fix(mcp): default category-only search to observations, not entities

search_notes defaults entity_types to 'entity' when unset (issue #31), but categories only exist on observations — so search_notes(categories=[...]) without entity_types ANDed the category against entity rows (NULL category) and returned nothing. When categories is supplied without an explicit entity_types, default to observations instead. Adds a regression test for the categories-only path (Codex review on #908).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: phernandez <paul@basicmachines.co>

Author: phernandez

src/basic_memory/mcp/tools/search.py

@@ -1004,7 +1004,17 @@ async def search_notes(
                 # Applied after no_criteria() so that the implicit default doesn't
                 # mask a truly empty search request.
                 if not search_query.entity_types:
-                    search_query.entity_types = [SearchItemType("entity")]
+                    # Trigger: a category filter was supplied without an explicit
+                    #          entity_types.
+                    # Why: categories only exist on observations — defaulting to "entity"
+                    #      (whose rows have NULL category) would AND a category filter against
+                    #      entity rows and return nothing, defeating a category-only search.
+                    # Outcome: scope the implicit default to observations so
+                    #          search_notes(categories=[...]) returns the matching bullets.
+                    if search_query.categories:
+                        search_query.entity_types = [SearchItemType("observation")]
+                    else:
+                        search_query.entity_types = [SearchItemType("entity")]
 
                 logger.debug(
                     f"Search request: project={active_project.name} "

tests/mcp/test_tool_search.py

@@ -421,6 +421,42 @@ async def test_search_with_categories_filter(client, test_project):
     assert all("requirement" != r.get("category") for r in decision["results"])
 
 
+@pytest.mark.asyncio
+async def test_search_categories_without_entity_types_returns_observations(client, test_project):
+    """categories=[...] WITHOUT entity_types must return the matching observations (#908).
+
+    search_notes defaults entity_types to "entity" when unset, but categories only exist on
+    observations — so a category filter without an explicit entity_types would AND the
+    category against entity rows (which have NULL category) and return nothing. The implicit
+    default must scope to observations when categories is supplied.
+    """
+    await write_note(
+        project=test_project.name,
+        title="Category Default Note",
+        directory="test",
+        content=(
+            "# Category Default Note\n"
+            "- [requirement] Auth tokens must rotate every 24 hours\n"
+            "- [decision] We chose JWT for the auth token format\n"
+        ),
+    )
+
+    # Note: no entity_types passed — exercises the implicit default.
+    response = await search_notes(
+        project=test_project.name,
+        query="auth",
+        search_type="text",
+        categories=["requirement"],
+        output_format="json",
+    )
+
+    assert isinstance(response, dict), f"Search failed with error: {response}"
+    results = response["results"]
+    assert len(results) > 0, "category-only search must return matching observations"
+    assert all(r["type"] == "observation" for r in results)
+    assert all(r["category"] == "requirement" for r in results)
+
+
 @pytest.mark.asyncio
 async def test_search_with_date_filter(client, test_project):
     """Test search with date filter."""