The implemented canonical order is: