fix: improve error handling in background expense processing

- Add proper array validation for existingExpenses API response
- Handle different API response structures (data.expenses vs data)
- Add try-catch blocks around individual expense processing loops
- Improve error messages to show specific error details
- Prevent TypeError when API response format is unexpected

Resolves 'gt.some is not a function' error in background processing.

client/src/pages/DataImport.tsx

@@ -79,7 +79,15 @@ export default function DataImport() {
     try {
       setBackgroundProcessing('Processing expenses from uploaded files...');
       
-      const existingExpenses = await api.get('/expenses').then(res => res.data);
+      const existingExpensesResponse = await api.get('/expenses');
+      const existingExpenses = existingExpensesResponse.data?.expenses || existingExpensesResponse.data || [];
+      
+      // Ensure existingExpenses is an array
+      if (!Array.isArray(existingExpenses)) {
+        console.warn('Expected existingExpenses to be an array, got:', typeof existingExpenses, existingExpenses);
+        throw new Error('Invalid response format for existing expenses');
+      }
+      
       const expensesToCreate: any[] = [];
 
       if (etsyFile) {
@@ -88,6 +96,7 @@ export default function DataImport() {
         
         // Add Etsy fees (check for duplicates)
         etsyFees.forEach((fee: EtsyFeeRecord) => {
+          try {
             const isDuplicate = existingExpenses.some((expense: any) => 
               expense.description === fee.description && 
               Math.abs(expense.amount - fee.amount) < 0.01 && 
@@ -106,6 +115,9 @@ export default function DataImport() {
                 reference: fee.reference
               });
             }
+          } catch (error) {
+            console.error('Error processing Etsy fee:', fee, error);
+          }
         });
       }
 
@@ -115,6 +127,7 @@ export default function DataImport() {
         
         // Add shipping expenses (check for duplicates)
         shippingRecords.forEach((shipping: ParsedShippingRecord) => {
+          try {
             if (shipping.totalCost > 0) {
               const isDuplicate = existingExpenses.some((expense: any) => 
                 expense.reference === shipping.trackingNumber && 
@@ -135,6 +148,9 @@ export default function DataImport() {
                 });
               }
             }
+          } catch (error) {
+            console.error('Error processing shipping record:', shipping, error);
+          }
         });
       }
 
@@ -169,7 +185,11 @@ export default function DataImport() {
       }
     } catch (error) {
       console.error('Error in background expense processing:', error);
+      if (error instanceof Error) {
+        toast.error(`Error processing expenses: ${error.message}`);
+      } else {
         toast.error('Error processing expenses in background');
+      }
     } finally {
       setBackgroundProcessing('');
     }