diff --git a/frontend/src/hooks/useReasoningTranslation.ts b/frontend/src/hooks/useReasoningTranslation.ts
index df9431df..5673e25c 100644
--- a/frontend/src/hooks/useReasoningTranslation.ts
+++ b/frontend/src/hooks/useReasoningTranslation.ts
@@ -29,15 +29,17 @@ export function useReasoningTranslation() {
 
   /**
    * Translate purchase order reasoning
+   * IMPORTANT: Always returns a string, never undefined
    */
   const translatePOReasonng = (reasoningData: ReasoningData): string => {
     if (!reasoningData || !reasoningData.type) {
-      return t('purchaseOrder.low_stock_detection', {
+      const fallback = t('purchaseOrder.low_stock_detection', {
         supplier_name: 'Unknown',
         product_names_joined: 'Items',
         days_until_stockout: 7,
         defaultValue: 'Purchase order required for inventory replenishment'
       });
+      return String(fallback || 'Purchase order required');
     }
 
     const { type, parameters } = reasoningData;
@@ -51,21 +53,24 @@ export function useReasoningTranslation() {
       defaultValue: `Purchase order: ${type}`
     };
 
-    return t(`purchaseOrder.${type}`, params) || `Purchase order: ${type}`;
+    const result = t(`purchaseOrder.${type}`, params);
+    return String(result || `Purchase order: ${type}`);
   };
 
   /**
    * Translate production batch reasoning
+   * IMPORTANT: Always returns a string, never undefined
    */
   const translateBatchReasoning = (reasoningData: ReasoningData): string => {
     if (!reasoningData || !reasoningData.type) {
-      return t('productionBatch.forecast_demand', {
+      const fallback = t('productionBatch.forecast_demand', {
         product_name: 'Product',
         predicted_demand: 0,
         current_stock: 0,
         confidence_score: 85,
         defaultValue: 'Production batch scheduled based on demand forecast'
       });
+      return String(fallback || 'Production batch scheduled');
     }
 
     const { type, parameters } = reasoningData;
@@ -73,11 +78,13 @@ export function useReasoningTranslation() {
       ...parameters,
       defaultValue: `Production batch: ${type}`
     };
-    return t(`productionBatch.${type}`, params) || `Production batch: ${type}`;
+    const result = t(`productionBatch.${type}`, params);
+    return String(result || `Production batch: ${type}`);
   };
 
   /**
    * Translate consequence text
+   * IMPORTANT: Always returns a string, never undefined
    */
   const translateConsequence = (consequenceData?: any): string => {
     if (!consequenceData || !consequenceData.type) {
@@ -92,30 +99,37 @@ export function useReasoningTranslation() {
       defaultValue: `Impact: ${consequenceData.type}`
     };
 
-    return t(`consequence.${consequenceData.type}`, params) || '';
+    const result = t(`consequence.${consequenceData.type}`, params);
+    return String(result || '');
   };
 
   /**
    * Translate severity level
+   * IMPORTANT: Always returns a string, never undefined
    */
   const translateSeverity = (severity?: string): string => {
     if (!severity) return '';
-    return t(`severity.${severity}`, { defaultValue: severity }) || '';
+    const result = t(`severity.${severity}`, { defaultValue: severity });
+    return String(result || '');
   };
 
   /**
    * Translate trigger source
+   * IMPORTANT: Always returns a string, never undefined
    */
   const translateTrigger = (trigger?: string): string => {
     if (!trigger) return '';
-    return t(`triggers.${trigger}`, { defaultValue: trigger }) || '';
+    const result = t(`triggers.${trigger}`, { defaultValue: trigger });
+    return String(result || '');
   };
 
   /**
    * Translate error code
+   * IMPORTANT: Always returns a string, never undefined
    */
   const translateError = (errorCode: string): string => {
-    return t(`errors.${errorCode}`, { defaultValue: errorCode });
+    const result = t(`errors.${errorCode}`, { defaultValue: errorCode });
+    return String(result || errorCode);
   };
 
   return {
@@ -141,17 +155,17 @@ export function useReasoningFormatter() {
 
     if (!reasoningData) {
       const fallback = {
-        reasoning: translation.translatePOReasonng({} as ReasoningData) || 'Purchase order required',
-        consequence: '',
-        severity: ''
+        reasoning: String(translation.translatePOReasonng({} as ReasoningData) || 'Purchase order required'),
+        consequence: String(''),
+        severity: String('')
       };
       console.log('🔍 formatPOAction: No reasoning data, returning fallback:', fallback);
       return fallback;
     }
 
-    const reasoning = translation.translatePOReasonng(reasoningData) || 'Purchase order required';
-    const consequence = translation.translateConsequence(reasoningData.consequence) || '';
-    const severity = translation.translateSeverity(reasoningData.consequence?.severity) || '';
+    const reasoning = String(translation.translatePOReasonng(reasoningData) || 'Purchase order required');
+    const consequence = String(translation.translateConsequence(reasoningData.consequence) || '');
+    const severity = String(translation.translateSeverity(reasoningData.consequence?.severity) || '');
 
     const result = { reasoning, consequence, severity };
 
@@ -176,15 +190,15 @@ export function useReasoningFormatter() {
 
     if (!reasoningData) {
       const fallback = {
-        reasoning: translation.translateBatchReasoning({} as ReasoningData) || 'Production batch scheduled',
-        urgency: 'normal'
+        reasoning: String(translation.translateBatchReasoning({} as ReasoningData) || 'Production batch scheduled'),
+        urgency: String('normal')
       };
       console.log('🔍 formatBatchAction: No reasoning data, returning fallback:', fallback);
       return fallback;
     }
 
-    const reasoning = translation.translateBatchReasoning(reasoningData) || 'Production batch scheduled';
-    const urgency = reasoningData.urgency?.level || 'normal';
+    const reasoning = String(translation.translateBatchReasoning(reasoningData) || 'Production batch scheduled');
+    const urgency = String(reasoningData.urgency?.level || 'normal');
 
     const result = { reasoning, urgency };