feat: workflow graph system — blocks 1-20 complete checkpoint

Full graph-based workflow execution engine with:
- WorkflowGraphRuntime with two-phase dispatch (collect → fire Celery tasks)
- Node registry with contract validation, socket types, execution kinds
- WorkflowRuntimeServices: preflight, context resolution, shadow-mode A/B
- WorkflowRouter: CRUD + dispatch/preflight/run-history API endpoints
- OutputTypeContracts: workflow binding, rollout-mode resolution
- Admin router: output-type workflow binding endpoints
- Frontend: complete workflow editor with drag-drop canvas, node inspector,
  module bundles, reference bundles, preflight panel, validation banner,
  authoring guidance, blueprint templates, shadow/rollout gate UI
- Tests: comprehensive coverage for all workflow modules
- Docs: NODE_CONTRACT_AUDIT and VALIDATION_ERROR_INVENTORY

All 20 blocks from NEXT_20_BLOCK_BATCH_PLAN completed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tests/domains/test_workflow_runtime_services.py

@@ -581,6 +581,32 @@ def test_prepare_order_line_render_context_skips_closed_orders(sync_session, tmp
     assert line.render_status == "cancelled"
 
 
+def test_prepare_order_line_render_context_allows_completed_rerender_for_workflow_editor(
+    sync_session,
+    tmp_path,
+    monkeypatch,
+):
+    from app.config import settings
+
+    monkeypatch.setattr(settings, "upload_dir", str(tmp_path / "uploads"))
+    line = _seed_order_line_graph(sync_session, tmp_path)
+    line.order.status = OrderStatus.completed
+    sync_session.commit()
+
+    result = prepare_order_line_render_context(
+        sync_session,
+        str(line.id),
+        persist_state=False,
+        allow_completed_order_rerender=True,
+    )
+    sync_session.refresh(line)
+
+    assert result.status == "ready"
+    assert result.reason is None
+    assert result.is_ready is True
+    assert line.render_status == "pending"
+
+
 def test_build_order_line_render_invocation_applies_output_and_line_overrides(tmp_path):
     step_path = tmp_path / "parts" / "bearing.step"
     step_path.parent.mkdir(parents=True, exist_ok=True)