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/app/domains/rendering/workflow_config_utils.py

@@ -19,7 +19,13 @@ _PRESET_TYPES = {
 }
 
 _EXECUTION_MODES = {"legacy", "graph", "shadow"}
-_WORKFLOW_BLUEPRINTS = {"cad_intake", "order_rendering", "still_graph_reference"}
+_WORKFLOW_BLUEPRINTS = {
+    "cad_intake",
+    "order_rendering",
+    "still_graph_reference",
+    "still_graph_alpha_reference",
+    "still_graph_blend_reference",
+}
 _WORKFLOW_STARTERS = {"cad_file", "order_line"}
 _WORKFLOW_STARTER_BLUEPRINTS = {
     "starter_cad_intake": "cad_file",
@@ -74,9 +80,16 @@ def _extract_render_params_from_nodes(nodes: list[dict[str, Any]], step: StepNam
     return {}
 
 
-def _build_order_line_still_graph_nodes(render_params: dict[str, Any]) -> tuple[list[dict[str, Any]], list[dict[str, Any]]]:
+def _build_order_line_still_graph_nodes(
+    render_params: dict[str, Any],
+    *,
+    transparent_bg: bool | None = None,
+    include_blend_export: bool = False,
+) -> tuple[list[dict[str, Any]], list[dict[str, Any]]]:
     graph_render_params = deepcopy(render_params)
     graph_render_params.setdefault("use_custom_render_settings", False)
+    if transparent_bg is not None:
+        graph_render_params["transparent_bg"] = transparent_bg
 
     nodes = [
         _make_node("setup", StepName.ORDER_LINE_SETUP, 0, 160, label="Order Line Setup"),
@@ -108,6 +121,29 @@ def _build_order_line_still_graph_nodes(render_params: dict[str, Any]) -> tuple[
         {"from": "render", "to": "output"},
         {"from": "render", "to": "notify"},
     ]
+    if include_blend_export:
+        nodes.extend(
+            [
+                _make_node("blend_export", StepName.EXPORT_BLEND, 920, 360, label="Export Blend"),
+                _make_node(
+                    "save_blend",
+                    StepName.OUTPUT_SAVE,
+                    1160,
+                    320,
+                    params={"expected_artifact_role": "blend_export"},
+                    label="Save Blend Output",
+                ),
+                _make_node("notify_blend", StepName.NOTIFY, 1160, 420, label="Notify Blend Export"),
+            ]
+        )
+        edges.extend(
+            [
+                {"from": "setup", "to": "blend_export"},
+                {"from": "template", "to": "blend_export"},
+                {"from": "blend_export", "to": "save_blend"},
+                {"from": "blend_export", "to": "notify_blend"},
+            ]
+        )
     return nodes, edges
 
 
@@ -329,6 +365,16 @@ def build_workflow_blueprint_config(blueprint: str) -> dict[str, Any]:
         nodes, edges = _build_order_line_still_graph_nodes(
             {"render_engine": "cycles", "samples": 256, "width": 1920, "height": 1080}
         )
+    elif blueprint == "still_graph_alpha_reference":
+        nodes, edges = _build_order_line_still_graph_nodes(
+            {"render_engine": "cycles", "samples": 256, "width": 1920, "height": 1080},
+            transparent_bg=True,
+        )
+    elif blueprint == "still_graph_blend_reference":
+        nodes, edges = _build_order_line_still_graph_nodes(
+            {"render_engine": "cycles", "samples": 256, "width": 1920, "height": 1080},
+            include_blend_export=True,
+        )
 
     return {
         "version": 1,
@@ -336,7 +382,7 @@ def build_workflow_blueprint_config(blueprint: str) -> dict[str, Any]:
         "edges": edges,
         "ui": {
             "preset": "custom",
-            "execution_mode": "graph" if blueprint == "still_graph_reference" else "legacy",
+            "execution_mode": "graph" if blueprint.startswith("still_graph_") else "legacy",
             "family": "cad_file" if blueprint == "cad_intake" else "order_line",
             "blueprint": blueprint,
         },