diff --git a/src/client.ts b/src/client.ts
index 8aa63f3..630b8cf 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -397,6 +397,7 @@ export function createClientFromRequest(request: Request): Base44Client {
   const serverUrlHeader = request.headers.get("Base44-Api-Url");
   const functionsVersion = request.headers.get("Base44-Functions-Version");
   const stateHeader = request.headers.get("Base44-State");
+  const dataEnvHeader = request.headers.get("X-Data-Env");
 
   if (!appId) {
     throw new Error(
@@ -439,6 +440,16 @@ export function createClientFromRequest(request: Request): Base44Client {
   if (stateHeader) {
     additionalHeaders["Base44-State"] = stateHeader;
   }
+  // Propagate the data environment so entity operations from the function stay
+  // in the same environment (e.g. test data) as the triggering request. This
+  // matters for the user-scoped client: unlike the service token, the user JWT
+  // carries no data-env, so without forwarding this header the callbacks fall
+  // back to production data even when the app runs in test-data mode.
+  // Forward only the known closed set (matches the backend contract) rather
+  // than relaying an arbitrary attacker-supplied header value onward.
+  if (dataEnvHeader === "dev" || dataEnvHeader === "prod") {
+    additionalHeaders["X-Data-Env"] = dataEnvHeader;
+  }
 
   return createClient({
     serverUrl: serverUrlHeader || "https://base44.app",
diff --git a/tests/unit/client.test.js b/tests/unit/client.test.js
index 4a7b3ef..5ba2eba 100644
--- a/tests/unit/client.test.js
+++ b/tests/unit/client.test.js
@@ -540,6 +540,88 @@ describe('Service Role Authorization Headers', () => {
     expect(scope.isDone()).toBe(true);
   });
 
+  test('should propagate X-Data-Env header on user-scoped API requests when created from request', async () => {
+    const mockRequest = {
+      headers: {
+        get: (name) => {
+          const headers = {
+            'Authorization': 'Bearer user-token-123',
+            'Base44-App-Id': appId,
+            'Base44-Api-Url': serverUrl,
+            'X-Data-Env': 'dev'
+          };
+          return headers[name] || null;
+        }
+      }
+    };
+
+    const client = createClientFromRequest(mockRequest);
+
+    // The user-scoped client (not asServiceRole) must still carry the data env
+    // so test-mode function callbacks hit test data, not production.
+    scope.get(`/api/apps/${appId}/entities/Todo`)
+      .matchHeader('X-Data-Env', 'dev')
+      .matchHeader('Authorization', 'Bearer user-token-123')
+      .reply(200, { items: [], total: 0 });
+
+    await client.entities.Todo.list();
+
+    expect(scope.isDone()).toBe(true);
+  });
+
+  test('should not forward an X-Data-Env value outside the dev/prod set', async () => {
+    const mockRequest = {
+      headers: {
+        get: (name) => {
+          const headers = {
+            'Authorization': 'Bearer user-token-123',
+            'Base44-App-Id': appId,
+            'Base44-Api-Url': serverUrl,
+            'X-Data-Env': 'evil'
+          };
+          return headers[name] || null;
+        }
+      }
+    };
+
+    const client = createClientFromRequest(mockRequest);
+
+    scope.get(`/api/apps/${appId}/entities/Todo`)
+      .matchHeader('X-Data-Env', (val) => !val) // arbitrary value must not be relayed
+      .matchHeader('Authorization', 'Bearer user-token-123')
+      .reply(200, { items: [], total: 0 });
+
+    await client.entities.Todo.list();
+
+    expect(scope.isDone()).toBe(true);
+  });
+
+  test('should not include X-Data-Env header when not present in original request', async () => {
+    const mockRequest = {
+      headers: {
+        get: (name) => {
+          const headers = {
+            'Authorization': 'Bearer user-token-123',
+            'Base44-App-Id': appId,
+            'Base44-Api-Url': serverUrl
+          };
+          return headers[name] || null;
+        }
+      }
+    };
+
+    const client = createClientFromRequest(mockRequest);
+
+    scope.get(`/api/apps/${appId}/entities/Todo`)
+      .matchHeader('X-Data-Env', (val) => !val) // Should not have this header
+      .matchHeader('Authorization', 'Bearer user-token-123')
+      .reply(200, { items: [], total: 0 });
+
+    await client.entities.Todo.list();
+
+    expect(scope.isDone()).toBe(true);
+  });
+
   test('should not include Base44-State header when not present in original request', async () => {
     const mockRequest = {
       headers: {