fix: Preflight-Check und Exit-Code in --once Modus (v0.2.1)

- #1: check_preflight() prüft beim Start tesseract + gs, wirft
  PreflightError. CLI endet mit Exit 2 statt grün zu bleiben.
- #2: run_once() gibt Anzahl fehlgeschlagener PDFs zurück, CLI
  endet mit Exit 1 wenn mindestens eine Datei scheiterte.
- pytest-Suite mit 11 Tests für beide Szenarien
- ocrmypdf-Import lazy in processor.py (Tests ohne ocrmypdf möglich)

Closes #1, #2

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_once_exit_code.py

@@ -0,0 +1,96 @@
+"""Tests für Issue #2: --once Modus muss Exit-Code != 0 bei Fehlern liefern."""
+from __future__ import annotations
+
+from pathlib import Path
+from unittest.mock import patch
+
+from pdf_ocr_hotfolder.processor import ProcessResult
+from pdf_ocr_hotfolder.service import HotfolderService
+
+
+def _fake_success(src: Path, working_dir, outgoing_dir, error_dir, ocr_cfg, vera_cfg):
+    out = outgoing_dir / f"OCR_{src.name}"
+    out.parent.mkdir(parents=True, exist_ok=True)
+    out.write_bytes(b"%PDF-1.4 ocr\n")
+    src.unlink(missing_ok=True)
+    return ProcessResult(src, out, True)
+
+
+def _fake_failure(src: Path, working_dir, outgoing_dir, error_dir, ocr_cfg, vera_cfg):
+    error_dir.mkdir(parents=True, exist_ok=True)
+    dest = error_dir / src.name
+    src.rename(dest)
+    return ProcessResult(src, outgoing_dir / f"OCR_{src.name}", False,
+                         error="fake ocr failure")
+
+
+def _run(tmp_config, fake_process):
+    """Helper: führt run_once() mit gemocktem process_pdf und preflight aus."""
+    with patch("pdf_ocr_hotfolder.service.check_preflight", return_value=None), \
+         patch("pdf_ocr_hotfolder.service.process_pdf", side_effect=fake_process), \
+         patch("pdf_ocr_hotfolder.service._wait_until_stable", return_value=True):
+        service = HotfolderService(tmp_config)
+        try:
+            return service.run_once()
+        finally:
+            service._executor.shutdown(wait=False)
+
+
+def test_once_exit_0_when_no_files(tmp_config) -> None:
+    """Szenario: Keine PDFs vorhanden → Exit 0."""
+    errors = _run(tmp_config, _fake_success)
+    assert errors == 0
+
+
+def test_once_exit_0_when_all_success(tmp_config) -> None:
+    """Szenario: Alle PDFs erfolgreich → Exit 0."""
+    (tmp_config.paths.incoming / "a.pdf").write_bytes(b"%PDF-1.4\n")
+    (tmp_config.paths.incoming / "b.pdf").write_bytes(b"%PDF-1.4\n")
+
+    errors = _run(tmp_config, _fake_success)
+    assert errors == 0
+
+
+def test_once_exit_nonzero_when_all_fail(tmp_config) -> None:
+    """Szenario: Alle PDFs fehlgeschlagen → Exit != 0 (Issue #2)."""
+    (tmp_config.paths.incoming / "a.pdf").write_bytes(b"%PDF-1.4\n")
+    (tmp_config.paths.incoming / "b.pdf").write_bytes(b"%PDF-1.4\n")
+
+    errors = _run(tmp_config, _fake_failure)
+    assert errors == 2
+
+
+def test_once_exit_nonzero_when_some_fail(tmp_config) -> None:
+    """Szenario: Teilweise fehlgeschlagen → Exit != 0."""
+    (tmp_config.paths.incoming / "ok.pdf").write_bytes(b"%PDF-1.4\n")
+    (tmp_config.paths.incoming / "bad.pdf").write_bytes(b"%PDF-1.4\n")
+
+    def mixed(src, *args, **kwargs):
+        if "bad" in src.name:
+            return _fake_failure(src, *args, **kwargs)
+        return _fake_success(src, *args, **kwargs)
+
+    errors = _run(tmp_config, mixed)
+    assert errors == 1
+
+
+def test_counters_track_success_and_failure(tmp_config) -> None:
+    """success_count und error_count sollen korrekt mitzählen."""
+    (tmp_config.paths.incoming / "ok.pdf").write_bytes(b"%PDF-1.4\n")
+    (tmp_config.paths.incoming / "bad.pdf").write_bytes(b"%PDF-1.4\n")
+
+    def mixed(src, *args, **kwargs):
+        if "bad" in src.name:
+            return _fake_failure(src, *args, **kwargs)
+        return _fake_success(src, *args, **kwargs)
+
+    with patch("pdf_ocr_hotfolder.service.check_preflight", return_value=None), \
+         patch("pdf_ocr_hotfolder.service.process_pdf", side_effect=mixed), \
+         patch("pdf_ocr_hotfolder.service._wait_until_stable", return_value=True):
+        service = HotfolderService(tmp_config)
+        try:
+            service.run_once()
+            assert service.success_count == 1
+            assert service.error_count == 1
+        finally:
+            service._executor.shutdown(wait=False)