v8.3.0

Fixed — dynamic StageNode returns no longer mutate the shared built chart (backlog #7)

• Traverser-local dynamic-patch overlay. Phase 4 of FlowchartTraverser
  (dynamic StageNode-return handling) used to write the dynamic shape
  DIRECTLY onto the built chart's shared node objects —
  isSubflowRoot/subflowId/subflowName/subflowMountOptions (dynamic
  subflow), children + nextNodeSelector (dynamic fork), and next
  (restored after the visit — the only field that was). A chart built once
  is a shared artifact: the mutation leaked one run's dynamic graph into
  every later run of the same built chart (a fresh executor would re-execute
  stale dynamic children with the PREVIOUS run's closed-over args, or
  misclassify a stage as a subflow mount and skip its continuation) and
  raced concurrent executors sharing one chart. Phase 4 now writes patches
  into a per-traverser dynamicPatches: Map<nodeId, DynamicNodePatch>
  overlay that dies with the run — the built graph is never touched. Every
  engine read of the patched fields goes through effective-value accessors
  (effChildren/effSelector/effIsSubflowRoot/effSubflowId/effNode),
  and helper executors (NodeResolver loop-target DFS, SubflowExecutor,
  ChildrenExecutor) receive the effective node view instead of reading
  stale built fields. Dynamic next stays a local routed through
  ContinuationResolver — the save/restore dance on the shared node is
  gone. Fast path preserved: charts with no dynamic returns pay one
  size === 0 check per read. Zero behavior change for any single run;
  structureManager.updateDynamic* observability events fire exactly as
  before.