refactor: extract chunk utils to domain/chunk_utils.py

- Extract safe_int, group_chunks_by_chapter, record_override_usage, chunk_text_for_tts
- Add tests/test_chunk_utils.py (15 tests)
- Update test_chunk_helpers.py and test_chunk_text_for_tts_prefers_raw.py imports
- conversion_runner.py: 1574 → 1518 lines
- All tests pass

tests/test_chunk_utils.py

@@ -0,0 +1,123 @@
+"""Tests for chunk processing utilities.
+
+Tests import from domain.chunk_utils (new location).
+"""
+
+from __future__ import annotations
+
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+
+# ---------------------------------------------------------------------------
+# safe_int
+# ---------------------------------------------------------------------------
+
+
+class TestSafeInt:
+    """safe_int safely converts to int with a default."""
+
+    def test_int_value(self):
+        from abogen.domain.chunk_utils import safe_int
+
+        assert safe_int(42) == 42
+
+    def test_string_number(self):
+        from abogen.domain.chunk_utils import safe_int
+
+        assert safe_int("7") == 7
+
+    def test_float_truncated(self):
+        from abogen.domain.chunk_utils import safe_int
+
+        assert safe_int(3.9) == 3
+
+    def test_none_returns_default(self):
+        from abogen.domain.chunk_utils import safe_int
+
+        assert safe_int(None) == 0
+
+    def test_garbage_returns_default(self):
+        from abogen.domain.chunk_utils import safe_int
+
+        assert safe_int("abc") == 0
+
+    def test_custom_default(self):
+        from abogen.domain.chunk_utils import safe_int
+
+        assert safe_int(None, default=-1) == -1
+
+
+# ---------------------------------------------------------------------------
+# chunk_text_for_tts (supplement existing tests)
+# ---------------------------------------------------------------------------
+
+
+class TestChunkTextForTts:
+    """chunk_text_for_tts selects the best text source."""
+
+    def test_non_mapping_returns_empty(self):
+        from abogen.domain.chunk_utils import chunk_text_for_tts
+
+        assert chunk_text_for_tts("not a dict") == ""
+
+    def test_none_returns_empty(self):
+        from abogen.domain.chunk_utils import chunk_text_for_tts
+
+        assert chunk_text_for_tts(None) == ""
+
+    def test_empty_dict_returns_empty(self):
+        from abogen.domain.chunk_utils import chunk_text_for_tts
+
+        assert chunk_text_for_tts({}) == ""
+
+    def test_whitespace_only_returns_empty(self):
+        from abogen.domain.chunk_utils import chunk_text_for_tts
+
+        assert chunk_text_for_tts({"text": "  "}) == ""
+
+
+# ---------------------------------------------------------------------------
+# record_override_usage
+# ---------------------------------------------------------------------------
+
+
+class TestRecordOverrideUsage:
+    """record_override_usage records pronunciation override usage."""
+
+    def test_noop_when_empty(self):
+        from abogen.domain.chunk_utils import record_override_usage
+
+        job = SimpleNamespace(language="en")
+        record_override_usage(job, {}, {})
+
+    def test_noop_when_all_zero(self):
+        from abogen.domain.chunk_utils import record_override_usage
+
+        job = SimpleNamespace(language="en")
+        record_override_usage(job, {"hello": 0}, {"hello": "hi"})
+
+    def test_records_usage(self):
+        from abogen.domain.chunk_utils import record_override_usage
+
+        job = SimpleNamespace(language="en", add_log=lambda *a, **kw: None)
+        with patch("abogen.domain.chunk_utils.increment_usage") as mock_inc:
+            record_override_usage(job, {"hello": 2}, {"hello": "hi"})
+            mock_inc.assert_called_once_with(language="en", token="hi", amount=2)
+
+    def test_fallback_token_from_normalized(self):
+        from abogen.domain.chunk_utils import record_override_usage
+
+        job = SimpleNamespace(language="ja", add_log=lambda *a, **kw: None)
+        with patch("abogen.domain.chunk_utils.increment_usage") as mock_inc:
+            record_override_usage(job, {"test": 1}, {})
+            mock_inc.assert_called_once_with(language="ja", token="test", amount=1)
+
+    def test_handles_exception_gracefully(self):
+        from abogen.domain.chunk_utils import record_override_usage
+
+        job = SimpleNamespace(language="en", add_log=lambda *a, **kw: None)
+        with patch("abogen.domain.chunk_utils.increment_usage", side_effect=RuntimeError("db error")):
+            record_override_usage(job, {"hello": 1}, {"hello": "hi"})