diff --git a/src/embed/search.spec.ts b/src/embed/search.spec.ts
index 6a953923..f855cd0f 100644
--- a/src/embed/search.spec.ts
+++ b/src/embed/search.spec.ts
@@ -77,6 +77,37 @@ describe('Search embed tests', () => {
         });
     });
 
+    test('getUpdateEmbedParamsObject sends dataSources as a real ARRAY, not the URL-encoded string', async () => {
+        // The iframe URL correctly carries dataSources as a JSON-encoded
+        // string (asserted above), but the UpdateEmbedParams postMessage
+        // payload is spread into app state unparsed — a string there reaches
+        // the $sources GraphQL variable ([GUID!]) and fails GUID coercion
+        // (SCAL-334713, fired from beforePrerenderVisible on prerender-show).
+        const dataSources = ['4dd30af7-9ed7-4847-8f28-b65b44a841d8'];
+        const searchEmbed = new SearchEmbed(getRootEl(), {
+            ...defaultViewConfig,
+            dataSources,
+        });
+        const params = await (searchEmbed as any).getUpdateEmbedParamsObject();
+        expect(params.dataSources).toEqual(dataSources);
+
+        // Single-GUID `dataSource` prop (the customer's shape) normalizes to
+        // a one-element array the same way the app's URL parser would.
+        const singleSourceEmbed = new SearchEmbed(getRootEl(), {
+            ...defaultViewConfig,
+            dataSource: '4dd30af7-9ed7-4847-8f28-b65b44a841d8',
+        });
+        const singleParams = await (singleSourceEmbed as any).getUpdateEmbedParamsObject();
+        expect(singleParams.dataSources).toEqual([
+            '4dd30af7-9ed7-4847-8f28-b65b44a841d8',
+        ]);
+
+        // The normalization only reverses JSON serialization: non-JSON
+        // strings and already-structured values pass through untouched.
+        expect(singleParams.embedApp).toBe(true);
+        expect(singleParams.authType).toBe('None');
+    });
+
     test('should pass in search query', async () => {
         const dataSources = ['data-source-1'];
         const searchOptions = {
diff --git a/src/embed/ts-embed.ts b/src/embed/ts-embed.ts
index 10ed5d53..b835eb86 100644
--- a/src/embed/ts-embed.ts
+++ b/src/embed/ts-embed.ts
@@ -38,6 +38,7 @@ import {
     isUndefined,
     getHostEventsConfig,
     getValueFromWindow,
+    deserializeParam,
 } from '../utils';
 import { getCustomActions } from '../utils/custom-actions';
 import {
@@ -706,11 +707,14 @@ export class TsEmbed {
     }
 
     protected async getUpdateEmbedParamsObject() {
-        let queryParams = this.getEmbedParamsObject();
+        const queryParams = this.getEmbedParamsObject();
+        // Values are URL-serialized (e.g. dataSources as '["guid"]'); parse
+        // them back so the event payload matches a URL load (SCAL-334713).
+        Object.keys(queryParams).forEach((key) => {
+            queryParams[key] = deserializeParam(queryParams[key]);
+        });
         const appInitData = await this.getAppInitData();
-        queryParams = { ...this.viewConfig, ...queryParams, ...appInitData };
-
-        return queryParams;
+        return { ...this.viewConfig, ...queryParams, ...appInitData };
     }
 
     /**
diff --git a/src/utils.spec.ts b/src/utils.spec.ts
index 65dc0459..e01c1364 100644
--- a/src/utils.spec.ts
+++ b/src/utils.spec.ts
@@ -1,5 +1,6 @@
 import {
     getQueryParamString,
+    deserializeParam,
     getFilterQuery,
     getCssDimension,
     getEncodedQueryParamsString,
@@ -348,7 +349,50 @@ describe('unit test for utils', () => {
     });
 });
 
+describe('deserializeParam', () => {
+    // Inverse of URL param serialization — must mirror the app's URL parser.
+    test('parses a JSON-string array back to a real array (SCAL-334713)', () => {
+        expect(deserializeParam('["4dd30af7-9ed7-4847-8f28-b65b44a841d8"]')).toEqual([
+            '4dd30af7-9ed7-4847-8f28-b65b44a841d8',
+        ]);
+    });
+
+    test('does not URI-decode strings — raw %xx content must survive', () => {
+        expect(deserializeParam('%5Bcommit%20date%5D%5Brevenue%5D')).toBe(
+            '%5Bcommit%20date%5D%5Brevenue%5D',
+        );
+    });
+
+    test('parses JSON objects and booleans', () => {
+        expect(deserializeParam('{"a":1}')).toEqual({ a: 1 });
+        expect(deserializeParam('true')).toBe(true);
+    });
+
+    test('keeps numeric strings as strings, matching the app URL parser', () => {
+        expect(deserializeParam('123')).toBe('123');
+        expect(deserializeParam('1.5')).toBe('1.5');
+    });
+
+    test('keeps plain non-JSON strings unchanged', () => {
+        expect(deserializeParam('local-host')).toBe('local-host');
+        expect(deserializeParam('AuthServerCookieless')).toBe('AuthServerCookieless');
+    });
+
+    test('keeps a malformed percent-sequence string as-is', () => {
+        expect(deserializeParam('100% legit')).toBe('100% legit');
+    });
+
+    test('passes non-string values through untouched', () => {
+        const arr = ['a'];
+        expect(deserializeParam(arr)).toBe(arr);
+        expect(deserializeParam(true)).toBe(true);
+        expect(deserializeParam(42)).toBe(42);
+        expect(deserializeParam(undefined)).toBeUndefined();
+    });
+});
+
 describe('Fullscreen Utility Functions', () => {
+
     let originalExitFullscreen: any;
     let mockIframe: HTMLIFrameElement;
 
diff --git a/src/utils.ts b/src/utils.ts
index 33786a2f..bcdb6a06 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -85,6 +85,22 @@ const serializeParam = (value: any) => {
     return JSON.stringify(value);
 };
 
+/**
+ * Inverse of serializeParam: JSON.parse with fallback to the raw string,
+ * matching how the app parses the same values from the iframe URL.
+ */
+export const deserializeParam = (value: unknown): unknown => {
+    if (typeof value !== 'string') return value;
+    try {
+        const parsed = JSON.parse(value);
+        // Numeric strings stay strings ('123' !== 123), same as the app's
+        // URL parser — param consumers expect string ids/versions.
+        return typeof parsed === 'number' ? value : parsed;
+    } catch (e) {
+        return value;
+    }
+};
+
 /**
  * Convert a value to a string:
  * in case of an array, we convert it to CSV.