diff --git a/src/lib/entitySubmissionHelpers.ts b/src/lib/entitySubmissionHelpers.ts
index f5890a96..d5d7021f 100644
--- a/src/lib/entitySubmissionHelpers.ts
+++ b/src/lib/entitySubmissionHelpers.ts
@@ -347,6 +347,29 @@ async function submitCompositeCreation(
     depends_on: null // Will be set by RPC based on refs
   });
 
+  // Pre-validation to catch issues early with actionable error messages
+  if (uploadedPrimary.type === 'park') {
+    if (!primaryData.name) throw new Error('Park name is required');
+    if (!primaryData.slug) throw new Error('Park slug is required');
+    if (!primaryData.park_type) throw new Error('Park type is required');
+    if (!primaryData.status) throw new Error('Park status is required');
+  } else if (uploadedPrimary.type === 'ride') {
+    if (!primaryData.name) throw new Error('Ride name is required');
+    if (!primaryData.slug) throw new Error('Ride slug is required');
+    if (!primaryData.status) throw new Error('Ride status is required');
+  }
+
+  // Validate dependencies
+  for (const dep of uploadedDependencies) {
+    if (dep.type === 'company') {
+      if (!dep.data.name) throw new Error(`${dep.companyType || 'Company'} name is required`);
+      if (!dep.data.slug) throw new Error(`${dep.companyType || 'Company'} slug is required`);
+      if (!dep.data.company_type && !dep.companyType) {
+        throw new Error('Company type is required');
+      }
+    }
+  }
+
   // Use RPC to create submission with items atomically
   const { data: result, error } = await supabase.rpc('create_submission_with_items', {
     p_user_id: userId,
@@ -356,11 +379,30 @@ async function submitCompositeCreation(
   });
 
   if (error) {
-    handleError(error, {
+    // Extract Supabase error details for better error logging
+    const supabaseError = error as { message?: string; code?: string; details?: string; hint?: string };
+    const errorMessage = supabaseError.message || 'Unknown error';
+    const errorCode = supabaseError.code;
+    const errorDetails = supabaseError.details;
+    const errorHint = supabaseError.hint;
+    
+    // Create proper Error instance with enhanced context
+    const enhancedError = new Error(
+      `Composite submission failed: ${errorMessage}${errorDetails ? `\nDetails: ${errorDetails}` : ''}${errorHint ? `\nHint: ${errorHint}` : ''}`
+    );
+    
+    handleError(enhancedError, {
       action: 'Composite submission',
-      metadata: { primaryType: uploadedPrimary.type, dependencyCount: dependencies.length },
+      metadata: { 
+        primaryType: uploadedPrimary.type, 
+        dependencyCount: dependencies.length,
+        supabaseCode: errorCode,
+        supabaseDetails: errorDetails,
+        supabaseHint: errorHint
+      },
     });
-    throw new Error(`Failed to create composite submission: ${error instanceof Error ? error.message : 'Unknown error'}`);
+    
+    throw enhancedError;
   }
 
   return { submitted: true, submissionId: result };
diff --git a/src/lib/errorHandler.ts b/src/lib/errorHandler.ts
index 87a9f250..923e58cd 100644
--- a/src/lib/errorHandler.ts
+++ b/src/lib/errorHandler.ts
@@ -30,23 +30,60 @@ export const handleError = (
   const errorId = (context.metadata?.requestId as string) || crypto.randomUUID();
   const shortErrorId = errorId.slice(0, 8);
   
-  const errorMessage = error instanceof AppError 
-    ? error.userMessage || error.message
-    : error instanceof Error 
-    ? error.message 
-    : 'An unexpected error occurred';
+  // Enhanced error message and stack extraction
+  let errorMessage: string;
+  let stack: string | undefined;
+  let errorName = 'UnknownError';
+  
+  if (error instanceof Error) {
+    errorMessage = error instanceof AppError 
+      ? error.userMessage || error.message 
+      : error.message;
+    stack = error.stack;
+    errorName = error.name;
+  } else if (error && typeof error === 'object') {
+    // Handle Supabase errors (plain objects with message/code/details)
+    const supabaseError = error as { 
+      message?: string; 
+      code?: string; 
+      details?: string; 
+      hint?: string;
+    };
+    
+    errorMessage = supabaseError.message || 'An unexpected error occurred';
+    errorName = 'SupabaseError';
+    
+    // Create synthetic stack trace for Supabase errors to aid debugging
+    if (supabaseError.code || supabaseError.details || supabaseError.hint) {
+      const stackParts = [
+        `SupabaseError: ${errorMessage}`,
+        supabaseError.code ? `  Code: ${supabaseError.code}` : null,
+        supabaseError.details ? `  Details: ${supabaseError.details}` : null,
+        supabaseError.hint ? `  Hint: ${supabaseError.hint}` : null,
+        `  at ${context.action}`,
+        `  Reference ID: ${errorId}`
+      ].filter(Boolean);
+      
+      stack = stackParts.join('\n');
+    }
+  } else if (typeof error === 'string') {
+    errorMessage = error;
+  } else {
+    errorMessage = 'An unexpected error occurred';
+  }
 
   // Log to console/monitoring with enhanced debugging
-  const stack = error instanceof Error ? error.stack : undefined;
   
   logger.error('Error occurred', {
     ...context,
-    error: error instanceof Error ? error.message : String(error),
+    error: errorMessage,
     stack,
     errorId,
+    errorName,
     errorType: typeof error,
     errorConstructor: error?.constructor?.name,
     hasStack: !!stack,
+    isSyntheticStack: !!(error && typeof error === 'object' && !(error instanceof Error) && stack),
   });
   
   // Additional debug logging when stack is missing
@@ -72,9 +109,9 @@ export const handleError = (
       p_endpoint: context.action,
       p_method: 'ERROR',
       p_status_code: 500,
-      p_error_type: error instanceof Error ? error.name : 'UnknownError',
+      p_error_type: errorName,
       p_error_message: errorMessage,
-      p_error_stack: error instanceof Error ? error.stack : undefined,
+      p_error_stack: stack,
       p_user_agent: navigator.userAgent,
       p_breadcrumbs: JSON.stringify(breadcrumbs),
       p_timezone: envContext.timezone,