diff --git a/modules/lstream/base.js b/modules/lstream/base.js
index 207690d7..ca189e76 100644
--- a/modules/lstream/base.js
+++ b/modules/lstream/base.js
@@ -14,8 +14,8 @@ export class StreamBase {
     return new PairwiseStream(this, first);
   }
 
-  scan(initAccumulator) {
-    return new ScanStream(this, initAccumulator);
+  scan(initAccumulator, scanFunc) {
+    return new ScanStream(this, initAccumulator, scanFunc);
   }
   
   remember(initialValue, usingStream) {
diff --git a/modules/lstream/index.d.ts b/modules/lstream/index.d.ts
index d9dedf3f..9f86a360 100644
--- a/modules/lstream/index.d.ts
+++ b/modules/lstream/index.d.ts
@@ -9,11 +9,11 @@ interface Stream<T> extends Observable<T> {
 
   filter(predicate: (T) => boolean): Stream<T>;
 
-  pairwise(first: T): Stream<[T, T]>;
+  pairwise(first?: T): Stream<[T, T]>;
 
-  scan(initAccumulator: any): Stream<any>;
+  scan<T>(seed: T, scanFn: (accum: T, current: T) => T): Stream<T>;
 
-  remember(initialValue: T, usingStream: any): StateStream<T>
+  remember(initialValue: T, usingStream?: any): StateStream<T>
 
   distinct(): Stream<T>;
 
@@ -42,7 +42,7 @@ export function stream<T>(): Emitter<T>;
 
 export function eventStream<T>(): Emitter<T>;
 
-export function combine(...streams: Stream<any>[]): Stream<any[]>;
+export function combine<T>(...streams: Stream<any>[]): Stream<T>;
 
 export function merge(...streams: Stream<any>[]): Stream<any>;
 
diff --git a/modules/lstream/scan.js b/modules/lstream/scan.js
index 10a3810c..c58c8af5 100644
--- a/modules/lstream/scan.js
+++ b/modules/lstream/scan.js
@@ -2,13 +2,17 @@ import {StreamBase} from './base';
 
 export class ScanStream extends StreamBase {
 
-  constructor(stream, initAccumulator) {
+  constructor(stream, seed, scanFunc) {
     super();
     this.stream = stream;
-    this.acc = initAccumulator;
+    this.value = seed;
+    this.scanFunc = scanFunc;
   }
 
   attach(observer) {
-    return this.stream.attach(v => this.acc = observer(this.acc, v));
+    return this.stream.attach(v => {
+      this.value = this.scanFunc(this.value, v);
+      observer(this.value);
+    });
   }
 }
diff --git a/modules/ui/components/GenericWizard.tsx b/modules/ui/components/GenericWizard.tsx
index 58f1a800..a9830d21 100644
--- a/modules/ui/components/GenericWizard.tsx
+++ b/modules/ui/components/GenericWizard.tsx
@@ -13,7 +13,8 @@ export function GenericWizard({topicId, title, left, className, children, onCanc
   left?: number,
   onCancel: () => any,
   onOK: () => any,
-  infoText: string
+  onKeyDown: (e) => any,
+  infoText: any
 } & WindowProps ) {
 
   return <Window initWidth={250}
diff --git a/modules/ui/components/controls/ComboBoxControl.jsx b/modules/ui/components/controls/ComboBoxControl.jsx
index 57541c9f..8b899772 100644
--- a/modules/ui/components/controls/ComboBoxControl.jsx
+++ b/modules/ui/components/controls/ComboBoxControl.jsx
@@ -3,8 +3,22 @@ import React from 'react';
 export default class ComboBoxControl extends React.Component {
   
   render() {
-    let {onChange, value, children} = this.props;
+    let {onChange, value, includeNonExistent, children} = this.props;
+    let nonExistent = null;
+    if (includeNonExistent) {
+      let needsInclusion = false;
+      React.Children.forEach(children, opt => {
+        if (opt.value === value) {
+          needsInclusion = false;
+        }
+      });
+      if (needsInclusion) {
+        nonExistent = <ComboBoxOption value={value}>{value ?  value+'' : '<empty>'}</ComboBoxOption>;
+      }
+    }
+
     return <select value={value} onChange={e => onChange(e.target.value)}>
+      {nonExistent}
       {children}
     </select>  
   }
diff --git a/modules/ui/errorBoundary.js b/modules/ui/errorBoundary.js
deleted file mode 100644
index 9f2d8da4..00000000
--- a/modules/ui/errorBoundary.js
+++ /dev/null
@@ -1,50 +0,0 @@
-import React from 'react';
-import context from 'context';
-
-export default function errorBoundary(message, fix, resetOn) {
-  return function(Comp) {
-    class ErrorBoundary extends React.Component {
-
-      state = {
-        hasError: false,
-        fixAttempt: false
-      };
-
-      componentDidCatch() {
-        this.setState({hasError: true});
-        if (!this.state.fixAttempt) {
-          if (fix) {
-            fix(this.props);
-            this.setState({hasError: false, fixAttempt: true});
-          }
-        }
-        if (resetOn) {
-          let stream = resetOn(context.streams);
-          if (stream) {
-            this.attcahing = true;
-            this.detacher = stream.attach(this.reset);
-            this.attcahing = false;
-          }
-        }
-      }
-
-      reset = () => {
-        if (this.attcahing) {
-          return;
-        }
-        this.setState({hasError: false, fixAttempt: false});
-        if (this.detacher) {
-          this.detacher();
-        }
-      };
-      
-      render() {
-        if (this.state.hasError) {
-          return message || null;
-        }
-        return <Comp {...this.props} />;
-      }
-    }
-    return ErrorBoundary;
-  }
-}
\ No newline at end of file
diff --git a/modules/ui/errorBoundary.tsx b/modules/ui/errorBoundary.tsx
new file mode 100644
index 00000000..692094d0
--- /dev/null
+++ b/modules/ui/errorBoundary.tsx
@@ -0,0 +1,40 @@
+import React from 'react';
+import context from 'context';
+import {Stream} from "lstream";
+import {useStream} from "ui/effects";
+
+type ErrorBoundaryProps = {
+  message: any;
+  children: any;
+};
+
+export function HealingErrorBoundary({resetOn, ...props}: ErrorBoundaryProps & {
+  resetOn: (ctx) => Stream<any>,
+}) {
+
+  const key = useStream(ctx => resetOn(ctx).scan(0, (acc, curr) => acc + curr));
+
+  return <ErrorBoundary key={key} {...props} />;
+}
+
+export class ErrorBoundary extends React.Component<ErrorBoundaryProps, {
+  hasError: boolean
+}> {
+
+  state = {
+    hasError: false,
+  };
+
+  componentDidCatch(error:Error, errorInfo:React.ErrorInfo) {
+    console.error(error);
+    this.setState({hasError: true});
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return this.props.message || null;
+    }
+    return this.props.children;
+  }
+}
+
diff --git a/package-lock.json b/package-lock.json
index f404c149..905437de 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -12,6 +12,7 @@
         "classnames": "2.2.5",
         "clipper-lib": "6.2.1",
         "earcut": "2.1.1",
+        "immer": "^9.0.12",
         "less": "^3.11.1",
         "libtess": "1.2.2",
         "lodash": "^4.17.15",
@@ -7512,6 +7513,15 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/immer": {
+      "version": "9.0.12",
+      "resolved": "https://registry.npmjs.org/immer/-/immer-9.0.12.tgz",
+      "integrity": "sha512-lk7UNmSbAukB5B6dh9fnh5D0bJTOFKxVg2cyJWTYrWRfhLrLMBquONcUs3aFq507hNoIZEDDh8lb8UtOizSMhA==",
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/immer"
+      }
+    },
     "node_modules/import-fresh": {
       "version": "3.2.1",
       "resolved": "https://registry.npmjs.org/import-fresh/-/import-fresh-3.2.1.tgz",
@@ -21428,6 +21438,11 @@
       "integrity": "sha1-Cd/Uq50g4p6xw+gLiZA3jfnjy5w=",
       "optional": true
     },
+    "immer": {
+      "version": "9.0.12",
+      "resolved": "https://registry.npmjs.org/immer/-/immer-9.0.12.tgz",
+      "integrity": "sha512-lk7UNmSbAukB5B6dh9fnh5D0bJTOFKxVg2cyJWTYrWRfhLrLMBquONcUs3aFq507hNoIZEDDh8lb8UtOizSMhA=="
+    },
     "import-fresh": {
       "version": "3.2.1",
       "resolved": "https://registry.npmjs.org/import-fresh/-/import-fresh-3.2.1.tgz",
diff --git a/package.json b/package.json
index f903f221..a1db187c 100644
--- a/package.json
+++ b/package.json
@@ -68,6 +68,7 @@
     "classnames": "2.2.5",
     "clipper-lib": "6.2.1",
     "earcut": "2.1.1",
+    "immer": "^9.0.12",
     "less": "^3.11.1",
     "libtess": "1.2.2",
     "lodash": "^4.17.15",
diff --git a/web/app/cad/assembly/assemblyPlugin.ts b/web/app/cad/assembly/assemblyPlugin.ts
index b6fe0bed..fab7819e 100644
--- a/web/app/cad/assembly/assemblyPlugin.ts
+++ b/web/app/cad/assembly/assemblyPlugin.ts
@@ -49,7 +49,7 @@ export function activate(ctx: ApplicationContext) {
   }
 
   function solveAssembly(): void {
-    if (ctx.craftService.isEditingHistory()) {
+    if (ctx.craftService.isEditingHistory) {
       console.log('skipping assembly resolve request in the history mode');
       return;
     }
diff --git a/web/app/cad/craft/craftPlugin.ts b/web/app/cad/craft/craftPlugin.ts
index 4867ccf7..17711ebf 100644
--- a/web/app/cad/craft/craftPlugin.ts
+++ b/web/app/cad/craft/craftPlugin.ts
@@ -1,4 +1,4 @@
-import {addModification, stepOverriding} from './craftHistoryUtils';
+import {addModification, finishHistoryEditing, stepOverriding} from './craftHistoryUtils';
 import {Emitter, state, StateStream, stream} from 'lstream';
 import materializeParams from './schema/materializeParams';
 import CadError from '../../utils/errors';
@@ -103,15 +103,16 @@ export function activate(ctx: CoreContext) {
     }
   }
 
-  function isEditingHistory() {
-    const mods = this.modifications$.value;
-    return mods && mods.pointer !== mods.history.length - 1;
-  }
-
    ctx.craftService  = {
-    modify, modifyInHistoryAndStep, reset, rebuild, runRequest, runPipeline,
+
+     get isEditingHistory() {
+       const mods = this.modifications$.value;
+       return mods && mods.pointer !== mods.history.length - 1;
+     },
+
+     modify, modifyInHistoryAndStep, reset, rebuild, runRequest, runPipeline,
     historyTravel: historyTravel(modifications$),
-    modifications$, models$, update$, isEditingHistory, pipelineFailure$
+    modifications$, models$, update$, pipelineFailure$
   };
 
   // @ts-ignore
@@ -244,9 +245,16 @@ export interface OperationResult {
 
 }
 
-interface CraftHistory {
+export interface CraftHistory {
   history: OperationRequest[];
   pointer: number;
+  hints?: CraftHints;
+}
+
+export interface CraftHints {
+
+  noWizardFocus?: boolean;
+
 }
 
 interface CraftService {
@@ -256,9 +264,9 @@ interface CraftService {
   update$: Emitter<void>;
   pipelineFailure$: StateStream<any>
 
-  modify(request: OperationRequest, onAccepted: () => void, onError: () => Error);
+  modify(request: OperationRequest, onAccepted: () => void, onError: (error) => void);
 
-  modifyInHistoryAndStep(request: OperationRequest, onAccepted: () => void, onError: () => Error);
+  modifyInHistoryAndStep(request: OperationRequest, onAccepted: () => void, onError: (error) => void);
 
   reset(modifications: OperationRequest[]);
 
@@ -270,13 +278,13 @@ interface CraftService {
 
   runPipeline(history: OperationRequest[], beginIndex: number, endIndex: number): Promise<void>;
 
-  isEditingHistory(): boolean;
+  isEditingHistory: boolean;
 }
 
 interface HistoryTravel {
   setPointer(pointer, hints:any);
-  begin(hints: any);
-  end(hints: any);
+  begin(hints?: any);
+  end(hints?: any);
   forward(hints: any);
   backward(hints: any);
 }
diff --git a/web/app/cad/craft/e0/occCommandInterface.ts b/web/app/cad/craft/e0/occCommandInterface.ts
index e5e67c32..9c0f5104 100644
--- a/web/app/cad/craft/e0/occCommandInterface.ts
+++ b/web/app/cad/craft/e0/occCommandInterface.ts
@@ -8,6 +8,9 @@ const pushedModels = new Set();
 export const OCI: OCCCommandInterface = new Proxy({}, {
   get: function (target, prop: string, receiver) {
     return prop in target ? target[prop] : function() {
+      if (typeof prop !== 'string') {
+        return undefined;
+      }
       prop = prop.replace(/^_/, '');
       const args = Array.from(arguments).map(arg => {
         const type = typeof arg;
diff --git a/web/app/cad/craft/operationPlugin.ts b/web/app/cad/craft/operationPlugin.ts
index 23be7cea..cc3e666c 100644
--- a/web/app/cad/craft/operationPlugin.ts
+++ b/web/app/cad/craft/operationPlugin.ts
@@ -94,7 +94,7 @@ export interface Operation<R> extends OperationDescriptor<R>{
     icon: string|IconType;
   };
   schemaIndex: SchemaIndex;
-  form: () => React.ReactNode;
+  form: React.FunctionComponent;
   schema: OperationSchema;
 }
 
@@ -107,7 +107,8 @@ export interface OperationDescriptor<R> {
   run: (request: R, opContext: CoreContext) => OperationResult | Promise<OperationResult>;
   paramsInfo: (params: R) => string,
   previewGeomProvider?: (params: R) => OperationGeometryProvider,
-  form: FormDefinition | (() => React.ReactNode),
+  previewer?: any,
+  form: FormDefinition | React.FunctionComponent,
   schema?: OperationSchema,
   onParamsUpdate?: (params, name, value) => void,
 }
diff --git a/web/app/cad/craft/schema/initializeBySchema.ts b/web/app/cad/craft/schema/initializeBySchema.ts
index ff96323b..d2a27362 100644
--- a/web/app/cad/craft/schema/initializeBySchema.ts
+++ b/web/app/cad/craft/schema/initializeBySchema.ts
@@ -1,8 +1,8 @@
-import {TypeRegistry, Types} from "cad/craft/schema/types";
-import {OperationSchema, SchemaField} from "cad/craft/schema/schema";
-import {ApplicationContext} from "context";
+import {Types} from "cad/craft/schema/types";
+import {isValueNotProvided, OperationSchema, SchemaField} from "cad/craft/schema/schema";
+import {CoreContext} from "context";
 
-export default function initializeBySchema(schema: OperationSchema, context: ApplicationContext) {
+export default function initializeBySchema(schema: OperationSchema, context: CoreContext) {
   let fields = Object.keys(schema);
   let obj = {};
   for (let field of fields) {
@@ -42,3 +42,33 @@ export default function initializeBySchema(schema: OperationSchema, context: App
   }
   return obj;
 }
+
+
+export function fillUpMissingFields(params: any, schema: OperationSchema, context: CoreContext) {
+  let fields = Object.keys(schema);
+  for (let field of fields) {
+    const md = schema[field] as SchemaField;
+
+    if (md.optional) {
+      continue;
+    }
+
+    let val = params[field];
+
+    const isPrimitive =
+         md.type !== Types.array
+      && md.type !== Types.object
+      && md.type !== Types.entity;
+
+    if (isPrimitive && isValueNotProvided(val)) {
+      params[field] = md.defaultValue;
+    } else if (md.type === Types.object) {
+      if (!val) {
+        val = {};
+        params[field] = val;
+      }
+      fillUpMissingFields(val, md.schema, context);
+    }
+  }
+
+}
\ No newline at end of file
diff --git a/web/app/cad/craft/schema/materializeParams.ts b/web/app/cad/craft/schema/materializeParams.ts
index b1a3b758..d0885081 100644
--- a/web/app/cad/craft/schema/materializeParams.ts
+++ b/web/app/cad/craft/schema/materializeParams.ts
@@ -1,6 +1,7 @@
 import {TypeRegistry} from "cad/craft/schema/types";
 import {CoreContext} from "context";
 import {
+  isValueNotProvided,
   OperationParams,
   OperationParamsError,
   OperationParamsErrorReporter,
@@ -33,14 +34,13 @@ function materializeParamsImpl(ctx: CoreContext,
                                result: any,
                                parentReportError: OperationParamsErrorReporter) {
 
-  const notProvided = value => value === undefined || value === null || value === '';
 
   for (let field of Object.keys(schema)) {
     const reportError = parentReportError.dot(field);
     const md = schema[field];
     let value = params[field];
 
-    if (notProvided(value)) {
+    if (isValueNotProvided(value)) {
       if (!md.optional) {
         reportError('required');
       }
@@ -52,7 +52,7 @@ function materializeParamsImpl(ctx: CoreContext,
         value = md.resolve(
           ctx, value, md as any, reportError
         )
-        if (notProvided(value) && !md.optional) {
+        if (isValueNotProvided(value) && !md.optional) {
           reportError('required');
         }
       }
diff --git a/web/app/cad/craft/schema/schema.ts b/web/app/cad/craft/schema/schema.ts
index 693f60cf..3c4e181c 100644
--- a/web/app/cad/craft/schema/schema.ts
+++ b/web/app/cad/craft/schema/schema.ts
@@ -93,4 +93,6 @@ export function unwrapMetadata(fieldMd: SchemaField) {
     );
   }
   return fieldMd;
-}
\ No newline at end of file
+}
+
+export const isValueNotProvided = value => value === undefined || value === null || value === '';
diff --git a/web/app/cad/craft/ui/HistoryTimeline.jsx b/web/app/cad/craft/ui/HistoryTimeline.jsx
index d5956704..401d528b 100644
--- a/web/app/cad/craft/ui/HistoryTimeline.jsx
+++ b/web/app/cad/craft/ui/HistoryTimeline.jsx
@@ -16,7 +16,7 @@ import {aboveElement} from 'ui/positionUtils';
   .map(([modifications, operationRegistry, insertOperationReq]) => ({
     ...modifications,
     operationRegistry,
-    inProgressOperation: insertOperationReq.type,
+    inProgressOperation: !!insertOperationReq,
     getOperation: type => operationRegistry[type]||EMPTY_OBJECT
   })))
 @mapContext(({streams, services}) => ({
diff --git a/web/app/cad/craft/wizard/components/Wizard.jsx b/web/app/cad/craft/wizard/components/Wizard.jsx
deleted file mode 100644
index b4abd940..00000000
--- a/web/app/cad/craft/wizard/components/Wizard.jsx
+++ /dev/null
@@ -1,119 +0,0 @@
-import React from 'react';
-import Stack from 'ui/components/Stack';
-import Button from 'ui/components/controls/Button';
-import ButtonGroup from 'ui/components/controls/ButtonGroup';
-
-import ls from './Wizard.less';
-import CadError from '../../../../utils/errors';
-import {FormContext, FormContextData} from './form/Form';
-import connect from 'ui/connect';
-import {combine} from 'lstream';
-import {GenericWizard} from "ui/components/GenericWizard";
-import * as PropTypes from "prop-types";
-import {useStream} from "ui/effects";
-
-@connect((streams, props) => combine(props.context.workingRequest$, props.context.state$)
-  .map(([workingRequest, state]) => ({
-    ...workingRequest,
-    activeParam: state.activeParam,
-    error: state.error
-  })))
-export default class Wizard extends React.Component {
-
-  state = {
-    hasInternalError: false,
-  };
-
-  updateParam = (name, value) => {
-    this.props.context.updateParam(name, value);
-  };
-
-  componentDidCatch() {
-    this.setState({hasInternalError: true});
-  }
-
-  render() {
-    if (this.state.hasInternalError) {
-      return <span>operation error</span>;
-    }
-
-    let {left, type, params, state, context} = this.props;
-    let operation = context.operation;
-
-    let title = (operation.label || type).toUpperCase();
-
-    let Form = operation.form;
-
-    const error = this.props.error;
-    return <GenericWizard
-                   left={left}
-                   title={title}
-                   onClose={this.cancel}
-                   onKeyDown={this.onKeyDown}
-                   setFocus={this.focusFirstInput}
-                   className='Wizard'
-                   data-operation-id={operation.id}
-                   topicId={operation.id}
-                   onCancel={this.cancel}
-                   onOK={this.onOK}
-                   infoText={<>
-                     {error && <ErrorPrinter error={error}/>}
-                     <PipelineError />
-                   </>}
-    >
-      <FormContext.Provider value={new FormContextData(this.props.context, [])}>
-        <Form/>
-      </FormContext.Provider>
-
-    </GenericWizard>;
-  }
-
-  onKeyDown = e => {
-    switch (e.keyCode) {
-      case 27 :
-        this.cancel();
-        break;
-      case 13 :
-        this.onOK();
-        break;
-    }
-  };
-
-  focusFirstInput = el => {
-    if (this.props.noFocus) {
-      return;
-    }
-    let toFocus = el.querySelector('input, select');
-    if (!toFocus) {
-      toFocus = el;
-    }
-    toFocus.focus();
-  };
-
-  cancel = () => {
-    this.props.onCancel();
-  };
-
-  onOK = () => {
-    this.props.onOK();
-  };
-}
-function PipelineError() {
-  const pipelineFailure = useStream(ctx => ctx.craftService.pipelineFailure$);
-  if (!pipelineFailure) {
-    return null;
-  }
-  return <ErrorPrinter error={pipelineFailure}/>
-}
-
-function ErrorPrinter({error}) {
-  return <div className={ls.errorMessage}>
-    {CadError.ALGORITHM_ERROR_KINDS.includes(error.kind) && <span>
-                        performing operation with current parameters leads to an invalid object
-                        (self-intersecting / zero-thickness / complete degeneration or unsupported cases)
-                      </span>}
-    {error.code && <div className={ls.errorCode}>{error.code}</div>}
-    {error.userMessage && <div className={ls.userErrorMessage}>{error.userMessage}</div>}
-    {!error.userMessage && <div>internal error processing operation, check the log</div>}
-  </div>
-}
diff --git a/web/app/cad/craft/wizard/components/Wizard.tsx b/web/app/cad/craft/wizard/components/Wizard.tsx
new file mode 100644
index 00000000..e48f0f29
--- /dev/null
+++ b/web/app/cad/craft/wizard/components/Wizard.tsx
@@ -0,0 +1,122 @@
+import React, {useContext} from 'react';
+
+import ls from './Wizard.less';
+import CadError from '../../../../utils/errors';
+import {FormParamsContext, FormPathContext, FormStateContext} from './form/Form';
+import {GenericWizard} from "ui/components/GenericWizard";
+import {useStream} from "ui/effects";
+import {AppContext} from "cad/dom/components/AppContext";
+
+interface WizardProps {
+  noFocus: boolean;
+
+  left?: number;
+
+  onCancel(): void;
+
+  onOK(): void;
+}
+
+export default function Wizard(props: WizardProps) {
+
+  const ctx = useContext(AppContext);
+  const state = useStream(ctx => ctx.wizardService.state$);
+  const workingRequest = useStream(ctx =>  ctx.wizardService.workingRequest$);
+
+  if (!workingRequest) {
+    return;
+  }
+
+  const operation = ctx.operationService.get(workingRequest.type);
+
+  if (!operation) {
+    return;
+  }
+
+  const error = state.error;
+
+  const onKeyDown = e => {
+    switch (e.keyCode) {
+      case 27 :
+        cancel();
+        break;
+      case 13 :
+        onOK();
+        break;
+    }
+  };
+
+  const focusFirstInput = el => {
+    if (props.noFocus) {
+      return;
+    }
+    let toFocus = el.querySelector('input, select');
+    if (!toFocus) {
+      toFocus = el;
+    }
+    toFocus.focus();
+  };
+
+  const cancel = () => {
+    props.onCancel();
+  };
+
+  const onOK = () => {
+    props.onOK();
+  };
+
+  let {left} = props;
+  let wizardService = ctx.wizardService;
+
+  let title = (operation.label || operation.id).toUpperCase();
+
+  let Form = operation.form;
+
+  return <GenericWizard
+    left={left}
+    title={title}
+    onClose={cancel}
+    onKeyDown={onKeyDown}
+    setFocus={focusFirstInput}
+    className='Wizard'
+    data-operation-id={operation.id}
+    topicId={operation.id}
+    onCancel={cancel}
+    onOK={onOK}
+    infoText={<>
+      {error && <ErrorPrinter error={error}/>}
+      <PipelineError />
+    </>}
+  >
+
+    <FormParamsContext.Provider value={workingRequest.params}>
+      <FormPathContext.Provider value={[]}>
+        <FormStateContext.Provider value={state}>
+          <Form/>
+        </FormStateContext.Provider>
+      </FormPathContext.Provider>
+    </FormParamsContext.Provider>
+
+  </GenericWizard>;
+}
+
+
+function PipelineError() {
+  const pipelineFailure = useStream(ctx => ctx.craftService.pipelineFailure$);
+  if (!pipelineFailure) {
+    return null;
+  }
+  return <ErrorPrinter error={pipelineFailure}/>
+}
+
+function ErrorPrinter({error}) {
+  return <div className={ls.errorMessage}>
+    {CadError.ALGORITHM_ERROR_KINDS.includes(error.kind) && <span>
+                        performing operation with current parameters leads to an invalid object
+                        (self-intersecting / zero-thickness / complete degeneration or unsupported cases)
+                      </span>}
+    {error.code && <div className={ls.errorCode}>{error.code}</div>}
+    {error.userMessage && <div className={ls.userErrorMessage}>{error.userMessage}</div>}
+    {!error.userMessage && <div>internal error processing operation, check the log</div>}
+  </div>
+}
diff --git a/web/app/cad/craft/wizard/components/WizardManager.jsx b/web/app/cad/craft/wizard/components/WizardManager.jsx
deleted file mode 100644
index 97fdd810..00000000
--- a/web/app/cad/craft/wizard/components/WizardManager.jsx
+++ /dev/null
@@ -1,27 +0,0 @@
-import React from 'react';
-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({wizardContext, type, cancel, cancelHistoryEdit, applyWorkingRequest}) {
-  if (!wizardContext) {
-    return null;
-  }
-  return <Wizard key={wizardContext.ID}
-                 context={wizardContext}
-                 noFocus={wizardContext.noWizardFocus}
-                 onCancel={wizardContext.changingHistory ? cancelHistoryEdit : cancel}
-                 onOK={applyWorkingRequest} />
-}
-
-export default decoratorChain(
-  connect(streams => streams.wizard.wizardContext.map(wizardContext => ({wizardContext}))),
-  mapContext(ctx => ({
-    cancel: ctx.services.wizard.cancel,
-    cancelHistoryEdit: () => ctx.streams.craft.modifications.update(modifications => finishHistoryEditing(modifications)),
-    applyWorkingRequest: ctx.services.wizard.applyWorkingRequest 
-  }))
-)
-(WizardManager);
diff --git a/web/app/cad/craft/wizard/components/WizardManager.tsx b/web/app/cad/craft/wizard/components/WizardManager.tsx
new file mode 100644
index 00000000..ac60cfa8
--- /dev/null
+++ b/web/app/cad/craft/wizard/components/WizardManager.tsx
@@ -0,0 +1,22 @@
+import React, {useContext} from 'react';
+import Wizard from './Wizard';
+import {useStream} from "ui/effects";
+import {AppContext} from "cad/dom/components/AppContext";
+import {ErrorBoundary} from "ui/errorBoundary";
+
+export default function WizardManager() {
+
+  const ctx = useContext(AppContext);
+  const workingRequest = useStream(ctx => ctx.wizardService.workingRequest$);
+
+  if (!workingRequest) {
+    return null;
+  }
+
+  return <ErrorBoundary key={workingRequest.requestKey}
+                        message={<span>operation error</span>}>
+    <Wizard noFocus={workingRequest.hints?.noWizardFocus}
+            onCancel={ctx.craftService.isEditingHistory ? ctx.craftService.historyTravel.end : ctx.wizardService.cancel}
+            onOK={ctx.wizardService.applyWorkingRequest} />
+  </ErrorBoundary>
+}
diff --git a/web/app/cad/craft/wizard/components/form/Form.tsx b/web/app/cad/craft/wizard/components/form/Form.tsx
index adccd7a2..81bcde3a 100644
--- a/web/app/cad/craft/wizard/components/form/Form.tsx
+++ b/web/app/cad/craft/wizard/components/form/Form.tsx
@@ -1,43 +1,17 @@
-import React from 'react';
+import React, {useContext} from 'react';
 import Label from 'ui/components/controls/Label';
 import Field from 'ui/components/controls/Field';
 import Stack from 'ui/components/Stack';
 import {camelCaseSplitToStr} from 'gems/camelCaseSplit';
-import {FlattenPath, ParamsPath, ParamsPathSegment, WizardContext} from "cad/craft/wizard/wizardTypes";
-import {flattenPath, OperationParamValue} from "cad/craft/schema/schema";
+import {ParamsPath, ParamsPathSegment, WizardState} from "cad/craft/wizard/wizardTypes";
+import {OperationParams, OperationParamValue} from "cad/craft/schema/schema";
+import {AppContext} from "cad/dom/components/AppContext";
+import _ from "lodash";
 
-export const FormContext: React.Context<FormContextData> = React.createContext(null);
+export const FormStateContext: React.Context<WizardState> = React.createContext(null);
+export const FormParamsContext: React.Context<OperationParams> = React.createContext(null);
+export const FormPathContext: React.Context<ParamsPath> = React.createContext([]);
 
-export class FormContextData  {
-
-  wizardContext: WizardContext;
-  prefix: ParamsPath;
-
-  constructor(wizardContext: WizardContext, prefix: ParamsPath) {
-    this.wizardContext = wizardContext;
-    this.prefix = prefix;
-  }
-
-  updateParam(segment: ParamsPathSegment, value: OperationParamValue): void {
-    this.wizardContext.updateParam([...this.prefix, segment], value);
-  }
-
-  readParam(segment: ParamsPathSegment): OperationParamValue {
-    return this.wizardContext.readParam([...this.prefix, segment]);
-  }
-
-  dot(segment: ParamsPathSegment): FormContextData {
-    return new FormContextData(this.wizardContext, [...this.prefix, segment]);
-  }
-
-  setActiveParam = (path: FlattenPath) => {
-    this.wizardContext.updateState(state => state.activeParam = path);
-  }
-
-  get activeParam(): FlattenPath {
-    return this.wizardContext.state$.value.activeParam;
-  }
-}
 
 export function Group({children}) {
   return <Stack>
@@ -61,36 +35,42 @@ interface FormFieldProps {
   children?: any
 }
 
-export function attachToForm(Control) {
+export function attachToForm(Control): any {
+
   return function FormField({name, ...props}: FormFieldProps) {
-    return <FormContext.Consumer>
-      {
-        (ctx: FormContextData) => {
-          const fullPath = flattenPath([...ctx.prefix, name]);
-          const onChange = val => ctx.updateParam(name, val);
-          const setActive = val => ctx.setActiveParam(val ? fullPath : undefined);
-          return <React.Fragment>
-            <Control value={ctx.readParam(name)}
-                     onChange={onChange} 
-                     name={name} {...props}
-                     setActive={setActive}
-                     active={ctx.activeParam === fullPath} />
-          </React.Fragment>;
-        }
-      }
-    </FormContext.Consumer>;
+
+    const ctx = useContext(AppContext);
+    const formPath = useContext(FormPathContext);
+    const formState = useContext(FormStateContext);
+    const params = useContext(FormParamsContext);
+
+    const fullPath = [...formPath, name];
+    const fullPathFlatten = fullPath.join('.');
+    const onChange = value => ctx.wizardService.updateParam(fullPath, value);
+    const setActive = (isActive) => ctx.wizardService.updateState(state => {
+      state.activeParam = isActive ? fullPathFlatten : null;
+    });
+
+    const value = _.get(params, fullPath);
+
+    return <React.Fragment>
+      <Control value={value}
+               onChange={onChange}
+               name={name} {...props}
+               setActive={setActive}
+               active={formState.activeParam === fullPathFlatten} />
+    </React.Fragment>;
   };
 }
 
 export function SubForm(props: {name: ParamsPathSegment, children: any}) {
 
-  return <FormContext.Consumer>
-    {
-      (ctx: FormContextData) => {
-        return <FormContext.Provider value={ctx.dot(props.name)}>
-          {props.children}
-        </FormContext.Provider>
-      }
-    }
-  </FormContext.Consumer>
+  const formState = useContext(FormStateContext);
+  const formPath = useContext(FormPathContext);
+
+  return <FormParamsContext.Provider value={formState[props.name]}>
+    <FormPathContext.Provider value={[...formPath, props.name]}>
+      {props.children}
+    </FormPathContext.Provider>
+  </FormParamsContext.Provider>;
 }
\ No newline at end of file
diff --git a/web/app/cad/craft/wizard/wizardPlugin.ts b/web/app/cad/craft/wizard/wizardPlugin.ts
index 05c7f491..ac47ba87 100644
--- a/web/app/cad/craft/wizard/wizardPlugin.ts
+++ b/web/app/cad/craft/wizard/wizardPlugin.ts
@@ -1,163 +1,181 @@
-import {state} from 'lstream';
-import initializeBySchema from '../schema/initializeBySchema';
-import {clone, EMPTY_OBJECT} from 'gems/objects';
+import {combine, state, StateStream} from 'lstream';
+import initializeBySchema, {fillUpMissingFields} from '../schema/initializeBySchema';
+import {clone} from 'gems/objects';
 import materializeParams from '../schema/materializeParams';
 import {createFunctionList} from 'gems/func';
-import {OperationRequest} from "cad/craft/craftPlugin";
-import {ParamsPath, WizardContext, WizardState} from "cad/craft/wizard/wizardTypes";
+import {CraftHints, CraftHistory, OperationRequest} from "cad/craft/craftPlugin";
+import {NewOperationCall, ParamsPath, WizardService, WizardState} from "cad/craft/wizard/wizardTypes";
 import _ from "lodash";
 import {OperationParamValue} from "cad/craft/schema/schema";
+import {ApplicationContext} from "context";
+import {Operation} from "cad/craft/operationPlugin";
+import produce from "immer"
 
-export function activate(ctx) {
+type WorkingRequest = OperationRequest & {
+  hints?: CraftHints,
+  requestKey: number
+}
+
+export function activate(ctx: ApplicationContext) {
 
   let {streams, services} = ctx;
 
-  streams.wizard = {};
-  
-  streams.wizard.insertOperation = state(EMPTY_OBJECT);
+  const insertOperation$ = state<NewOperationCall>(null);
 
-  streams.wizard.effectiveOperation = state(EMPTY_OBJECT);
+  let REQUEST_COUNTER = 1;
 
-  streams.wizard.insertOperation.attach(insertOperationReq => {
-    if (insertOperationReq.type) {
-      let type = insertOperationReq.type;
-      let operation = ctx.services.operation.get(type);
-      streams.wizard.effectiveOperation.value = {
-        type: operation.id,
-        initialOverrides: insertOperationReq.initialOverrides,
-        changingHistory: false
-      };
-    }
-  });
-  
-  function gotoEditHistoryModeIfNeeded({pointer, history, hints}) {
-    if (pointer !== history.length - 1) {
-      let {type, params} = history[pointer + 1];
-      streams.wizard.effectiveOperation.value =  {
-        type,
-        params,
-        noWizardFocus: hints && hints.noWizardFocus,
-        changingHistory: true
-      };
-    } else {
-      streams.wizard.effectiveOperation.value = EMPTY_OBJECT;
-    }
+  const workingRequest$: StateStream<WorkingRequest> = combine<[NewOperationCall, CraftHistory]>(
+    insertOperation$,
+    ctx.craftService.modifications$
+  ).map<NewOperationCall|OperationRequest>(([insertOperationReq, mods]) => {
 
-  }
-  
-  streams.craft.modifications.attach(mod => {
-    if (streams.wizard.insertOperation.value.type) {
-      return;
-    }
-    gotoEditHistoryModeIfNeeded(mod);
-  });
+    let operation;
+    let params;
 
-  streams.wizard.wizardContext = streams.wizard.effectiveOperation.map((opRequest: OperationRequest) => {
-    let wizCtx: WizardContext = null;
-    if (opRequest.type) {
-      
-      let operation = ctx.services.operation.get(opRequest.type);
-
-      let params;
-      let {changingHistory, noWizardFocus} = opRequest;
-      if (changingHistory) {
-        params = clone(opRequest.params)
-      } else {
-        params = initializeBySchema(operation.schema, ctx);
-        if (opRequest.initialOverrides) {
-          applyOverrides(params, opRequest.initialOverrides);
-        }
+    if (insertOperationReq !== null) {
+      operation = ctx.operationService.get(insertOperationReq.type);
+      params = initializeBySchema(operation.schema, ctx);
+      if (insertOperationReq.initialOverrides) {
+        applyOverrides(params, insertOperationReq.initialOverrides);
       }
 
-      let workingRequest$ = state({
-        type: opRequest.type,
-        params
-      });
-      
-      let materializedWorkingRequest$ = workingRequest$.map(req => {
-        let params = {};
-        let errors = [];
-        materializeParams(ctx, req.params, operation.schema, params, errors);
-        if (errors.length !== 0) {
-          return INVALID_REQUEST;
-        }
+      return {
+        type: operation.id,
+        params,
+        requestKey: REQUEST_COUNTER++
+      }
+    } else {
+      const {pointer, history, hints} = mods
+      if (pointer !== history.length - 1) {
+        let {type, params} = history[pointer + 1];
         return {
-          type: req.type,
-          params
+          type,
+          params: clone(params),
+          hints,
+          requestKey: REQUEST_COUNTER++
         };
-      }).remember(INVALID_REQUEST).filter(r => r !== INVALID_REQUEST).throttle(500);
-      const state$ = state<WizardState>({
-        activeParam: null
-      });
-      const updateParams = mutator => workingRequest$.mutate(data => mutator(data.params));
-      const updateState = mutator => state$.mutate(state => mutator(state));
-      const updateParam = (path: ParamsPath, value: OperationParamValue) => {
-        updateParams(params => {
-          // if (operation.onParamsUpdate) {
-          //   operation.onParamsUpdate(params, name, value, params[name]);
-          // }
-          if (!Array.isArray(path)) {
-            path = [path]
-          }
-          _.set(params, path, value);
-        });
-      };
-
-      const readParam = (path: ParamsPath) => {
-        return _.get(params, path);
-      };
-
-      const disposerList = createFunctionList();
-      wizCtx = {
-        workingRequest$, materializedWorkingRequest$, state$,
-        updateParams, updateParam, readParam, updateState,
-        operation, changingHistory, noWizardFocus,
-        addDisposer: disposerList.add,
-        dispose: disposerList.call,
-        ID: ++REQUEST_COUNTER,
-      };
+      } else {
+        return null;
+      }
     }
-    return wizCtx;
+
   }).remember(null);
 
-  streams.wizard.wizardContext.pairwise().attach(([oldContext, newContext]) => {
-    if (oldContext) {
-      oldContext.dispose();
-    } 
-  });
-  
-  services.wizard = {
+  const materializedWorkingRequest$ = workingRequest$.map(req => {
+    if (req == null) {
+      return null;
+    }
+    let params = {};
+    let errors = [];
+    let operation = ctx.services.operation.get(req.type);
 
-    open: (type, initialOverrides) => {
-      streams.wizard.insertOperation.value = {
+    materializeParams(ctx, req.params, operation.schema, params, errors);
+    if (errors.length !== 0) {
+      return null;
+    }
+    return {
+      type: req.type,
+      params
+    };
+  }).remember(null).filter(r => r !== null).throttle(500);
+
+  const state$ = state<WizardState>({});
+  let disposerList = createFunctionList();
+
+  // reset effect
+  workingRequest$.pairwise().attach(([old, curr]) => {
+    if (old !== null && old.requestKey !== curr?.requestKey) {
+      console.log("=========> DISPOSE")
+      disposerList.call();
+      disposerList = createFunctionList();
+      state$.next({});
+    }
+  })
+
+  const updateParams = mutator => workingRequest$.update((req: WorkingRequest) => produce(req, draft => mutator(draft.params)));
+  const updateState = mutator => state$.update((state: WizardState) => produce(state, mutator));
+  const updateParam = (path: ParamsPath, value: OperationParamValue) => {
+    updateParams(params => {
+      // if (operation.onParamsUpdate) {
+      //   operation.onParamsUpdate(params, name, value, params[name]);
+      // }
+      if (!Array.isArray(path)) {
+        path = [path]
+      }
+      _.set(params, path, value);
+    });
+  };
+
+  const readParam = (path: ParamsPath) => {
+    return _.get(workingRequest$.value.params, path);
+  };
+
+  const getWorkingRequest = () => workingRequest$.value;
+
+  //legacy
+  streams.wizard = {
+    insertOperation: insertOperation$,
+  };
+
+  const cancel = () => {
+    insertOperation$.next(null);
+  };
+
+  const wizardService: WizardService = {
+
+    open: (type: string, initialOverrides: NewOperationCall) => {
+      streams.wizard.insertOperation.next({
         type,
         initialOverrides
-      };
+      });
     },
 
-    cancel: () => {
-      streams.wizard.insertOperation.value = EMPTY_OBJECT;
-      gotoEditHistoryModeIfNeeded(streams.craft.modifications.value);
-    },
+    cancel,
     
     applyWorkingRequest: () => {
-      let {type, params} = streams.wizard.wizardContext.value.workingRequest$.value;
+      let {type, params} = getWorkingRequest();
       let request = clone({type, params});
-      const setError = error => streams.wizard.wizardContext.mutate(ctx => ctx.state$.mutate(state => state.error = error));
-      if (streams.wizard.insertOperation.value.type) {
-        ctx.services.craft.modify(request, () => streams.wizard.insertOperation.value = EMPTY_OBJECT, setError );
+      const setError = error => state$.mutate(state => state.error = error);
+      if (insertOperation$.value) {
+        ctx.craftService.modify(request, cancel, setError);
       } else {
-        ctx.services.craft.modifyInHistoryAndStep(request, () => streams.wizard.effectiveOperation.value = EMPTY_OBJECT, setError);
+        ctx.craftService.modifyInHistoryAndStep(request, () => {}, setError);
       }
     },
     
-    isInProgress: () => streams.wizard.wizardContext.value !== null
+    isInProgress: () => getWorkingRequest() !== null,
+
+    get workingRequest() {
+      return getWorkingRequest();
+    },
+
+    get materializedWorkingRequest() {
+      return materializedWorkingRequest$.value;
+    },
+
+    get operation(): Operation<any> {
+      const req = getWorkingRequest();
+      if (!req) {
+        return null;
+      }
+      return ctx.operationService.get(req.type);
+    },
+
+    workingRequest$, materializedWorkingRequest$, state$,
+    updateParams, updateParam, readParam, updateState,
+    addDisposer: disposerList.add
   };
+
+  ctx.wizardService = services.wizard = wizardService;
 }
 
+declare module 'context' {
+  interface ApplicationContext {
+    wizardService: WizardService
+  }
+}
+
+
 function applyOverrides(params, initialOverrides) {
   Object.assign(params, initialOverrides);
 }
-
-const INVALID_REQUEST = {};
-let REQUEST_COUNTER = 0;
\ No newline at end of file
diff --git a/web/app/cad/craft/wizard/wizardSelectionPlugin.ts b/web/app/cad/craft/wizard/wizardSelectionPlugin.ts
index 5879aa1a..58b510f8 100644
--- a/web/app/cad/craft/wizard/wizardSelectionPlugin.ts
+++ b/web/app/cad/craft/wizard/wizardSelectionPlugin.ts
@@ -1,37 +1,36 @@
-import {FACE, SHELL} from '../../model/entities';
+import {FACE, SHELL} from 'cad/model/entities';
 import {memoize} from "lodash/function";
-import {Types} from "cad/craft/schema/types";
 import {OperationRequest} from "cad/craft/craftPlugin";
-import {FlattenPath, ParamsPath, WizardContext} from "cad/craft/wizard/wizardTypes";
-import {OperationParamValue, SchemaField} from "cad/craft/schema/schema";
-import {EntityReference, SchemaIndexField} from "cad/craft/operationPlugin";
+import {FlattenPath, ParamsPath, WizardService} from "cad/craft/wizard/wizardTypes";
+import {OperationParamValue} from "cad/craft/schema/schema";
+import {EntityReference} from "cad/craft/operationPlugin";
+import {ApplicationContext} from "context";
 
-export function activate(ctx) {
-  ctx.streams.wizard.wizardContext.attach((wizCtx: WizardContext) => {
+export function activate(ctx: ApplicationContext) {
+  const wizardService = ctx.wizardService;
+  wizardService.workingRequest$.attach((opRequest: OperationRequest) => {
     ctx.services.marker.clear();
-    if (wizCtx) {
-      const wizardPickHandler = createPickHandlerFromSchema(wizCtx);
+    if (opRequest) {
+      const wizardPickHandler = createPickHandlerFromSchema(wizardService);
       ctx.services.pickControl.setPickHandler(wizardPickHandler);
-      wizCtx.workingRequest$.attach(({type, params}: OperationRequest) => {
-        const marker = ctx.services.marker;
-        marker.startSession();
-        let {schemaIndex} = wizCtx.operation;
-        schemaIndex.entities.forEach(entityRef => {
-          //TODO: move to uiDefinition
-          let color = entityRef.metadata.markColor;
+      const marker = ctx.services.marker;
+      marker.startSession();
+      let {schemaIndex} = wizardService.operation;
+      schemaIndex.entities.forEach(entityRef => {
+        //TODO: move to uiDefinition
+        let color = entityRef.metadata.markColor;
 
-          let val = wizCtx.readParam(entityRef.field.path);
+        let val = wizardService.readParam(entityRef.field.path);
 
-          if (Array.isArray(val)) {
-            val.forEach(id => marker.mark(id, color));
-          } else {
-            if (val) {
-              marker.mark(val, color);
-            }
+        if (Array.isArray(val)) {
+          val.forEach(id => marker.mark(id, color));
+        } else {
+          if (val) {
+            marker.mark(val, color);
           }
-        });
-        marker.commit();
+        }
       });
+      marker.commit();
 
     } else {
       ctx.services.pickControl.setPickHandler(null);
@@ -52,20 +51,20 @@ const arrayValue = (id, arr) =>  {
 
 const getEntityParams = memoize(schema => Object.keys(schema).filter(key => schema[key].type === 'entity'));
 
-function createPickHandlerFromSchema(wizCtx: WizardContext) {
+function createPickHandlerFromSchema(wizardService: WizardService) {
 
   function update(param: ParamsPath, value: OperationParamValue, paramToMakeActive: FlattenPath) {
-    wizCtx.updateParam(param, value);
-    wizCtx.updateState(state => {
+    wizardService.updateParam(param, value);
+    wizardService.updateState(state => {
       state.activeParam = paramToMakeActive;
     });
   }
   return model => {
     const modelType = model.TYPE;
 
-    let {schemaIndex} = wizCtx.operation;
+    let {schemaIndex} = wizardService.operation;
     let activeEntityRef = () => {
-      const state = wizCtx.state$.value;
+      const state = wizardService.state$.value;
       return schemaIndex.entitiesByFlattenedPaths[state.activeParam];
     }
 
@@ -83,7 +82,7 @@ function createPickHandlerFromSchema(wizCtx: WizardContext) {
       const param = entityRef.field;
       const valueGetter = entityRef.isArray ? arrayValue : singleValue;
       let paramToMakeActive = getNextActiveParam(entityRef);
-      const currentValue = wizCtx.readParam(param.path);
+      const currentValue = wizardService.readParam(param.path);
       update(param.path, valueGetter(id, currentValue), paramToMakeActive.field.flattenedPath);
     }
 
@@ -111,7 +110,7 @@ function createPickHandlerFromSchema(wizCtx: WizardContext) {
 
     function deselectIfNeeded(id) {
       for (let entityRef of schemaIndex.entities) {
-        let val = wizCtx.readParam(entityRef.field.path);
+        let val = wizardService.readParam(entityRef.field.path);
         if (val === id) {
           update(entityRef.field.path, undefined, entityRef.field.flattenedPath);
           return true;
diff --git a/web/app/cad/craft/wizard/wizardTypes.ts b/web/app/cad/craft/wizard/wizardTypes.ts
index 32db8be1..6a052ece 100644
--- a/web/app/cad/craft/wizard/wizardTypes.ts
+++ b/web/app/cad/craft/wizard/wizardTypes.ts
@@ -1,5 +1,5 @@
 import {StateStream} from "lstream";
-import {OperationRequest} from "cad/craft/craftPlugin";
+import {CraftHints, OperationRequest} from "cad/craft/craftPlugin";
 import {MaterializedOperationParams, OperationParamValue, OperationParams} from "cad/craft/schema/schema";
 import {Operation} from "cad/craft/operationPlugin";
 
@@ -10,17 +10,30 @@ export type ParamsPath = ParamsPathSegment[];
 export type FlattenPath = string;
 
 export type WizardState = {
-  activeParam: FlattenPath
+  activeParam?: FlattenPath
+  error?: any
 };
 
-export interface WizardContext {
+export interface WizardService {
 
-  workingRequest$: StateStream<OperationRequest>;
+  workingRequest$: StateStream<OperationRequest&{hints?: CraftHints}>;
 
   materializedWorkingRequest$: StateStream<MaterializedOperationParams>;
 
   state$: StateStream<WizardState>;
 
+  open(type: string, initialOverrides: NewOperationCall);
+
+  cancel();
+
+  applyWorkingRequest();
+
+  isInProgress(): boolean;
+
+  workingRequest: OperationRequest;
+
+  materializedWorkingRequest: any;
+
   updateParams: (mutator: (params: OperationParams) => void) => void;
 
   updateParam: (path: ParamsPath, value: OperationParamValue) => void;
@@ -31,13 +44,11 @@ export interface WizardContext {
 
   operation: Operation<any>;
 
-  changingHistory: boolean;
-
-  noWizardFocus: boolean;
-
   addDisposer: (disposer: () => any|void) => void;
 
-  dispose: () => void;
+}
 
-  ID: number;
+export interface NewOperationCall {
+  type: string;
+  initialOverrides: OperationParams;
 }
\ No newline at end of file
diff --git a/web/app/cad/mdf/ui/ChoiceWidget.tsx b/web/app/cad/mdf/ui/ChoiceWidget.tsx
index 62af6f6d..d6bda270 100644
--- a/web/app/cad/mdf/ui/ChoiceWidget.tsx
+++ b/web/app/cad/mdf/ui/ChoiceWidget.tsx
@@ -1,10 +1,8 @@
-import {ComboBoxField, NumberField} from "cad/craft/wizard/components/form/Fields";
+import {ComboBoxField} from "cad/craft/wizard/components/form/Fields";
 import React from "react";
-import {flattenPath, OperationSchema} from "cad/craft/schema/schema";
 import {FieldBasicProps, fieldToSchemaGeneric} from "cad/mdf/ui/field";
 import {Types} from "cad/craft/schema/types";
 import {ComboBoxOption} from "ui/components/controls/ComboBoxControl";
-import {FormContext, FormContextData} from "cad/craft/wizard/components/form/Form";
 
 export interface ChoiceWidgetProps extends FieldBasicProps {
 
@@ -19,21 +17,10 @@ export interface ChoiceWidgetProps extends FieldBasicProps {
 export function ChoiceWidget(props: ChoiceWidgetProps) {
   if (!props.style || props.style === 'dropdown') {
 
-    return <FormContext.Consumer>
-      {
-        (ctx: FormContextData) => {
-          const value = ctx.readParam(props.name);
-          let nonExistent = null;
-          if (!props.values.includes(value as any)) {
-            nonExistent = <ComboBoxOption value={value}>{value ?  value+'' : '<empty>'}</ComboBoxOption>
-          }
-          return <ComboBoxField name={props.name} defaultValue={props.defaultValue} label={props.label} >
-            {nonExistent}
-            {props.values.map(value => <ComboBoxOption value={value} key={value}>{value}</ComboBoxOption>)}
-          </ComboBoxField>;
-        }
-      }
-    </FormContext.Consumer>
+    return <ComboBoxField name={props.name} defaultValue={props.defaultValue} label={props.label} includeNonExistent>
+      {props.values.map(value => <ComboBoxOption value={value} key={value}>{value}</ComboBoxOption>)}
+    </ComboBoxField>;
+
   } else {
     throw 'implement me';
   }
diff --git a/web/app/cad/preview/previewPlugin.js b/web/app/cad/preview/previewPlugin.js
deleted file mode 100644
index 1c39b57b..00000000
--- a/web/app/cad/preview/previewPlugin.js
+++ /dev/null
@@ -1,40 +0,0 @@
-import {createPreviewer} from './scenePreviewer';
-
-export function activate(ctx) {
-  let {streams, services} = ctx;
-  
-  streams.wizard.wizardContext.attach(wizCtx => {
-    if (!wizCtx) {
-      return;
-    }
-    let {operation, materializedWorkingRequest$} = wizCtx; 
-    if (operation.previewGeomProvider || operation.previewer) {
-      let previewer = null;
-      materializedWorkingRequest$.attach(({type, params}) => {
-        if (previewer === null) {
-          try {
-            if (operation.previewGeomProvider) {
-              previewer = createPreviewer(operation.previewGeomProvider, services, params);
-            } else if (operation.previewer) {
-              previewer = operation.previewer(ctx, params, wizCtx.updateParams);
-            }
-          } catch (e) {
-            console.error(e);
-            return;
-          }
-          wizCtx.addDisposer(() => {
-            previewer.dispose();
-            ctx.services.viewer.requestRender();
-          });
-        } else {
-          try {
-            previewer.update(params);
-          } catch (e) {
-            console.error(e);
-          }
-        }
-        ctx.services.viewer.requestRender();
-      });
-    }
-  });
-}
\ No newline at end of file
diff --git a/web/app/cad/preview/previewPlugin.ts b/web/app/cad/preview/previewPlugin.ts
new file mode 100644
index 00000000..ebc671ad
--- /dev/null
+++ b/web/app/cad/preview/previewPlugin.ts
@@ -0,0 +1,42 @@
+import {createPreviewer} from './scenePreviewer';
+import {ApplicationContext} from "context";
+
+export function activate(ctx: ApplicationContext) {
+  let previewer = null;
+  ctx.wizardService.materializedWorkingRequest$.attach(materializedWorkingRequest => {
+    if (!materializedWorkingRequest) {
+      previewer = null;
+      return;
+    }
+    const {type, params} = materializedWorkingRequest;
+    const operation = ctx.wizardService.operation;
+    if (operation.previewGeomProvider || operation.previewer) {
+      if (previewer === null) {
+        let newPreviewer;
+        try {
+          if (operation.previewGeomProvider) {
+            newPreviewer = createPreviewer(operation.previewGeomProvider, ctx.services, params);
+          } else if (operation.previewer) {
+            newPreviewer = operation.previewer(ctx, params, ctx.wizardService.updateParams);
+          }
+          previewer = newPreviewer;
+        } catch (e) {
+          console.error(e);
+          return;
+        }
+        ctx.wizardService.addDisposer(() => {
+          newPreviewer.dispose();
+          previewer = null;
+          ctx.services.viewer.requestRender();
+        });
+      } else {
+        try {
+          previewer.update(params);
+        } catch (e) {
+          console.error(e);
+        }
+      }
+      ctx.services.viewer.requestRender();
+    }
+  });
+}
\ No newline at end of file
diff --git a/web/app/cad/projectPlugin.ts b/web/app/cad/projectPlugin.ts
index e6a7dd3f..e9ffdc6c 100644
--- a/web/app/cad/projectPlugin.ts
+++ b/web/app/cad/projectPlugin.ts
@@ -6,6 +6,7 @@ import {SketchFormat_V3} from "../sketcher/io";
 import {OperationRequest} from "./craft/craftPlugin";
 import {ProjectModel} from "./projectManager/projectManagerPlugin";
 import {DebugMode$} from "debugger/Debugger";
+import {fillUpMissingFields} from "cad/craft/schema/initializeBySchema";
 
 export const STORAGE_GLOBAL_PREFIX = 'TCAD';
 export const PROJECTS_PREFIX = `${STORAGE_GLOBAL_PREFIX}.projects.`;
@@ -54,6 +55,7 @@ export function initProjectService(ctx: CoreContext, id: string, hints: any) {
       let dataStr = ctx.storageService.get(ctx.projectService.projectStorageKey());
       if (dataStr) {
         let data = JSON.parse(dataStr);
+        upgradeIfNeeded(data);
         loadData(data);
       }
     } catch (e) {
@@ -61,6 +63,16 @@ export function initProjectService(ctx: CoreContext, id: string, hints: any) {
     }
   }
 
+  function upgradeIfNeeded(data: ProjectModel) {
+    if (data.history) {
+      data.history.forEach(req => {
+        const operation = ctx.operationService.get(req.type);
+        if (operation) {
+          fillUpMissingFields(req.params, operation.schema, ctx);
+        }
+      });
+    }
+  }
 
   function loadData(data: ProjectModel) {
     if (data.expressions) {