test: cover brief() empty-palace and dedup behavior

Adds two tests to back the brief() retrieval mode:
- test_brief_empty_palace: verifies brief() surfaces L2's "no drawers"
  message instead of crashing when the palace has no data
- test_brief_dedupes_near_identical_drawers: verifies the >70% word
  overlap dedup actually collapses duplicates while preserving distinct
  content

Author: mvanhorn

tests/test_searcher.py

@@ -197,6 +197,30 @@ def test_brief(self, palace_path, seeded_collection):
         assert "Brief" in result
         assert "topics" in result
 
+    def test_brief_empty_palace(self, palace_path, collection):
+        """Brief surfaces the L2 'no drawers' message instead of crashing."""
+        result = brief(palace_path=palace_path)
+        assert result.startswith("No ")
+
+    def test_brief_dedupes_near_identical_drawers(self, palace_path, collection):
+        """Brief collapses drawers whose summary lines overlap heavily."""
+        collection.add(
+            ids=["dup_a", "dup_b", "distinct_c"],
+            documents=[
+                "The authentication module uses JWT tokens for session management.",
+                "The authentication module uses JWT tokens for session management.",
+                "Database migrations are handled by Alembic with PostgreSQL 15.",
+            ],
+            metadatas=[
+                {"wing": "project", "room": "backend", "source_file": "auth_a.py"},
+                {"wing": "project", "room": "backend", "source_file": "auth_b.py"},
+                {"wing": "project", "room": "backend", "source_file": "db.py"},
+            ],
+        )
+        result = brief(palace_path=palace_path, wing="project")
+        assert result.count("authentication module uses JWT") == 1
+        assert "Database migrations" in result
+
     def test_search_memories_query_error(self):
         """search_memories returns error dict when query raises."""
         mock_col = MagicMock()