fix(compiler): strip legacy brief: on entity update (parity with concept pages)

Author: KylinMountain

openkb/agent/compiler.py

@@ -933,6 +933,9 @@ def _build_frontmatter(sources: list[str]) -> str:
             fm = existing[:end + 3]
             fm = _set_fm_line(fm, "description", brief) if brief else fm
             fm = _set_fm_line(fm, "type", type_.capitalize()) if type_ else fm
+            # Drop any legacy ``brief:`` key (migrated to ``description:``),
+            # mirroring _write_concept's update path.
+            fm = re.sub(r"^brief:.*\n?", "", fm, flags=re.MULTILINE)
             existing = fm + "\n\n" + clean
         else:
             # Malformed/absent frontmatter (opening ``---`` with no closing

tests/test_compiler.py

@@ -758,6 +758,21 @@ def test_update_entity_capitalizes_type_and_writes_description(self, tmp_path):
         assert 'description: "b2"' in text
         assert "brief:" not in text
 
+    def test_update_entity_strips_legacy_brief(self, tmp_path):
+        entities = tmp_path / "entities"
+        entities.mkdir(parents=True)
+        (entities / "anthropic.md").write_text(
+            '---\nsources: ["summaries/a.md"]\ntype: organization\n'
+            'brief: Old brief.\n---\n\n# Anthropic\n\nOld.',
+            encoding="utf-8",
+        )
+        _write_entity(tmp_path, "anthropic", "# Anthropic\n\nv2.", "summaries/b.md",
+                      is_update=True, brief="New desc.", type_="organization")
+        text = (entities / "anthropic.md").read_text(encoding="utf-8")
+        assert "brief:" not in text
+        assert "Old brief." not in text
+        assert 'description: "New desc."' in text
+
 
 class TestBacklinkSummary:
     def test_adds_missing_concept_links(self, tmp_path):