Normalize unpaper_args to list at construction time

Use a Pydantic field validator to convert string input to list[str]
during OcrOptions construction, simplifying the type from
`str | list[str] | None` to `list[str] | None`. Security validation
(path injection check) now happens at construction rather than in
check_options_preprocessing().

src/ocrmypdf/_exec/unpaper.py

@@ -7,7 +7,6 @@ from __future__ import annotations
 
 import logging
 import os
-import shlex
 from collections.abc import Iterator
 from contextlib import contextmanager
 from decimal import Decimal
@@ -101,13 +100,6 @@ def run_unpaper(
             ) from e
 
 
-def validate_custom_args(args: str) -> list[str]:
-    unpaper_args = shlex.split(args)
-    if any(('/' in arg or arg == '.' or arg == '..') for arg in unpaper_args):
-        raise ValueError('No filenames allowed in --unpaper-args')
-    return unpaper_args
-
-
 def clean(
     input_file: Path,
     output_file: Path,

src/ocrmypdf/_options.py

@@ -8,6 +8,7 @@ from __future__ import annotations
 import json
 import logging
 import os
+import shlex
 import unicodedata
 from collections.abc import Sequence
 from enum import StrEnum
@@ -156,9 +157,7 @@ class OcrOptions(BaseModel):
     remove_background: bool = False
     remove_vectors: bool = False
     oversample: int = 0
-    unpaper_args: str | list[str] | None = (
-        None  # Can be string or list after validation
-    )
+    unpaper_args: list[str] | None = None
 
     # OCR behavior
     skip_big: float | None = None
@@ -339,6 +338,20 @@ class OcrOptions(BaseModel):
         # Convert string ranges to set of page numbers
         return _pages_from_ranges(v)
 
+    @field_validator('unpaper_args', mode='before')
+    @classmethod
+    def validate_unpaper_args(cls, v):
+        """Normalize unpaper_args from string to list and validate security."""
+        if v is None:
+            return v
+        if isinstance(v, str):
+            v = shlex.split(v)
+        if isinstance(v, list):
+            if any(('/' in arg or arg == '.' or arg == '..') for arg in v):
+                raise ValueError('No filenames allowed in --unpaper-args')
+            return v
+        raise ValueError(f'unpaper_args must be a string or list, got {type(v)}')
+
     @model_validator(mode='before')
     @classmethod
     def handle_special_cases(cls, data):

src/ocrmypdf/_validation.py

@@ -114,15 +114,8 @@ def check_options_preprocessing(options: OcrOptions) -> None:
             package='unpaper',
             version_checker=unpaper.version,
             need_version='6.1',
-            required_for="--clean, --clean-final",  # Problem arguments
+            required_for="--clean, --clean-final",
         )
-        try:
-            if options.unpaper_args:
-                options.unpaper_args = unpaper.validate_custom_args(
-                    options.unpaper_args
-                )
-        except Exception as e:
-            raise BadArgsError("--unpaper-args: " + str(e)) from e
 
 
 def _check_plugin_invariant_options(options: OcrOptions) -> None:

tests/test_unpaper.py

@@ -9,11 +9,12 @@ from unittest.mock import Mock, patch
 
 import pytest
 from packaging.version import Version
+from pydantic import ValidationError
 
 from ocrmypdf._exec import unpaper
 from ocrmypdf._validation import check_options
 from ocrmypdf.cli import get_options_and_plugins
-from ocrmypdf.exceptions import BadArgsError, ExitCode, MissingDependencyError
+from ocrmypdf.exceptions import ExitCode, MissingDependencyError
 
 from .conftest import check_ocrmypdf, have_unpaper, run_ocrmypdf_api
 
@@ -87,7 +88,7 @@ def test_unpaper_args_valid(resources, outpdf):
 
 @needs_unpaper
 def test_unpaper_args_invalid_filename(resources, outpdf, caplog):
-    with pytest.raises(BadArgsError):
+    with pytest.raises(ValidationError, match="No filenames allowed"):
         run_ocrmypdf_api(
             resources / "skew.pdf",
             outpdf,