fix: suffixes_prefixes_titles always reflects current set state

The `suffixes_prefixes_titles` property on `Constants` cached its result
in `_pst` after the first access.  Any subsequent `add()` or `remove()`
call on `titles`, `prefixes`, `suffix_acronyms`, or `suffix_not_acronyms`
was silently ignored by the cache, so `is_rootname()` kept returning the
stale result.

Concretely, a word added to `C.titles` after the property was first
accessed would still be treated as a rootname (first/middle/last) by
`join_on_conjunctions`, even though `is_title()` correctly returned
`True` for it.  This contradicts the documented behaviour of per-instance
config customisation described in AGENTS.md.

Fix: drop the `_pst` cache entirely and compute the union fresh on every
access.  The four-set union is cheap and the simplest correct approach.

Add five tests that assert the property and `is_rootname` stay consistent
with the live sets after `add()`/`remove()` calls.

Author: binggao1230

nameparser/config/__init__.py

@@ -179,7 +179,6 @@ class Constants:
     capitalization_exceptions: TupleManager[str]
     regexes: RegexTupleManager
 
-    _pst: Set[str] | None
 
     string_format = "{title} {first} {middle} {last} {suffix} ({nickname})"
     """
@@ -262,13 +261,10 @@ def __init__(self,
         self.conjunctions = SetManager(conjunctions)
         self.capitalization_exceptions = TupleManager(capitalization_exceptions)
         self.regexes = RegexTupleManager(regexes)
-        self._pst = None
 
     @property
     def suffixes_prefixes_titles(self) -> Set[str]:
-        if not self._pst:
-            self._pst = self.prefixes | self.suffix_acronyms | self.suffix_not_acronyms | self.titles
-        return self._pst
+        return self.prefixes | self.suffix_acronyms | self.suffix_not_acronyms | self.titles
 
     def __repr__(self) -> str:
         return "<Constants() instance>"

tests/test_constants.py

@@ -104,3 +104,35 @@ def test_add_constant_with_explicit_encoding(self) -> None:
         c = Constants()
         c.titles.add_with_encoding(b'b\351ck', encoding='latin_1')
         self.assertIn('béck', c.titles)
+
+    def test_suffixes_prefixes_titles_reflects_add_title(self) -> None:
+        """suffixes_prefixes_titles must include titles added after construction."""
+        c = Constants()
+        c.titles.add('emerita')
+        self.assertIn('emerita', c.suffixes_prefixes_titles)
+
+    def test_suffixes_prefixes_titles_reflects_add_prefix(self) -> None:
+        """suffixes_prefixes_titles must include prefixes added after construction."""
+        c = Constants()
+        c.prefixes.add('xpfx')
+        self.assertIn('xpfx', c.suffixes_prefixes_titles)
+
+    def test_suffixes_prefixes_titles_reflects_remove_title(self) -> None:
+        """suffixes_prefixes_titles must not include a word that was only in titles and is then removed."""
+        c = Constants()
+        c.titles.add('emerita')
+        self.assertIn('emerita', c.suffixes_prefixes_titles)
+        c.titles.remove('emerita')
+        self.assertFalse('emerita' in c.suffixes_prefixes_titles)
+
+    def test_is_rootname_consistent_with_is_title(self) -> None:
+        """is_rootname must return False for words recognised by is_title."""
+        hn = HumanName("", constants=None)
+        hn.C.titles.add('emerita')
+        self.assertFalse(hn.is_rootname('emerita'))
+
+    def test_is_rootname_consistent_with_is_prefix(self) -> None:
+        """is_rootname must return False for words recognised by is_prefix."""
+        hn = HumanName("", constants=None)
+        hn.C.prefixes.add('xpfx')
+        self.assertFalse(hn.is_rootname('xpfx'))