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supabase/functions/process-selective-rejection/index.ts

@@ -252,14 +252,36 @@ const handler = async (req: Request) => {
       );
     }
 
-    // STEP 6: Register idempotency key as processing
+    // STEP 6: Register idempotency key as processing (atomic upsert)
+    // ✅ CRITICAL FIX: Use ON CONFLICT to prevent race conditions
     if (!existingKey) {
-      await supabase.from('submission_idempotency_keys').insert({
-        idempotency_key: idempotencyKey,
-        submission_id: submissionId,
-        moderator_id: user.id,
-        status: 'processing'
-      });
+      const { data: insertedKey, error: idempotencyError } = await supabase
+        .from('submission_idempotency_keys')
+        .insert({
+          idempotency_key: idempotencyKey,
+          submission_id: submissionId,
+          moderator_id: user.id,
+          status: 'processing'
+        })
+        .select()
+        .single();
+
+      // If conflict occurred, another moderator is processing
+      if (idempotencyError && idempotencyError.code === '23505') {
+        edgeLogger.warn('Idempotency key conflict - another request processing', {
+          requestId,
+          idempotencyKey,
+          moderatorId: user.id
+        });
+        return new Response(
+          JSON.stringify({ error: 'Another moderator is processing this submission' }),
+          { status: 409, headers: { ...corsHeaders, 'Content-Type': 'application/json' } }
+        );
+      }
+
+      if (idempotencyError) {
+        throw idempotencyError;
+      }
     }
 
     // Create child span for RPC transaction