feat: check for duplicate phone number in campaign

api/services/campaign/source_validator.py

@@ -85,6 +85,36 @@ def _validate_source_data(
             ),
         )
 
+    # Check for duplicate phone numbers
+    seen_phones: dict[str, int] = {}  # phone -> first row where it appeared
+    duplicate_rows = []
+    for row_idx, row in enumerate(rows, start=2):
+        if len(row) <= phone_number_idx:
+            continue
+
+        phone_number = row[phone_number_idx].strip()
+        if not phone_number:
+            continue
+
+        if phone_number in seen_phones:
+            duplicate_rows.append(row_idx)
+        else:
+            seen_phones[phone_number] = row_idx
+
+    if duplicate_rows:
+        if len(duplicate_rows) > 5:
+            rows_str = f"{', '.join(map(str, duplicate_rows[:5]))} and {len(duplicate_rows) - 5} more"
+        else:
+            rows_str = ", ".join(map(str, duplicate_rows))
+
+        return ValidationResult(
+            is_valid=False,
+            error=ValidationError(
+                message=f"Duplicate phone numbers found in rows: {rows_str}. Phone numbers in a campaign must be unique.",
+                invalid_rows=duplicate_rows,
+            ),
+        )
+
     return ValidationResult(is_valid=True)