diff --git a/modules/gems/func.js b/modules/gems/func.js
index 33f334bf..94fe8bb0 100644
--- a/modules/gems/func.js
+++ b/modules/gems/func.js
@@ -1 +1,18 @@
-export const NOOP = () => {};
\ No newline at end of file
+export const NOOP = () => {};
+
+export function createFunctionList() {
+  const fnList = [];
+  const add = fn => fnList.push(fn);
+  const call = () => {
+    fnList.forEach(fn => {
+      try {
+        fn(); 
+      } catch(e) {
+        console.error(e);
+      }
+    });
+  };
+  return {
+    add, call
+  }
+}
\ No newline at end of file
diff --git a/web/app/cad/craft/wizard/components/Wizard.jsx b/web/app/cad/craft/wizard/components/Wizard.jsx
index bdbe5ec4..80fbc880 100644
--- a/web/app/cad/craft/wizard/components/Wizard.jsx
+++ b/web/app/cad/craft/wizard/components/Wizard.jsx
@@ -8,27 +8,26 @@ import ls from './Wizard.less';
 import CadError from '../../../../utils/errors';
 import {FormContext} from './form/Form';
 import connect from 'ui/connect';
-import mapContext from 'ui/mapContext';
+import {combine} from 'lstream';
 
-@connect(streams => streams.wizard.workingRequest)
-@mapContext(ctx => ({
-  updateParam: (name, value) => {
-    let workingRequest$ = ctx.streams.wizard.workingRequest;
-    if (workingRequest$.value.params && workingRequest$.value.type) {
-      workingRequest$.mutate(data => {
-        data.params[name] = value;
-        data.state.activeParam = name; 
-      })
-    }
-  },
-  setActiveParam: name => ctx.streams.wizard.workingRequest.mutate(data => data.state && (data.state.activeParam = name))
-}))
+@connect((streams, props) => combine(props.context.workingRequest$, props.context.state$)
+  .map(([workingRequest, state]) => ({
+    ...workingRequest,
+    activeParam: state.activeParam
+  })))
 export default class Wizard extends React.Component {
 
   state = {
     hasError: false,
   };
 
+  updateParam = (name, value) => {
+    this.props.context.updateParams(params => params[name] = value);
+  };
+
+  setActiveParam = param => {
+    this.props.context.updateState(state => state.activeParam = param);
+  };
 
   componentDidCatch() {
     this.setState({hasInternalError: true});
@@ -39,24 +38,16 @@ export default class Wizard extends React.Component {
       return <span>operation error</span>;
     }
 
-    let {left, type, params, state, resolveOperation, updateParam, setActiveParam} = this.props;
-    if (!type) {
-      return null;
-    }
-
-    let operation = resolveOperation(type);
-    if (!operation) {
-      console.error('unknown operation ' + type);
-      return null;
-    }
+    let {left, type, params, state, context} = this.props;
+    let operation = context.operation;
 
     let title = (operation.label || type).toUpperCase();
 
     let formContext = {
       data: params,
-      activeParam: state.activeParam,
-      setActiveParam,
-      updateParam
+      activeParam: this.props.activeParam,
+      setActiveParam: this.setActiveParam,
+      updateParam: this.updateParam
     };
 
     let Form = operation.form;
@@ -127,7 +118,7 @@ export default class Wizard extends React.Component {
       let {code, userMessage, kind} = error;
       printError = !code;
       if (CadError.ALGORITMTHM_ERROR_KINDS.includes(kind)) {
-        stateUpdate.algorithmError = true
+        stateUpdate.algorithmError = true;
       }
       if (code && kind === CadError.KIND.INTERNAL_ERROR) {
         console.warn('Operation Error Code: ' + code);
diff --git a/web/app/cad/craft/wizard/components/WizardManager.jsx b/web/app/cad/craft/wizard/components/WizardManager.jsx
index 43bba870..8f6e4d11 100644
--- a/web/app/cad/craft/wizard/components/WizardManager.jsx
+++ b/web/app/cad/craft/wizard/components/WizardManager.jsx
@@ -3,23 +3,21 @@ import Wizard from './Wizard';
 import connect from 'ui/connect';
 import decoratorChain from 'ui/decoratorChain';
 import mapContext from 'ui/mapContext';
-import {finishHistoryEditing} from '../../craftHistoryUtils';
 
-function WizardManager({type, changingHistory, resolve, cancel, stepHistory, insertOperation, cancelHistoryEdit, applyWorkingRequest}) {
-  if (!type) {
+function WizardManager({wizardContext, type, changingHistory, cancel, cancelHistoryEdit, applyWorkingRequest}) {
+  if (!wizardContext) {
     return null;
   }
-  return <Wizard resolveOperation={resolve}
+  return <Wizard key={wizardContext.ID}
+                 context={wizardContext}
                  onCancel={changingHistory ? cancelHistoryEdit : cancel}
                  onOK={applyWorkingRequest} />
 }
 
 export default decoratorChain(
-  connect(streams => streams.wizard.effectiveOperation),
-  mapContext((ctx, props) => ({
+  connect(streams => streams.wizard.wizardContext.map(wizardContext => ({wizardContext}))),
+  mapContext(ctx => ({
     cancel: ctx.services.wizard.cancel,
-    resolve: type => ctx.services.operation.get(type),
-    cancelHistoryEdit: () => ctx.streams.craft.modifications.update(modifications => finishHistoryEditing(modifications)),
     applyWorkingRequest: ctx.services.wizard.applyWorkingRequest 
   }))
 )
diff --git a/web/app/cad/craft/wizard/wizardPlugin.js b/web/app/cad/craft/wizard/wizardPlugin.js
index 9ae104d6..7b766ca7 100644
--- a/web/app/cad/craft/wizard/wizardPlugin.js
+++ b/web/app/cad/craft/wizard/wizardPlugin.js
@@ -1,7 +1,8 @@
-import {stream, state} from 'lstream';
+import {state} from 'lstream';
 import initializeBySchema from '../intializeBySchema';
 import {clone, EMPTY_OBJECT} from 'gems/objects';
 import materializeParams from '../materializeParams';
+import {createFunctionList} from 'gems/func';
 
 export function activate(ctx) {
 
@@ -46,12 +47,12 @@ export function activate(ctx) {
     gotoEditHistoryModeIfNeeded(mod);
   });
 
-  streams.wizard.workingRequestChanged = stream();
-  
-  streams.wizard.workingRequest = streams.wizard.effectiveOperation.map(opRequest => {
-    let request = EMPTY_OBJECT;
+  streams.wizard.wizardContext = streams.wizard.effectiveOperation.map(opRequest => {
+    let wizCtx = null;
     if (opRequest.type) {
+      
       let operation = ctx.services.operation.get(opRequest.type);
+
       let params;
       if (opRequest.changingHistory) {
         params = clone(opRequest.params)
@@ -61,34 +62,45 @@ export function activate(ctx) {
           applyOverrides(params, opRequest.initialOverrides);
         }
       }
-      request = {
+
+      let workingRequest$ = state({
         type: opRequest.type,
-        params,
-        state: {}
-      };
-    }
-    streams.wizard.workingRequestChanged.next(request);
-    return request
-  }).remember(EMPTY_OBJECT);
-
-  streams.wizard.materializedWorkingRequest = streams.wizard.workingRequest.map(req => {
-    if (req.type) {
-      let operation = ctx.services.operation.get(req.type);
-      let params = {};
-      let errors = [];
-      materializeParams(ctx.services, req.params, operation.schema, params, errors, []);
-      if (errors.length !== 0) {
-        console.log(errors);
-        return INVALID_REQUEST;
-      }
-      return {
-        type: req.type,
         params
+      });
+      
+      let materializedWorkingRequest$ = workingRequest$.map(req => {
+        let params = {};
+        let errors = [];
+        materializeParams(ctx.services, req.params, operation.schema, params, errors, []);
+        if (errors.length !== 0) {
+          console.log(errors);
+          return INVALID_REQUEST;
+        }
+        return {
+          type: req.type,
+          params
+        };
+      }).filter(r => r !== INVALID_REQUEST).remember();
+      const state$ = state({});
+      const updateParams = mutator => workingRequest$.mutate(data => mutator(data.params));
+      const updateState = mutator => state$.mutate(state => mutator(state));
+      const disposerList = createFunctionList();
+      wizCtx = {
+        workingRequest$, materializedWorkingRequest$, state$, operation, updateParams, updateState,
+        addDisposer: disposerList.add,
+        dispose: disposerList.call,
+        ID: ++REQUEST_COUNTER,
       };
     }
-    return EMPTY_OBJECT;
-  }).filter(r => r !== INVALID_REQUEST).remember();
+    return wizCtx;
+  }).remember(null);
 
+  streams.wizard.wizardContext.pairwise().attach(([oldContext, newContext]) => {
+    if (oldContext) {
+      oldContext.dispose();
+    } 
+  });
+  
   services.wizard = {
 
     open: (type, initialOverrides) => {
@@ -104,7 +116,7 @@ export function activate(ctx) {
     },
     
     applyWorkingRequest: () => {
-      let {type, params} = streams.wizard.workingRequest.value;
+      let {type, params} = streams.wizard.wizardContext.value.workingRequest$.value;
       let request = clone({type, params});
       if (streams.wizard.insertOperation.value.type) {
         ctx.services.craft.modify(request, () => streams.wizard.insertOperation.value = EMPTY_OBJECT);
@@ -119,4 +131,5 @@ function applyOverrides(params, initialOverrides) {
   Object.assign(params, initialOverrides);
 }
 
-const INVALID_REQUEST = {};
\ No newline at end of file
+const INVALID_REQUEST = {};
+let REQUEST_COUNTER = 0;
\ No newline at end of file
diff --git a/web/app/cad/craft/wizard/wizardSelectionPlugin.js b/web/app/cad/craft/wizard/wizardSelectionPlugin.js
index 1cddee32..f359f9b6 100644
--- a/web/app/cad/craft/wizard/wizardSelectionPlugin.js
+++ b/web/app/cad/craft/wizard/wizardSelectionPlugin.js
@@ -1,37 +1,34 @@
-import {DATUM, EDGE, FACE, SHELL, SKETCH_OBJECT} from '../../scene/entites';
+import {EDGE, FACE, SHELL, SKETCH_OBJECT} from '../../scene/entites';
 
 export function activate(ctx) {
-  const wizardPickHandler = createPickHandlerFromSchema(ctx);
-  
-  ctx.streams.wizard.workingRequestChanged.attach(({type, params}) => {
+  ctx.streams.wizard.wizardContext.attach(wizCtx => {
     ctx.services.marker.clear();
-    if (type) {
+    if (wizCtx) {
+      const wizardPickHandler = createPickHandlerFromSchema(wizCtx);
       ctx.services.pickControl.setPickHandler(wizardPickHandler);
+      wizCtx.workingRequest$.attach(({type, params}) => {
+        const marker = ctx.services.marker;
+        marker.startSession();
+        let {schema, schemaIndex} = wizCtx.operation;
+        schemaIndex.entityParams.forEach(param => {
+          let color = schema[param].markColor;
+          let val = params[param];
+          let entity = schemaIndex.entitiesByParam[param];
+          if (Array.isArray(val)) {
+            val.forEach(id => marker.mark(entity, id, color));
+          } else {
+            if (val) {
+              marker.mark(entity, val, color);
+            }
+          }
+        });
+        marker.commit();
+      });
+
     } else {
       ctx.services.pickControl.setPickHandler(null);
     }
   });
-
-  ctx.streams.wizard.workingRequest.attach(({type, params}) => {
-    const marker = ctx.services.marker;
-    marker.startSession();
-    if (type && params) {
-      let {schema, schemaIndex} = ctx.services.operation.get(type);
-      schemaIndex.entityParams.forEach(param => {
-        let color = schema[param].markColor;
-        let val = params[param];
-        let entity = schemaIndex.entitiesByParam[param];
-        if (Array.isArray(val)) {
-          val.forEach(id => marker.mark(entity, id, color));
-        } else {
-          if (val) {
-            marker.mark(entity, val, color);
-          }
-        }
-      });
-    }
-    marker.commit();
-  });
 }
 
 const singleUpdater = (params, param, id) =>  params[param] = id;
@@ -45,11 +42,20 @@ const arrayUpdater = (params, param, id) =>  {
   }
 };
 
-function createPickHandlerFromSchema(ctx) {
+function createPickHandlerFromSchema(wizCtx) {
+  function update(paramsMutator, paramToMakeActive) {
+    wizCtx.updateParams(paramsMutator);
+    wizCtx.updateState(state => {
+      state.activeParam = paramToMakeActive;
+    });
+  }
   return model => {
     const modelType = model.TYPE;
-    const {type: opType, state, params} = ctx.streams.wizard.workingRequest.value;
-    let {schema, schemaIndex} = ctx.services.operation.get(opType);
+    
+    const params = wizCtx.workingRequest$.value.params;
+    const state = wizCtx.state$.value;
+    
+    let {schema, schemaIndex} = wizCtx.operation;
     const {entitiesByType, entitiesByParam, entityParams} = schemaIndex;
 
     const activeMd = state.activeParam && schema[state.activeParam];
@@ -58,15 +64,14 @@ function createPickHandlerFromSchema(ctx) {
     function select(param, entity, md, id) {
       const updater = md.type === 'array' ? arrayUpdater : singleUpdater;
       let paramToMakeActive = getNextActiveParam(param, md);
-      ctx.streams.wizard.workingRequest.mutate(r => {
-        updater(r.params, param, id);
-        r.state.activeParam = paramToMakeActive;
-      });
+      update(params => {
+        updater(params, param, id);
+      }, paramToMakeActive);
     }
 
     function getNextActiveParam(currParam, currMd) {
       if (currMd.type !== 'array') {
-        let entityGroup = entitiesByType[currMd.type];
+        let entityGroup = entitiesByType[activeEntity];
         if (entityGroup) {
           const index = entityGroup.indexOf(currParam);
           const nextIndex = (index + 1) % entityGroup.length;
@@ -93,23 +98,20 @@ function createPickHandlerFromSchema(ctx) {
       for (let param of entityParams) {
         let val = params[param];
         if (val === id) {
-          ctx.streams.wizard.workingRequest.mutate(r => {
-            r.params[param] = undefined;
-            r.state.activeParam = param;
-          });
+          update(params => {
+            params[param] = undefined;
+          }, param);
           return true;
         } else if (Array.isArray(val)) {
           let index = val.indexOf(id);
           if (index !== -1) {
-            ctx.streams.wizard.workingRequest.mutate(r => {
-              r.params[param].splice(index, 1);
-              r.state.activeParam = param;
-            });
+            update(params => {
+              params[param].splice(index, 1)
+            }, param);
             return true;
           }
         }
       }
-      
     }
 
     if (deselectIfNeeded(model.id)) {
@@ -142,12 +144,6 @@ function createPickHandlerFromSchema(ctx) {
       } else {
         selectToFirst(EDGE, model.id);
       }
-    } else if (modelType === DATUM) {
-      if (activeEntity === DATUM) {
-        selectActive(model.id);
-      } else {
-        selectToFirst(DATUM, model.id);
-      }
     }
     return false;
   };
diff --git a/web/app/cad/preview/previewPlugin.js b/web/app/cad/preview/previewPlugin.js
index 78344a8a..e96d03c5 100644
--- a/web/app/cad/preview/previewPlugin.js
+++ b/web/app/cad/preview/previewPlugin.js
@@ -3,46 +3,29 @@ import {createPreviewer} from './scenePreviewer';
 export function activate(ctx) {
   let {streams, services} = ctx;
   
-  const updateParams = mutator => streams.wizard.workingRequest.mutate(data => mutator(data.params));
-  
-  let previewContext = {
-    operation: null,
-    previewer: null
-  };
-
-  streams.wizard.materializedWorkingRequest.attach(({type, params}) => {
-    if (!type) {
-      if (previewContext.previewer) {
-        previewContext.previewer.dispose();
-        previewContext.previewer = null;
-        previewContext.operation = null;
-        ctx.services.viewer.requestRender();
-      }
+  streams.wizard.wizardContext.attach(wizCtx => {
+    if (!wizCtx) {
       return;
     }
-    if (type !== previewContext.operation) {
-      if (previewContext.previewer != null) {
-        previewContext.previewer.dispose();
+    let {operation, materializedWorkingRequest$} = wizCtx; 
+    if (operation.previewGeomProvider || operation.previewer) {
+      let previewer = null;
+      materializedWorkingRequest$.attach(({type, params}) => {
+        if (previewer === null) {
+          if (operation.previewGeomProvider) {
+            previewer = createPreviewer(operation.previewGeomProvider, services, params);
+          } else if (operation.previewer) {
+            previewer = operation.previewer(ctx, params, wizCtx.updateParams);
+          }
+          wizCtx.addDisposer(() => {
+            previewer.dispose();
+            ctx.services.viewer.requestRender();
+          });
+        } else {
+          previewer.update(params);
+        }
         ctx.services.viewer.requestRender();
-        previewContext.previewer = null;
-      }
-      let operation = services.operation.get(type);
-
-      if (operation.previewGeomProvider) {
-        previewContext.previewer = createPreviewer(operation.previewGeomProvider, services, params);
-        ctx.services.viewer.requestRender();
-      } else if (operation.previewer) {
-        previewContext.previewer = operation.previewer(ctx, params, updateParams);
-        ctx.services.viewer.requestRender();
-      } else {
-        previewContext.previewer = null;
-      }
-      previewContext.operation = type;
-    } else {
-      if (previewContext.previewer) {
-        previewContext.previewer.update(params);
-        ctx.services.viewer.requestRender();
-      }
+      });
     }
   });
 }
\ No newline at end of file
diff --git a/web/app/cad/scene/selectionMarker/markerPlugin.js b/web/app/cad/scene/selectionMarker/markerPlugin.js
index 028d6259..aa45bcc8 100644
--- a/web/app/cad/scene/selectionMarker/markerPlugin.js
+++ b/web/app/cad/scene/selectionMarker/markerPlugin.js
@@ -21,6 +21,9 @@ function createMarker(findEntity, requestRender) {
 
   function doMark(entity, id, color) {
     let mObj = findEntity(entity, id);
+    if (!mObj) {
+      throw 'illegal state';
+    }
     marked.set(id, mObj);
     mObj.ext.view && mObj.ext.view.mark(color);
   }