diff --git a/README.md b/README.md
index 6e75d5a..464b991 100644
--- a/README.md
+++ b/README.md
@@ -179,8 +179,12 @@ for [Async Context](https://github.com/tc39/proposal-async-context) to solve thi
 
 ### `withStore`
 
+Adding a `getStore()` method to the workflow context, which returns a store object, each store is linked to the workflow
+context.
+
 ```ts
 import { withStore } from "fluere/middleware/store";
+
 const workflow = withStore(
   () => ({
     pendingTasks: new Set<Promise<unknown>>(),
@@ -203,7 +207,7 @@ const { getStore } = workflow.createContext();
 
 ### `withValidation`
 
-make first parameter of `handler` to be `sendEvent` and its type safe and runtime safe
+Make first parameter of `handler` to be `sendEvent` and its type safe and runtime safe
 when you create a workflow using `withValidation`.
 
 ```ts
@@ -236,6 +240,125 @@ workflow.handle([startEvent], (sendEvent, start) => {
 });
 ```
 
+### `withTraceEvents`
+
+Adds tracing capabilities to your workflow, allowing you to monitor/decorate handler and debug event flows easily.
+
+When enabled,
+it collects events based on the directed graph of the runtime and provide lifecycle hooks for each handler.
+
+```ts
+import { withTraceEvents, runOnce } from "fluere/middleware/trace-events";
+
+const workflow = withTraceEvents(createWorkflow());
+
+workflow.handle(
+  [messageEvent],
+  runOnce(() => {
+    console.log("This message handler will only run once");
+  }),
+);
+
+workflow.handle([startEvent], () => {
+  getContext().sendEvent(messageEvent.with());
+  getContext().sendEvent(messageEvent.with());
+});
+
+{
+  const { sendEvent } = workflow.createContext();
+  sendEvent(startEvent.with());
+  sendEvent(messageEvent.with());
+  // This message handler will only run once!
+}
+{
+  const { sendEvent } = workflow.createContext();
+  // For each new context, the decorator is isolated.
+  sendEvent(startEvent.with());
+  sendEvent(messageEvent.with());
+  // This message handler will only run once!
+}
+```
+
+#### `createHandlerDecorator`
+
+You can create your own handler decorator to modify the behavior of the handler.
+
+```ts
+import { createHandlerDecorator } from "fluere/middleware/trace-events";
+
+const noop: (...args: any[]) => void = function noop() {};
+export const runOnce = createHandlerDecorator({
+  debugLabel: "onceHook",
+  getInitialValue: () => false,
+  onBeforeHandler: (handler, handlerContext, tracked) =>
+    tracked ? noop : handler,
+  onAfterHandler: () => true,
+});
+```
+
+#### `HandlerContext`
+
+The `HandlerContext` includes the runtime information of the handler in the directed graph of the workflow.
+
+```ts
+type BaseHandlerContext = {
+  // ... some other properties are hidden
+  handler: Handler<WorkflowEvent<any>[], any>;
+  inputEvents: WorkflowEvent<any>[];
+  // events data that are accepted by the handler
+  inputs: WorkflowEventData<any>[];
+  // events data that are emitted by the handler
+  outputs: WorkflowEventData<any>[];
+
+  //#region linked list data structure
+  prev: HandlerContext;
+  next: Set<HandlerContext>;
+  root: HandlerContext;
+  //#endregion
+};
+
+type SyncHandlerContext = BaseHandlerContext & {
+  async: false;
+  pending: null;
+};
+
+type AsyncHandlerContext = BaseHandlerContext & {
+  async: true;
+  pending: Promise<WorkflowEventData<any> | void> | null;
+};
+
+type HandlerContext = AsyncHandlerContext | SyncHandlerContext;
+```
+
+For example, when you send two `startEvent` events, and send `messageEvent` twice (once in the handler and once in the global),
+the `HandlerContext` from root to leaf is:
+
+```ts
+let once = false;
+workflow.handle([startEvent], () => {
+  const { sendEvent } = getContext();
+  if (once) {
+    return;
+  }
+  once = true;
+  sendEvent(messageEvent.with());
+});
+const { sendEvent } = workflow.createContext();
+sendEvent(startEvent.with());
+sendEvent(startEvent.with());
+sendEvent(messageEvent.with());
+```
+
+```
+rootHandlerContext(0)
+  ├── startEventContext(0)
+  │   └── messageEventContext(0)
+  ├── startEventContext(1)
+  └── messageEventContext(1)
+```
+
+You can use any directed graph library to visualize the directed graph of the workflow.
+
 # LICENSE
 
 MIT
diff --git a/packages/fluere/src/core/event.ts b/packages/fluere/src/core/event.ts
index 092ee89..4845822 100644
--- a/packages/fluere/src/core/event.ts
+++ b/packages/fluere/src/core/event.ts
@@ -64,8 +64,6 @@ export const workflowEvent = <Data = void, DebugLabel extends string = string>(
   });
 
   event.toString = () => config?.debugLabel ?? `WorkflowEvent<${l1}>`;
-  Object.freeze(event);
-
   return event;
 };
 
diff --git a/packages/fluere/src/core/internal/context.ts b/packages/fluere/src/core/internal/context.ts
index 092fa0b..0c5d663 100644
--- a/packages/fluere/src/core/internal/context.ts
+++ b/packages/fluere/src/core/internal/context.ts
@@ -1,5 +1,40 @@
 import { createAsyncContext } from "fluere/async-context";
-import type { WorkflowEventData } from "../event";
+import type { WorkflowEvent, WorkflowEventData } from "../event";
+import type { Handler } from "./handler";
+
+type BaseHandlerContext = {
+  abortController: AbortController;
+  handler: Handler<WorkflowEvent<any>[], any>;
+  // events that are accepted by the handler
+  inputEvents: WorkflowEvent<any>[];
+  // events data that are accepted by the handler
+  inputs: WorkflowEventData<any>[];
+  // events data that are emitted by the handler
+  outputs: WorkflowEventData<any>[];
+
+  //#region linked list data structure
+  prev: HandlerContext;
+  next: Set<HandlerContext>;
+  root: HandlerContext;
+  //#endregion
+};
+
+type SyncHandlerContext = BaseHandlerContext & {
+  async: false;
+  pending: null;
+};
+
+type AsyncHandlerContext = BaseHandlerContext & {
+  async: true;
+  pending: Promise<WorkflowEventData<any> | void> | null;
+};
+
+export type HandlerContext = AsyncHandlerContext | SyncHandlerContext;
+
+export type ContextNext = (
+  context: HandlerContext,
+  next: (context: HandlerContext) => void,
+) => void;
 
 export interface WorkflowContext {
   get stream(): ReadableStream<WorkflowEventData<any>>;
@@ -9,13 +44,7 @@ export interface WorkflowContext {
   /**
    * @internal
    */
-  __internal__call_context: Set<
-    (
-      context: WorkflowContext,
-      inputs: WorkflowEventData<any>[],
-      next: () => void,
-    ) => void
-  >;
+  __internal__call_context: Set<ContextNext>;
 }
 
 export const _executorAsyncLocalStorage = createAsyncContext<WorkflowContext>();
@@ -23,7 +52,7 @@ export const _executorAsyncLocalStorage = createAsyncContext<WorkflowContext>();
 export function getContext(): WorkflowContext {
   const context = _executorAsyncLocalStorage.getStore();
   if (!context) {
-    throw new Error("No context found");
+    throw new Error("No current context found");
   }
   return context;
 }
diff --git a/packages/fluere/src/core/internal/executor.ts b/packages/fluere/src/core/internal/executor.ts
index caaaea9..b8f3c12 100644
--- a/packages/fluere/src/core/internal/executor.ts
+++ b/packages/fluere/src/core/internal/executor.ts
@@ -1,22 +1,12 @@
-import type {
-  Handler,
-  HandlerRef,
-  WorkflowEvent,
-  WorkflowEventData,
-} from "fluere";
+import type { Handler, WorkflowEvent, WorkflowEventData } from "fluere";
 import { flattenEvents, isEventData, isPromiseLike } from "../utils";
-import { _executorAsyncLocalStorage, type WorkflowContext } from "./context";
+import {
+  _executorAsyncLocalStorage,
+  type HandlerContext,
+  type WorkflowContext,
+} from "./context";
 import { createAsyncContext } from "fluere/async-context";
 
-type HandlerContext = {
-  abortController: AbortController;
-  handler: Handler<WorkflowEvent<any>[], any>;
-  inputs: WorkflowEventData<any>[];
-  outputs: WorkflowEventData<any>[];
-  prev: HandlerContext;
-  next: Set<HandlerContext>;
-};
-
 const handlerContextAsyncLocalStorage = createAsyncContext<HandlerContext>();
 
 const eventContextWeakMap = new WeakMap<
@@ -27,7 +17,7 @@ const eventContextWeakMap = new WeakMap<
 export type ExecutorParams = {
   listeners: ReadonlyMap<
     WorkflowEvent<any>[],
-    Set<HandlerRef<WorkflowEvent<any>[], any>>
+    Set<Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>>
   >;
 };
 
@@ -37,9 +27,10 @@ export const createContext = ({
   const queue: WorkflowEventData<any>[] = [];
   const runHandler = (
     handler: Handler<WorkflowEvent<any>[], any>,
+    inputEvents: WorkflowEvent<any>[],
     inputs: WorkflowEventData<any>[],
     parentContext: HandlerContext,
-  ) => {
+  ): void => {
     let handlerAbortController: AbortController;
     const handlerContext: HandlerContext = {
       get abortController() {
@@ -48,11 +39,20 @@ export const createContext = ({
         }
         return handlerAbortController;
       },
+      async:
+        "constructor" in handler
+          ? handler.constructor.name === "AsyncFunction"
+          : false,
+      pending: null,
       handler,
+      inputEvents,
       inputs,
       outputs: [],
       prev: parentContext,
       next: new Set(),
+      get root() {
+        return handlerRootContext;
+      },
     };
     handlerContext.prev.next.add(handlerContext);
     const workflowContext = createWorkflowContext(handlerContext);
@@ -66,11 +66,11 @@ export const createContext = ({
       _executorAsyncLocalStorage.run(workflowContext, () => {
         //#region middleware
         let i = 0;
-        const next = () => {
+        const next = (context: HandlerContext) => {
           if (i === cbs.length) {
             let result: any;
             try {
-              result = handler(...inputs);
+              result = context.handler(...context.inputs);
             } catch (error) {
               if (handlerAbortController ?? rootAbortController) {
                 (handlerAbortController ?? rootAbortController).abort(error);
@@ -81,6 +81,8 @@ export const createContext = ({
             }
             // return value is a special event
             if (isPromiseLike(result)) {
+              (handlerContext as any).async = true;
+              (handlerContext as any).pending = result;
               result.then((event) => {
                 if (isEventData(event)) {
                   workflowContext.sendEvent(event);
@@ -93,10 +95,10 @@ export const createContext = ({
           const cb = cbs[i];
           if (cb) {
             i++;
-            cb(workflowContext, inputs, next);
+            cb(context, next);
           }
         };
-        next();
+        next(handlerContext);
         //#endregion
       });
     });
@@ -108,13 +110,13 @@ export const createContext = ({
         const inputs = flattenEvents(events, queueSnapshot);
         return inputs.length === events.length;
       })
-      .map(([events, refs]) => {
+      .map(([events, handlers]) => {
         const inputs = flattenEvents(events, queueSnapshot);
         inputs.forEach((input) => {
           queue.splice(queue.indexOf(input), 1);
         });
-        for (const ref of refs) {
-          runHandler(ref.handler, inputs, handlerContext);
+        for (const handler of handlers) {
+          runHandler(handler, events, inputs, handlerContext);
         }
       });
   };
@@ -163,11 +165,17 @@ export const createContext = ({
       }
       return rootAbortController;
     },
+    async: false,
+    pending: null,
+    inputEvents: [],
     inputs: [],
     outputs: [],
     handler: null!,
     prev: null!,
     next: new Set(),
+    get root() {
+      return handlerRootContext;
+    },
   };
 
   const rootWorkflowContext = createWorkflowContext(handlerRootContext);
diff --git a/packages/fluere/src/core/workflow.ts b/packages/fluere/src/core/workflow.ts
index 48d2ee6..6dc2aa5 100644
--- a/packages/fluere/src/core/workflow.ts
+++ b/packages/fluere/src/core/workflow.ts
@@ -1,7 +1,7 @@
-import { type WorkflowEvent } from "./event";
+import { type WorkflowEvent, type WorkflowEventData } from "./event";
 import { createContext } from "./internal/executor";
-import { type Handler, type HandlerRef } from "./internal/handler";
-import type { WorkflowContext } from "./internal/context";
+import { type Handler } from "./internal/handler";
+import { getContext, type WorkflowContext } from "./internal/context";
 
 export type Workflow = {
   handle<
@@ -10,7 +10,7 @@ export type Workflow = {
   >(
     accept: AcceptEvents,
     handler: Handler<AcceptEvents, Result>,
-  ): HandlerRef<AcceptEvents, Result>;
+  ): void;
   createContext(): WorkflowContext;
 };
 
@@ -18,7 +18,7 @@ export function createWorkflow(): Workflow {
   const config = {
     steps: new Map<
       WorkflowEvent<any>[],
-      Set<HandlerRef<WorkflowEvent<any>[], any>>
+      Set<Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>>
     >(),
   };
 
@@ -29,43 +29,31 @@ export function createWorkflow(): Workflow {
     >(
       accept: AcceptEvents,
       handler: Handler<AcceptEvents, Result>,
-    ): HandlerRef<AcceptEvents, Result> => {
+    ): void => {
+      // smoke test to check if we are outside the context
+      let success = false;
+      try {
+        getContext();
+        console.error("Calling handle inside of context is not allowed.");
+        success = true;
+      } catch {}
+      if (success) {
+        throw new Error("Calling handle inside of context is not allowed.");
+      }
       if (config.steps.has(accept)) {
         const set = config.steps.get(accept) as Set<
-          HandlerRef<AcceptEvents, Result>
+          Handler<AcceptEvents, Result>
         >;
-        const ref: HandlerRef<AcceptEvents, Result> = {
-          get handler() {
-            return handler;
-          },
-          unsubscribe: () => {
-            set.delete(ref);
-            if (set.size === 0) {
-              config.steps.delete(accept);
-            }
-          },
-        };
-        set.add(ref);
-        return ref;
+        set.add(handler);
       } else {
-        const set = new Set<HandlerRef<AcceptEvents, Result>>();
-        const ref: HandlerRef<AcceptEvents, Result> = {
-          get handler() {
-            return handler;
-          },
-          unsubscribe: () => {
-            set.delete(ref);
-            if (set.size === 0) {
-              config.steps.delete(accept);
-            }
-          },
-        };
-        set.add(ref);
+        const set = new Set<Handler<AcceptEvents, Result>>();
+        set.add(handler);
         config.steps.set(
           accept,
-          set as Set<HandlerRef<WorkflowEvent<any>[], any>>,
+          set as Set<
+            Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>
+          >,
         );
-        return ref;
       }
     },
     createContext() {
diff --git a/packages/fluere/src/middleware/store.ts b/packages/fluere/src/middleware/store.ts
index d132f9f..5794980 100644
--- a/packages/fluere/src/middleware/store.ts
+++ b/packages/fluere/src/middleware/store.ts
@@ -1,27 +1,51 @@
 import { type WorkflowContext, type Workflow, getContext } from "fluere";
 
-export function withStore<T, Input extends void>(
+export function withStore<
+  T,
+  Input extends void,
+  WorkflowLike extends {
+    createContext(): WorkflowContext;
+  } = {
+    createContext(): WorkflowContext;
+  },
+>(
   createStore: () => T,
-  workflow: Workflow,
-): Omit<Workflow, "createContext"> & {
+  workflow: WorkflowLike,
+): Omit<WorkflowLike, "createContext"> & {
   createContext(): WorkflowContext & {
     getStore(): T;
   };
   getStore(): T;
 };
-export function withStore<T, Input>(
+export function withStore<
+  T,
+  Input,
+  WorkflowLike extends {
+    createContext(): WorkflowContext;
+  } = {
+    createContext(): WorkflowContext;
+  },
+>(
   createStore: (input: Input) => T,
-  workflow: Workflow,
-): Omit<Workflow, "createContext"> & {
+  workflow: WorkflowLike,
+): Omit<WorkflowLike, "createContext"> & {
   createContext(input: Input): WorkflowContext & {
     getStore(): T;
   };
   getStore(): T;
 };
-export function withStore<T, Input>(
+export function withStore<
+  T,
+  Input,
+  WorkflowLike extends {
+    createContext(): WorkflowContext;
+  } = {
+    createContext(): WorkflowContext;
+  },
+>(
   createStore: (input: Input) => T,
-  workflow: Workflow,
-): Omit<Workflow, "createContext"> & {
+  workflow: WorkflowLike,
+): Omit<WorkflowLike, "createContext"> & {
   createContext(input: Input): WorkflowContext & {
     getStore(): T;
   };
@@ -40,9 +64,9 @@ export function withStore<T, Input>(
       const context = workflow.createContext() as WorkflowContext & {
         getStore: () => T;
       };
-      context.__internal__call_context.add((context, _, next) => {
-        (context as any).getStore = () => currentStore;
-        next();
+      context.__internal__call_context.add((_, next) => {
+        (getContext() as any).getStore = () => currentStore;
+        next(_);
       });
       (context as any).getStore = () => currentStore;
       return context;
diff --git a/packages/fluere/src/middleware/trace-events.ts b/packages/fluere/src/middleware/trace-events.ts
new file mode 100644
index 0000000..0b12689
--- /dev/null
+++ b/packages/fluere/src/middleware/trace-events.ts
@@ -0,0 +1,152 @@
+import type {
+  Handler,
+  Workflow,
+  WorkflowContext,
+  WorkflowEvent,
+  WorkflowEventData,
+} from "fluere";
+import { isPromiseLike } from "../core/utils";
+import {
+  createHandlerDecorator,
+  decoratorRegistry,
+} from "./trace-events/create-handler-decorator";
+import { runOnce } from "./trace-events/run-once";
+
+type TracingContext = Record<string, unknown>;
+
+const tracingWeakMap = new WeakMap<
+  WorkflowContext,
+  WeakMap<
+    WorkflowEvent<any>[],
+    WeakMap<
+      Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>,
+      TracingContext
+    >
+  >
+>();
+
+export type HandlerRef<
+  AcceptEvents extends WorkflowEvent<any>[],
+  Result extends ReturnType<WorkflowEvent<any>["with"]> | void,
+  Fn extends Handler<AcceptEvents, Result>,
+> = {
+  get handler(): Fn;
+};
+
+export function withTraceEvents<
+  WorkflowLike extends {
+    handle<
+      const AcceptEvents extends WorkflowEvent<any>[],
+      Result extends ReturnType<WorkflowEvent<any>["with"]> | void,
+    >(
+      accept: AcceptEvents,
+      handler: Handler<AcceptEvents, Result>,
+    ): void;
+    createContext(): WorkflowContext;
+  },
+>(
+  workflow: WorkflowLike,
+): Omit<WorkflowLike, "handle"> & {
+  handle<
+    const AcceptEvents extends WorkflowEvent<any>[],
+    Result extends ReturnType<WorkflowEvent<any>["with"]> | void,
+    Fn extends Handler<AcceptEvents, Result>,
+  >(
+    accept: AcceptEvents,
+    handler: Fn,
+  ): HandlerRef<AcceptEvents, Result, Fn>;
+  createContext(): WorkflowContext;
+} {
+  return {
+    ...workflow,
+    handle: <
+      const AcceptEvents extends WorkflowEvent<any>[],
+      Result extends ReturnType<WorkflowEvent<any>["with"]> | void,
+      Fn extends Handler<AcceptEvents, Result>,
+    >(
+      accept: AcceptEvents,
+      handler: Fn,
+    ): HandlerRef<AcceptEvents, Result, Fn> => {
+      workflow.handle(accept, handler);
+      return {
+        get handler(): Fn {
+          return handler;
+        },
+      };
+    },
+    createContext(): WorkflowContext {
+      const context = workflow.createContext();
+      tracingWeakMap.set(context, new WeakMap());
+      context.__internal__call_context.add((handlerContext, next) => {
+        const inputEvents = handlerContext.inputEvents;
+        const handlersWeakMap = tracingWeakMap.get(context)!;
+        if (!handlersWeakMap.has(inputEvents)) {
+          handlersWeakMap.set(inputEvents, new WeakMap());
+        }
+        const handlerWeakMap = handlersWeakMap.get(inputEvents)!;
+
+        const originalHandler = handlerContext.handler;
+        let finalHandler = originalHandler;
+        let handlerMiddleware: Handler<
+          WorkflowEvent<any>[],
+          WorkflowEventData<any> | void
+        >;
+        if (!handlerWeakMap) {
+          throw new Error(
+            "Handler context is not defined, this should not happen. Please report this issue with a reproducible example.",
+          );
+        }
+        const tracingContext: TracingContext =
+          handlerWeakMap.get(originalHandler) ?? {};
+        if (!handlerWeakMap.has(originalHandler)) {
+          handlerWeakMap.set(originalHandler, tracingContext);
+        }
+
+        const onAfterHandlers = [] as (() => void)[];
+        const onBeforeHandlers = [] as ((
+          nextHandler: Handler<
+            WorkflowEvent<any>[],
+            WorkflowEventData<any> | void
+          >,
+        ) => Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>)[];
+        handlerMiddleware = (...args) => {
+          const result = onBeforeHandlers.reduce((next, cb) => {
+            return cb(next);
+          }, finalHandler)(...args);
+          if (isPromiseLike(result)) {
+            return result.then(() => {
+              onAfterHandlers.forEach((cb) => {
+                cb();
+              });
+            });
+          } else {
+            onAfterHandlers.forEach((cb) => {
+              cb();
+            });
+            return result;
+          }
+        };
+        [...decoratorRegistry].forEach(
+          ([name, { getInitialValue, onAfterHandler, onBeforeHandler }]) => {
+            if (!tracingContext[name]) {
+              tracingContext[name] = getInitialValue();
+            }
+            onBeforeHandlers.push((next) =>
+              onBeforeHandler(next, handlerContext, tracingContext[name]),
+            );
+            onAfterHandlers.push(() => {
+              tracingContext[name] = onAfterHandler(tracingContext[name]);
+            });
+          },
+        );
+        next({
+          ...handlerContext,
+          handler: handlerMiddleware,
+        });
+      });
+      return context;
+    },
+  };
+}
+
+export { createHandlerDecorator, runOnce };
diff --git a/packages/fluere/src/middleware/trace-events/create-handler-decorator.ts b/packages/fluere/src/middleware/trace-events/create-handler-decorator.ts
new file mode 100644
index 0000000..652e5c2
--- /dev/null
+++ b/packages/fluere/src/middleware/trace-events/create-handler-decorator.ts
@@ -0,0 +1,46 @@
+import type { Handler, WorkflowEvent, WorkflowEventData } from "fluere";
+import type { HandlerContext } from "../../core/internal/context";
+
+const namespace = "decorator" as const;
+
+let counter = 0;
+
+export const decoratorRegistry = new Map<
+  string,
+  {
+    debugLabel: string;
+    getInitialValue: () => any;
+    onBeforeHandler: (
+      handler: Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>,
+      handlerContext: Readonly<HandlerContext>,
+      metadata: any,
+    ) => Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>;
+    onAfterHandler: (metadata: any) => any;
+  }
+>();
+
+export function createHandlerDecorator<Metadata>(config: {
+  debugLabel?: string;
+  getInitialValue: () => Metadata;
+  onBeforeHandler: (
+    handler: Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>,
+    handlerContext: HandlerContext,
+    metadata: Metadata,
+  ) => Handler<WorkflowEvent<any>[], WorkflowEventData<any> | void>;
+  onAfterHandler: (metadata: Metadata) => Metadata;
+}) {
+  const uid = `${namespace}:${counter++}`;
+  decoratorRegistry.set(uid, {
+    debugLabel: config.debugLabel ?? uid,
+    getInitialValue: config.getInitialValue,
+    onAfterHandler: config.onAfterHandler,
+    onBeforeHandler: config.onBeforeHandler,
+  });
+  return function <
+    const AcceptEvents extends WorkflowEvent<any>[],
+    Result extends ReturnType<WorkflowEvent<any>["with"]> | void,
+    Fn extends Handler<AcceptEvents, Result>,
+  >(handler: Fn) {
+    return handler;
+  };
+}
diff --git a/packages/fluere/src/middleware/trace-events/run-once.ts b/packages/fluere/src/middleware/trace-events/run-once.ts
new file mode 100644
index 0000000..aaa778f
--- /dev/null
+++ b/packages/fluere/src/middleware/trace-events/run-once.ts
@@ -0,0 +1,10 @@
+import { createHandlerDecorator } from "./create-handler-decorator";
+
+const noop: (...args: any[]) => void = function noop() {};
+
+export const runOnce = createHandlerDecorator({
+  debugLabel: "onceHook",
+  getInitialValue: () => false,
+  onBeforeHandler: (handler, _, tracked) => (tracked ? noop : handler),
+  onAfterHandler: () => true,
+});
diff --git a/packages/fluere/src/middleware/validation.ts b/packages/fluere/src/middleware/validation.ts
index ad62cee..3bd6c88 100644
--- a/packages/fluere/src/middleware/validation.ts
+++ b/packages/fluere/src/middleware/validation.ts
@@ -2,7 +2,6 @@ import {
   type WorkflowContext,
   getContext,
   type Handler,
-  type HandlerRef,
   type Workflow,
   type WorkflowEvent,
   type WorkflowEventData,
@@ -44,7 +43,7 @@ export type WithValidationWorkflow<
   >(
     accept: AcceptEvents,
     handler: ValidationHandler<Validation, AcceptEvents, Result>,
-  ): HandlerRef<AcceptEvents, Result>;
+  ): void;
   createContext(): WorkflowContext;
 };
 
@@ -66,22 +65,18 @@ export function withValidation<
     const store = getContext();
     const originalSendEvent = store.sendEvent;
     return (...inputs: WorkflowEventData<any>[]) => {
-      let matched = false;
       for (let i = 0; i < outputs.length; i++) {
         const output = outputs[i]!;
         if (output.length === inputs.length) {
           if (output.every((e, idx) => e.include(inputs[idx]))) {
-            matched = true;
-            break;
+            return originalSendEvent(...inputs);
           }
         }
       }
-      if (matched) {
-        console.warn(
-          "Invalid input detected [%s]",
-          inputs.map((i) => i.data).join(", "),
-        );
-      }
+      console.warn(
+        "Invalid input detected [%s]",
+        inputs.map((i) => i.data).join(", "),
+      );
       return originalSendEvent(...inputs);
     };
   };
@@ -102,9 +97,11 @@ export function withValidation<
     },
     createContext(): WorkflowContext {
       const context = workflow.createContext();
-      context.__internal__call_context.add((context, inputs, next) => {
-        (context as any).safeSendEvent = createSafeSendEvent(...inputs);
-        next();
+      context.__internal__call_context.add((context, next) => {
+        (getContext() as any).safeSendEvent = createSafeSendEvent(
+          ...context.inputs,
+        );
+        next(context);
       });
       return context;
     },
diff --git a/packages/fluere/src/util/zod.ts b/packages/fluere/src/util/zod.ts
index a95a85c..9862ee2 100644
--- a/packages/fluere/src/util/zod.ts
+++ b/packages/fluere/src/util/zod.ts
@@ -5,16 +5,15 @@ import {
   type WorkflowEventConfig,
 } from "fluere";
 
-export const zodEvent = <T>(
+export const zodEvent = <T, DebugLabel extends string>(
   schema: z.ZodType<T>,
-  config?: WorkflowEventConfig,
-): WorkflowEvent<T> => {
-  const event = workflowEvent<T>(config);
-  return {
-    include: event.include,
-    with(data: T) {
-      schema.parse(data);
-      return event.with(data);
-    },
-  } as unknown as WorkflowEvent<T>;
+  config?: WorkflowEventConfig<DebugLabel>,
+): WorkflowEvent<T, DebugLabel> => {
+  const event = workflowEvent<T, DebugLabel>(config);
+  const originalWith = event.with;
+  event.with = (data: T) => {
+    schema.parse(data);
+    return originalWith(data);
+  };
+  return event;
 };
diff --git a/packages/fluere/tests/full-workflow.spec.ts b/packages/fluere/tests/full-workflow.spec.ts
new file mode 100644
index 0000000..22afc61
--- /dev/null
+++ b/packages/fluere/tests/full-workflow.spec.ts
@@ -0,0 +1,79 @@
+import { describe, test, expect } from "vitest";
+import { createWorkflow, eventSource, type WorkflowEvent } from "fluere";
+import { withStore } from "fluere/middleware/store";
+import { withTraceEvents } from "fluere/middleware/trace-events";
+import { withValidation } from "fluere/middleware/validation";
+import { zodEvent } from "fluere/util/zod";
+import { z } from "zod";
+import { webcrypto } from "node:crypto";
+
+describe("full workflow middleware", () => {
+  const createFullWorkflow = <
+    const Validation extends [
+      inputs: WorkflowEvent<any>[],
+      outputs: WorkflowEvent<any>[],
+    ][],
+    T,
+    Input,
+  >(
+    validation: Validation,
+    createStore: (input: Input) => T,
+  ) => {
+    return withStore(
+      createStore,
+      withValidation<Validation>(withTraceEvents(createWorkflow()), validation),
+    );
+  };
+  test("type check", () => {
+    const startEvent = zodEvent(z.string(), {
+      debugLabel: "start",
+    });
+    const messageEvent = zodEvent(z.string(), {
+      debugLabel: "message",
+    });
+    const stopEvent = zodEvent(z.string(), {
+      debugLabel: "stop",
+    });
+    const workflow = createFullWorkflow(
+      [[[startEvent], [stopEvent]]],
+      () => ({}),
+    );
+    workflow.handle([startEvent], (sendEvent, events) => {
+      // @ts-expect-error
+      sendEvent(messageEvent.with());
+      sendEvent(stopEvent.with(""));
+    });
+  });
+
+  test("basic", async () => {
+    const startEvent = zodEvent(z.string(), {
+      debugLabel: "start",
+    });
+    const stopEvent = zodEvent(z.string(), {
+      debugLabel: "stop",
+    });
+    const workflow = createFullWorkflow(
+      [[[startEvent], [stopEvent]]],
+      (id: string) => ({
+        id,
+      }),
+    );
+    workflow.handle([startEvent], (sendEvent, start) => {
+      expect(start.data).toBe("start");
+      sendEvent(stopEvent.with(workflow.getStore().id));
+    });
+
+    const id = webcrypto.randomUUID();
+    const { sendEvent, stream } = workflow.createContext(id);
+    const events = [];
+    sendEvent(startEvent.with("start"));
+    for await (const event of stream) {
+      events.push(event);
+      if (stopEvent.include(event)) {
+        break;
+      }
+    }
+    expect(events.length).toBe(2);
+    expect(events.map(eventSource)).toEqual([startEvent, stopEvent]);
+  });
+});
diff --git a/packages/fluere/tests/with-trace-events.spec.ts b/packages/fluere/tests/with-trace-events.spec.ts
new file mode 100644
index 0000000..50c04ec
--- /dev/null
+++ b/packages/fluere/tests/with-trace-events.spec.ts
@@ -0,0 +1,110 @@
+import { describe, test, vi, expectTypeOf, type Mock, expect } from "vitest";
+import { createWorkflow, workflowEvent } from "fluere";
+import {
+  withTraceEvents,
+  runOnce,
+  createHandlerDecorator,
+} from "fluere/middleware/trace-events";
+
+describe("with trace events", () => {
+  test("runOnce", () => {
+    const workflow = withTraceEvents(createWorkflow());
+    const startEvent = workflowEvent();
+    const ref = workflow.handle([startEvent], vi.fn(runOnce(() => {})));
+    expectTypeOf(ref.handler).toEqualTypeOf<Mock<() => void>>();
+    {
+      const { sendEvent } = workflow.createContext();
+      expect(ref.handler).not.toHaveBeenCalled();
+      sendEvent(startEvent.with());
+      expect(ref.handler).toBeCalledTimes(1);
+      sendEvent(startEvent.with());
+      expect(ref.handler).toBeCalledTimes(1);
+    }
+    ref.handler.mockReset();
+    {
+      const { sendEvent } = workflow.createContext();
+      expect(ref.handler).not.toHaveBeenCalled();
+      sendEvent(startEvent.with());
+      expect(ref.handler).toBeCalledTimes(1);
+    }
+  });
+
+  test("example: no parallel", async () => {
+    const workflow = withTraceEvents(createWorkflow());
+    const startEvent = workflowEvent();
+    type Metadata = {
+      running: boolean;
+    };
+    const getInitialValue = vi.fn(
+      (): Metadata => ({
+        running: false,
+      }),
+    );
+    const noParallel = createHandlerDecorator<Metadata>({
+      getInitialValue,
+      onAfterHandler: () => ({
+        running: false,
+      }),
+      onBeforeHandler: (h, handlerContext, metadata) => async () => {
+        metadata.running = true;
+        const root = handlerContext.root;
+        const similarContexts = [];
+        const queue = [root];
+        while (queue.length > 0) {
+          const current = queue.pop();
+          if (!current) {
+            break;
+          }
+          if (current.handler === handlerContext.handler) {
+            similarContexts.push(current);
+          }
+          queue.push(...current.next);
+        }
+        const asyncContexts = similarContexts.filter((c) => c.async);
+        for (const context of asyncContexts) {
+          await context.pending;
+        }
+        return h();
+      },
+    });
+    let count = 0;
+    let resolveNext: () => void = null!;
+    let p = new Promise<void>((_resolve) => {
+      resolveNext = _resolve;
+    });
+    let result: number[] = [];
+    const ref = workflow.handle(
+      [startEvent],
+      vi.fn(
+        noParallel(async () => {
+          count++;
+          const curr = count;
+          await p.then(() => {
+            result.push(curr);
+            p = new Promise<void>((_resolve) => {
+              resolveNext = _resolve;
+            });
+          });
+        }),
+      ),
+    );
+    expectTypeOf(ref.handler).toEqualTypeOf<Mock<() => Promise<void>>>();
+    const { sendEvent } = workflow.createContext();
+    expect(ref.handler).not.toHaveBeenCalled();
+    sendEvent(startEvent.with());
+    sendEvent(startEvent.with());
+    sendEvent(startEvent.with());
+    expect(ref.handler).toBeCalledTimes(1);
+    expect(result).toEqual([]);
+    resolveNext();
+    vi.waitFor(() => expect(result).toEqual([1]));
+    resolveNext();
+    vi.waitFor(() => expect(result).toEqual([1, 2]));
+    resolveNext();
+    vi.waitFor(() => expect(result).toEqual([1, 2, 3]));
+    sendEvent(startEvent.with());
+    vi.waitFor(() => expect(result).toEqual([1, 2, 3]));
+    resolveNext();
+    vi.waitFor(() => expect(result).toEqual([1, 2, 3, 4]));
+  });
+});
diff --git a/packages/fluere/tests/with-validation.spec.ts b/packages/fluere/tests/with-validation.spec.ts
index b4cb7d0..48775d7 100644
--- a/packages/fluere/tests/with-validation.spec.ts
+++ b/packages/fluere/tests/with-validation.spec.ts
@@ -13,12 +13,18 @@ describe("with directed graph", () => {
   });
 
   test("basic", async () => {
-    const startEvent = workflowEvent<void, "start">();
+    const startEvent = workflowEvent<void, "start">({
+      debugLabel: "start",
+    });
     const nonEvent = workflowEvent<number, "non">({
       debugLabel: "non",
     });
-    const parseEvent = workflowEvent<string, "parse">();
-    const stopEvent = workflowEvent<number, "stop">();
+    const parseEvent = workflowEvent<string, "parse">({
+      debugLabel: "parse",
+    });
+    const stopEvent = workflowEvent<number, "stop">({
+      debugLabel: "stop",
+    });
     const workflow = withValidation(createWorkflow(), [
       [[startEvent], [stopEvent]],
       [[startEvent], [parseEvent, parseEvent]],
@@ -39,11 +45,17 @@ describe("with directed graph", () => {
     sendEvent(startEvent.with());
     await find(stream, stopEvent);
     expect(fn).toBeCalled();
-    expect(consoleWarnMock).toHaveBeenCalledOnce();
-    expect(consoleWarnMock).toHaveBeenLastCalledWith(
+    expect(consoleWarnMock).toBeCalledTimes(2);
+    expect(consoleWarnMock).toHaveBeenNthCalledWith(
+      1,
       "Invalid input detected [%s]",
       "1",
     );
+    expect(consoleWarnMock).toHaveBeenNthCalledWith(
+      2,
+      "Invalid input detected [%s]",
+      "",
+    );
   });
 
   test("promise", async () => {
diff --git a/packages/fluere/tsconfig.browser.json b/packages/fluere/tsconfig.browser.json
index 03eec35..b52b110 100644
--- a/packages/fluere/tsconfig.browser.json
+++ b/packages/fluere/tsconfig.browser.json
@@ -6,7 +6,10 @@
     "paths": {
       "fluere": ["./src/core/index.ts"],
       "fluere/stream": ["./src/stream/index.ts"],
-      "fluere/async-context": ["./src/async-context/index.browser.ts"]
+      "fluere/async-context": ["./src/async-context/index.browser.ts"],
+      "fluere/interrupter/*": ["./src/interrupter/*.ts"],
+      "fluere/middleware/*": ["./src/middleware/*.ts"],
+      "fluere/util/*": ["./src/util/*.ts"]
     }
   },
   "include": ["./src"]
diff --git a/packages/fluere/tsconfig.json b/packages/fluere/tsconfig.json
index c90c3b0..7dfe6e3 100644
--- a/packages/fluere/tsconfig.json
+++ b/packages/fluere/tsconfig.json
@@ -21,8 +21,8 @@
       "fluere/async-context": ["./src/async-context/index.ts"],
       "fluere/interrupter/*": ["./src/interrupter/*.ts"],
       "fluere/middleware/*": ["./src/middleware/*.ts"],
-      "fluere/util": ["./src/util/index.ts"],
-      "fluere/stream": ["./src/stream/index.ts"],
+      "fluere/util/*": ["./src/util/*.ts"],
+      "fluere/stream": ["./src/stream/index.ts"]
     }
   },
   "include": ["./src"],
diff --git a/vitest.workspace.ts b/vitest.workspace.ts
index ff15a62..c1efc9a 100644
--- a/vitest.workspace.ts
+++ b/vitest.workspace.ts
@@ -1,3 +1 @@
-export default [
-  'packages/*',
-]
+export default ["packages/*"];