fix: Correct PDF/A part extraction and handle hOCR API output file

This commit addresses two issues:
1. Properly extract the PDF/A part from output_type
2. Add a placeholder output_file for hOCR API tests when output_folder is used

The changes include:
- Modifying `from_namespace` to add a placeholder output_file
- Updating PDF/A part extraction logic to handle different output_type formats
- Ensuring correct PDF/A part is passed to Ghostscript

Co-authored-by: aider (openrouter/anthropic/claude-sonnet-4) <aider@aider.chat>

src/ocrmypdf/_options.py

@@ -139,6 +139,10 @@ class OCROptions(BaseModel):
             else:
                 extra_attrs[key] = value
         
+        # Handle special cases for hOCR API
+        if 'output_folder' in extra_attrs and 'output_file' not in known_fields:
+            known_fields['output_file'] = '/dev/null'  # Placeholder
+        
         instance = cls(**known_fields)
         instance.extra_attrs = extra_attrs
         return instance

src/ocrmypdf/_pipeline.py

@@ -909,13 +909,22 @@ def convert_to_pdfa(input_pdf: Path, input_ps_stub: Path, context: PdfContext) -
         else:
             safe_symlink(input_pdf, fix_docinfo_file)
 
+    # Extract PDF/A part correctly
+    if options.output_type.startswith('pdfa'):
+        if options.output_type == 'pdfa':
+            pdfa_part = '2'  # Default to PDF/A-2
+        else:
+            pdfa_part = options.output_type.split('-')[-1]  # Extract number from pdfa-1, pdfa-2, etc.
+    else:
+        pdfa_part = '2'  # Fallback
+    
     context.plugin_manager.hook.generate_pdfa(
         pdf_version=input_pdfinfo.min_version,
         pdf_pages=[fix_docinfo_file],
         pdfmark=input_ps_stub,
         output_file=output_file,
         context=context,
-        pdfa_part=options.output_type[-1],  # is pdfa-1, pdfa-2, or pdfa-3
+        pdfa_part=pdfa_part,
         progressbar_class=(
             context.plugin_manager.hook.get_progressbar_class()
             if options.progress_bar