diff --git a/.changeset/fix-concurrent-wait-completed.md b/.changeset/fix-concurrent-wait-completed.md
new file mode 100644
index 0000000000..deed1e0669
--- /dev/null
+++ b/.changeset/fix-concurrent-wait-completed.md
@@ -0,0 +1,5 @@
+---
+'@workflow/world-local': patch
+---
+
+Fix concurrent `wait_completed` race condition that caused duplicate events and `Unconsumed event` errors during replay
diff --git a/.changeset/fix-wait-completed-event-refetch.md b/.changeset/fix-wait-completed-event-refetch.md
new file mode 100644
index 0000000000..23abaddfb8
--- /dev/null
+++ b/.changeset/fix-wait-completed-event-refetch.md
@@ -0,0 +1,6 @@
+---
+'@workflow/core': patch
+'workflow': patch
+---
+
+Re-fetch event log on `wait_completed` 409 conflict to ensure correct event ordering
diff --git a/packages/core/src/runtime.ts b/packages/core/src/runtime.ts
index ecbbfc85b2..fcbb1e33f1 100644
--- a/packages/core/src/runtime.ts
+++ b/packages/core/src/runtime.ts
@@ -218,7 +218,7 @@ export function workflowEntrypoint(
                 }
 
                 // Load all events into memory before running
-                const events = await getAllWorkflowRunEvents(workflowRun.runId);
+                let events = await getAllWorkflowRunEvents(workflowRun.runId);
 
                 // Check for any elapsed waits and create wait_completed events
                 const now = Date.now();
@@ -245,7 +245,11 @@ export function workflowEntrypoint(
                     correlationId: e.correlationId,
                   }));
 
-                // Create all wait_completed events
+                // Create all wait_completed events.
+                // If any creation returns 409, a concurrent invocation already
+                // created the event. Re-fetch the full event log to get the
+                // authoritative ordering rather than appending locally.
+                let needsRefetch = false;
                 for (const waitEvent of waitsToComplete) {
                   try {
                     const result = await world.events.create(runId, waitEvent);
@@ -257,12 +261,19 @@ export function workflowEntrypoint(
                         workflowRunId: runId,
                         correlationId: waitEvent.correlationId,
                       });
+                      needsRefetch = true;
                       continue;
                     }
                     throw err;
                   }
                 }
 
+                // Re-fetch the event log if a concurrent invocation created
+                // events we don't have locally, ensuring correct ordering.
+                if (needsRefetch) {
+                  events = await getAllWorkflowRunEvents(workflowRun.runId);
+                }
+
                 // Resolve the encryption key for this run's deployment
                 const rawKey =
                   await world.getEncryptionKeyForRun?.(workflowRun);
diff --git a/packages/world-local/src/storage.test.ts b/packages/world-local/src/storage.test.ts
index 641ad2c623..46db0205dd 100644
--- a/packages/world-local/src/storage.test.ts
+++ b/packages/world-local/src/storage.test.ts
@@ -12,9 +12,11 @@ import { afterEach, beforeEach, describe, expect, it } from 'vitest';
 import { writeJSON } from './fs.js';
 import { createStorage } from './storage.js';
 import {
+  completeWait,
   createHook,
   createRun,
   createStep,
+  createWait,
   disposeHook,
   updateRun,
   updateStep,
@@ -2666,6 +2668,102 @@ describe('Storage', () => {
     });
   });
 
+  describe('waits', () => {
+    it('should create and complete a wait', async () => {
+      const run = await createRun(storage, {
+        deploymentId: 'dep-1',
+        workflowName: 'wf-1',
+        input: new Uint8Array(),
+      });
+      await updateRun(storage, run.runId, 'run_started');
+
+      const wait = await createWait(storage, run.runId, {
+        waitId: 'wait_001',
+        resumeAt: new Date('2099-01-01'),
+      });
+      expect(wait.status).toBe('waiting');
+
+      const completed = await completeWait(storage, run.runId, 'wait_001');
+      expect(completed.status).toBe('completed');
+    });
+
+    it('should reject duplicate wait_created for the same correlationId', async () => {
+      const run = await createRun(storage, {
+        deploymentId: 'dep-1',
+        workflowName: 'wf-1',
+        input: new Uint8Array(),
+      });
+      await updateRun(storage, run.runId, 'run_started');
+
+      await createWait(storage, run.runId, {
+        waitId: 'wait_dup',
+        resumeAt: new Date('2099-01-01'),
+      });
+
+      await expect(
+        createWait(storage, run.runId, {
+          waitId: 'wait_dup',
+          resumeAt: new Date('2099-01-01'),
+        })
+      ).rejects.toThrow(/already exists/i);
+    });
+
+    it('should reject duplicate wait_completed for the same correlationId', async () => {
+      const run = await createRun(storage, {
+        deploymentId: 'dep-1',
+        workflowName: 'wf-1',
+        input: new Uint8Array(),
+      });
+      await updateRun(storage, run.runId, 'run_started');
+
+      await createWait(storage, run.runId, {
+        waitId: 'wait_once',
+        resumeAt: new Date('2099-01-01'),
+      });
+
+      await completeWait(storage, run.runId, 'wait_once');
+
+      // Second completion should be rejected with 409
+      await expect(
+        completeWait(storage, run.runId, 'wait_once')
+      ).rejects.toThrow(/already completed/i);
+    });
+
+    it('should reject concurrent wait_completed for the same correlationId', async () => {
+      const run = await createRun(storage, {
+        deploymentId: 'dep-1',
+        workflowName: 'wf-1',
+        input: new Uint8Array(),
+      });
+      await updateRun(storage, run.runId, 'run_started');
+
+      await createWait(storage, run.runId, {
+        waitId: 'wait_race',
+        resumeAt: new Date('2099-01-01'),
+      });
+
+      // Simulate two concurrent completions racing
+      const results = await Promise.allSettled([
+        completeWait(storage, run.runId, 'wait_race'),
+        completeWait(storage, run.runId, 'wait_race'),
+      ]);
+
+      const fulfilled = results.filter((r) => r.status === 'fulfilled');
+      const rejected = results.filter((r) => r.status === 'rejected');
+
+      // Exactly one should succeed, one should fail with 409
+      expect(fulfilled).toHaveLength(1);
+      expect(rejected).toHaveLength(1);
+      expect((rejected[0] as PromiseRejectedResult).reason).toBeInstanceOf(
+        WorkflowAPIError
+      );
+      expect(
+        ((rejected[0] as PromiseRejectedResult).reason as WorkflowAPIError)
+          .status
+      ).toBe(409);
+    });
+  });
+
   describe('custom runId validation', () => {
     const runCreatedEvent = {
       eventType: 'run_created' as const,
diff --git a/packages/world-local/src/storage/events-storage.ts b/packages/world-local/src/storage/events-storage.ts
index 56d636aed0..03616cb24a 100644
--- a/packages/world-local/src/storage/events-storage.ts
+++ b/packages/world-local/src/storage/events-storage.ts
@@ -718,8 +718,23 @@ export function createEventsStorage(
           wait
         );
       } else if (data.eventType === 'wait_completed') {
-        // wait_completed: Transitions wait to 'completed', rejects duplicates
+        // wait_completed: Transitions wait to 'completed', rejects duplicates.
+        // Uses writeExclusive on a lock file to atomically prevent concurrent
+        // invocations from both completing the same wait (TOCTOU race).
         const waitCompositeKey = `${effectiveRunId}-${data.correlationId}`;
+        const lockPath = taggedPath(
+          basedir,
+          'waits',
+          `${waitCompositeKey}.completed`,
+          tag
+        );
+        const claimed = await writeExclusive(lockPath, '');
+        if (!claimed) {
+          throw new WorkflowAPIError(
+            `Wait "${data.correlationId}" already completed`,
+            { status: 409 }
+          );
+        }
         const existingWait = await readJSONWithFallback(
           basedir,
           'waits',
@@ -732,12 +747,6 @@ export function createEventsStorage(
             status: 404,
           });
         }
-        if (existingWait.status === 'completed') {
-          throw new WorkflowAPIError(
-            `Wait "${data.correlationId}" already completed`,
-            { status: 409 }
-          );
-        }
         wait = {
           ...existingWait,
           status: 'completed',
diff --git a/packages/world-local/src/test-helpers.ts b/packages/world-local/src/test-helpers.ts
index 684ee2753a..eab7d589a0 100644
--- a/packages/world-local/src/test-helpers.ts
+++ b/packages/world-local/src/test-helpers.ts
@@ -3,6 +3,7 @@ import type {
   SerializedData,
   Step,
   Storage,
+  Wait,
   WorkflowRun,
 } from '@workflow/world';
 import { SPEC_VERSION_CURRENT } from '@workflow/world';
@@ -139,3 +140,45 @@ export async function disposeHook(
     correlationId: hookId,
   });
 }
+
+/**
+ * Create a new wait through the wait_created event.
+ */
+export async function createWait(
+  storage: Storage,
+  runId: string,
+  data: {
+    waitId: string;
+    resumeAt: Date;
+  }
+): Promise<Wait> {
+  const result = await storage.events.create(runId, {
+    eventType: 'wait_created',
+    specVersion: SPEC_VERSION_CURRENT,
+    correlationId: data.waitId,
+    eventData: { resumeAt: data.resumeAt },
+  });
+  if (!result.wait) {
+    throw new Error('Expected wait to be created');
+  }
+  return result.wait;
+}
+
+/**
+ * Complete a wait through the wait_completed event.
+ */
+export async function completeWait(
+  storage: Storage,
+  runId: string,
+  waitId: string
+): Promise<Wait> {
+  const result = await storage.events.create(runId, {
+    eventType: 'wait_completed',
+    specVersion: SPEC_VERSION_CURRENT,
+    correlationId: waitId,
+  });
+  if (!result.wait) {
+    throw new Error('Expected wait to be completed');
+  }
+  return result.wait;
+}