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>

frontend/src/__tests__/components/workflowModuleBundles.test.ts

@@ -160,6 +160,25 @@ const definitions: WorkflowNodeDefinition[] = [
     artifact_roles_consumed: [],
     legacy_source: 'legacy.notify',
   },
+  {
+    step: 'export_blend',
+    label: 'Export Blend',
+    family: 'order_line',
+    module_key: 'media.export_blend',
+    category: 'output',
+    description: 'Export blend.',
+    node_type: 'outputNode',
+    icon: 'download',
+    defaults: {},
+    fields: [],
+    execution_kind: 'bridge',
+    legacy_compatible: true,
+    input_contract: { context: 'order_line', requires: ['render_template'] },
+    output_contract: { context: 'order_line', provides: ['blend_asset'] },
+    artifact_roles_produced: [],
+    artifact_roles_consumed: [],
+    legacy_source: 'legacy.export_blend',
+  },
 ]
 
 const cadDefinitions: WorkflowNodeDefinition[] = [
@@ -302,12 +321,18 @@ describe('workflowModuleBundles', () => {
   test('exposes family-scoped bundles when required steps exist', () => {
     const bundles = getWorkflowModuleBundles(definitions, 'order_line')
 
-    expect(bundles.map(bundle => bundle.id)).toEqual(['still_render_core', 'output_publish_notify'])
+    expect(bundles.map(bundle => bundle.id)).toEqual([
+      'scene_prep_core',
+      'materials_core',
+      'still_render_core',
+      'output_publish_notify',
+      'blend_export_publish',
+    ])
   })
 
-  test('creates a connected bundle insertion graph for still-render authoring', () => {
+  test('creates a connected bundle insertion graph for scene-prep authoring', () => {
     const insertion = createWorkflowModuleBundleInsertion({
-      bundleId: 'still_render_core',
+      bundleId: 'scene_prep_core',
       graphFamily: 'order_line',
       nodeDefinitionsByStep: Object.fromEntries(definitions.map(definition => [definition.step, definition])),
       existingNodes: [],
@@ -317,22 +342,44 @@ describe('workflowModuleBundles', () => {
     expect(insertion.ok).toBe(true)
     if (!insertion.ok) return
 
-    expect(insertion.nodes).toHaveLength(6)
-    expect(insertion.edges).toHaveLength(5)
+    expect(insertion.nodes).toHaveLength(3)
+    expect(insertion.edges).toHaveLength(2)
     expect(insertion.nodes[0].position).toEqual({ x: 200, y: 320 })
     expect(insertion.nodes[1].position).toEqual({ x: 420, y: 320 })
     expect(insertion.nodes[0].data).toMatchObject({ step: 'order_line_setup', label: 'Order Line Setup' })
-    expect(insertion.nodes[5].data).toMatchObject({ step: 'blender_still', label: 'Blender Still' })
+    expect(insertion.nodes[2].data).toMatchObject({ step: 'glb_bbox', label: 'Compute Bounding Box' })
     expect(insertion.edges[0]).toMatchObject({
       source: insertion.nodes[0].id,
       target: insertion.nodes[1].id,
     })
   })
 
+  test('creates a single-node still-render module for stage-level insertion', () => {
+    const insertion = createWorkflowModuleBundleInsertion({
+      bundleId: 'still_render_core',
+      graphFamily: 'order_line',
+      nodeDefinitionsByStep: Object.fromEntries(definitions.map(definition => [definition.step, definition])),
+      existingNodes: [],
+      preferredPosition: { x: 640, y: 180 },
+    })
+
+    expect(insertion.ok).toBe(true)
+    if (!insertion.ok) return
+
+    expect(insertion.nodes).toHaveLength(1)
+    expect(insertion.edges).toHaveLength(0)
+    expect(insertion.nodes[0].position).toEqual({ x: 640, y: 180 })
+    expect(insertion.nodes[0].data).toMatchObject({ step: 'blender_still', label: 'Blender Still' })
+  })
+
   test('exposes full reference paths for complete non-legacy authoring flows', () => {
     const bundles = getWorkflowReferenceBundles(definitions, 'order_line')
 
-    expect(bundles.map(bundle => bundle.id)).toEqual(['still_render_reference'])
+    expect(bundles.map(bundle => bundle.id)).toEqual([
+      'still_render_reference',
+      'still_render_alpha_reference',
+      'still_render_blend_reference',
+    ])
   })
 
   test('creates the canonical still-render reference graph with branched edges', () => {
@@ -354,7 +401,13 @@ describe('workflowModuleBundles', () => {
     expect(insertion.nodes[5].data).toMatchObject({
       step: 'blender_still',
       label: 'Still Render',
-      params: { use_custom_render_settings: true },
+      params: {
+        use_custom_render_settings: false,
+        render_engine: 'cycles',
+        samples: 256,
+        width: 1920,
+        height: 1080,
+      },
     })
     expect(insertion.edges).toEqual(
       expect.arrayContaining([
@@ -386,12 +439,13 @@ describe('workflowModuleBundles', () => {
     expect(insertion.ok).toBe(true)
     if (!insertion.ok) return
 
-    expect(insertion.nodes).toHaveLength(8)
-    expect(insertion.edges).toHaveLength(7)
+    expect(insertion.nodes).toHaveLength(9)
+    expect(insertion.edges).toHaveLength(9)
     expect(insertion.nodes.map(node => node.data.step)).toEqual([
       'resolve_step_path',
       'occ_object_extract',
       'occ_glb_export',
+      'glb_bbox',
       'stl_cache_generate',
       'blender_render',
       'threejs_render',
@@ -402,11 +456,15 @@ describe('workflowModuleBundles', () => {
       expect.arrayContaining([
         expect.objectContaining({
           source: insertion.nodes[2].id,
-          target: insertion.nodes[4].id,
+          target: insertion.nodes[5].id,
         }),
         expect.objectContaining({
           source: insertion.nodes[2].id,
-          target: insertion.nodes[5].id,
+          target: insertion.nodes[6].id,
+        }),
+        expect.objectContaining({
+          source: insertion.nodes[3].id,
+          target: insertion.nodes[6].id,
         }),
       ]),
     )