feat(skill-learning): add draft preservation checks

app-instance/backend/tests/unit/test_skill_learning_preservation.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from beaver.skills.learning.preservation import check_preservation
+
+
+def test_preservation_passes_when_base_sections_remain() -> None:
+    base = "# Skill\n\n## Workflow\n\n- Read first.\n\n## Safety\n\n- Do not delete files.\n"
+    draft = "# Skill\n\n## Workflow\n\n- Read first.\n- Then write.\n\n## Safety\n\n- Do not delete files.\n"
+
+    report = check_preservation(base_content=base, draft_content=draft)
+
+    assert report["passed"] is True
+    assert report["risk_level"] == "low"
+    assert "Workflow" in report["preserved_sections"]
+    assert "Safety" in report["preserved_sections"]
+    assert report["dropped_sections"] == []
+
+
+def test_preservation_flags_dropped_section() -> None:
+    base = "# Skill\n\n## Workflow\n\n- Read first.\n\n## Safety\n\n- Do not delete files.\n"
+    draft = "# Skill\n\n## Workflow\n\n- Read first.\n"
+
+    report = check_preservation(base_content=base, draft_content=draft)
+
+    assert report["passed"] is False
+    assert report["risk_level"] == "high"
+    assert "Safety" in report["dropped_sections"]