feat(writer): add WriterState (cross-chapter regeneration tracking)

tests/test_phase5_writer_state.py

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+"""WriterState 测试（P5-T5）。"""
+from genesis.writer.writer_state import WriterState
+from genesis.writer.models import ChapterContent
+from genesis.eval.scorer import EvalReport
+
+
+def _content(cid, version=1):
+    return ChapterContent(chapter_id=cid, version=version, title="x", blocks=[])
+
+
+def _report(failed):
+    return EvalReport(
+        dimensions=[], total_score=0.0, passed=False, failed_chapters=failed,
+    )
+
+
+def test_initial_state_empty():
+    st = WriterState(["a", "b"])
+    assert st.needs_regeneration() == ["a", "b"]
+
+
+def test_record_success_clears_need():
+    st = WriterState(["a"])
+    st.record_success(_content("a"))
+    assert st.needs_regeneration() == []
+
+
+def test_failed_eval_marks_regeneration():
+    st = WriterState(["a"])
+    st.record_success(_content("a"))
+    st.record_eval("a", _report(["a"]))
+    assert st.needs_regeneration() == ["a"]