Update app.py

app.py

@@ -1847,7 +1847,10 @@ def rewrite_residual_list_comma(sent, coordinator="and"):
     """
     Last list-separator comma → same conjunction as the split sign,
     so the next pass sees CMN1/CMV1/CCV more reliably (not SSMN).
-    Skips comma before a bare number (e.g. Smith, 43).
+    Skips:
+      - comma before a bare number (Smith, 43)
+      - a comma that already introduces a coordinator
+        (", and" / ", or" / ", but") — copying would produce "and and"
     """
     if not sent or not coordinator:
         return sent
@@ -1856,12 +1859,21 @@ def rewrite_residual_list_comma(sent, coordinator="and"):
         return sent
 
     s = sent.strip()
+
+    # already a well-formed list: ", and X" must be left alone
+    if re.search(r",\s+(?:and|or|but)\b", s, flags=re.I):
+        return s
+
     m = re.search(r",\s+(?!\d\b)([^,]+?)(\s*[.!?])?\s*$", s)
     if not m:
         return s
 
-    head = s[: m.start()].rstrip()
     tail = m.group(1).strip()
+    # tail itself starts with a coordinator — do not double it
+    if re.match(r"(?:and|or|but)\b", tail, flags=re.I):
+        return s
+
+    head = s[: m.start()].rstrip()
     punct = (m.group(2) or "").strip() or "."
     out = f"{head} {coord} {tail}{punct}"
     out = re.sub(r"\s+", " ", out).strip()