fix(validators): validate regex patterns at init time

ContainsValidator and ExcludesValidator now pre-compile regex patterns
during initialisation and raise InvalidThresholdError if invalid.

src/veritext/validators/constraint.py

@@ -229,7 +229,7 @@ class ContainsValidator:
             case_sensitive: Whether matching is case-sensitive. Defaults to False.
 
         Raises:
-            InvalidThresholdError: If patterns list is empty.
+            InvalidThresholdError: If patterns list is empty or contains invalid regex.
         """
         if not patterns:
             raise InvalidThresholdError("patterns list cannot be empty")
@@ -238,6 +238,15 @@ class ContainsValidator:
         self._case_sensitive = case_sensitive
         self._flags = 0 if case_sensitive else re.IGNORECASE
 
+        self._compiled_patterns: list[re.Pattern[str]] = []
+        for pattern in patterns:
+            try:
+                self._compiled_patterns.append(re.compile(pattern, self._flags))
+            except re.error as e:
+                raise InvalidThresholdError(
+                    f"Invalid regex pattern '{pattern}': {e}"
+                ) from e
+
     @property
     def name(self) -> str:
         """Return the name of this check."""
@@ -255,8 +264,10 @@ class ContainsValidator:
             CheckResult with pass/fail status.
         """
         missing = []
-        for pattern in self._patterns:
+        for pattern, compiled in zip(
-            if not re.search(pattern, text, self._flags):
+            self._patterns, self._compiled_patterns, strict=True
+        ):
+            if not compiled.search(text):
                 missing.append(pattern)
 
         passed = len(missing) == 0
@@ -291,7 +302,7 @@ class ExcludesValidator:
             case_sensitive: Whether matching is case-sensitive. Defaults to False.
 
         Raises:
-            InvalidThresholdError: If patterns list is empty.
+            InvalidThresholdError: If patterns list is empty or contains invalid regex.
         """
         if not patterns:
             raise InvalidThresholdError("patterns list cannot be empty")
@@ -300,6 +311,15 @@ class ExcludesValidator:
         self._case_sensitive = case_sensitive
         self._flags = 0 if case_sensitive else re.IGNORECASE
 
+        self._compiled_patterns: list[re.Pattern[str]] = []
+        for pattern in patterns:
+            try:
+                self._compiled_patterns.append(re.compile(pattern, self._flags))
+            except re.error as e:
+                raise InvalidThresholdError(
+                    f"Invalid regex pattern '{pattern}': {e}"
+                ) from e
+
     @property
     def name(self) -> str:
         """Return the name of this check."""
@@ -317,8 +337,10 @@ class ExcludesValidator:
             CheckResult with pass/fail status.
         """
         found = []
-        for pattern in self._patterns:
+        for pattern, compiled in zip(
-            if re.search(pattern, text, self._flags):
+            self._patterns, self._compiled_patterns, strict=True
+        ):
+            if compiled.search(text):
                 found.append(pattern)
 
         passed = len(found) == 0

tests/test_validators/test_constraint.py

@@ -263,6 +263,11 @@ class TestContainsValidator:
         with pytest.raises(InvalidThresholdError, match="cannot be empty"):
             ContainsValidator(patterns=[])
 
+    def test_contains_validator_raises_on_invalid_regex(self) -> None:
+        """Test that invalid regex pattern raises error at init time."""
+        with pytest.raises(InvalidThresholdError, match="Invalid regex"):
+            ContainsValidator(patterns=[r"[invalid"])
+
     def test_contains_factory_function(self) -> None:
         """Test the contains() factory function."""
         validator = contains(patterns=["test"], case_sensitive=True)
@@ -327,6 +332,11 @@ class TestExcludesValidator:
         with pytest.raises(InvalidThresholdError, match="cannot be empty"):
             ExcludesValidator(patterns=[])
 
+    def test_excludes_validator_raises_on_invalid_regex(self) -> None:
+        """Test that invalid regex pattern raises error at init time."""
+        with pytest.raises(InvalidThresholdError, match="Invalid regex"):
+            ExcludesValidator(patterns=[r"[invalid"])
+
     def test_excludes_factory_function(self) -> None:
         """Test the excludes() factory function."""
         validator = excludes(patterns=["test"], case_sensitive=True)