fix: preserve custom frontmatter fields when updating notes

Fixes #36 by modifying entity_service.update_entity() to read existing
frontmatter from files before updating them. Custom metadata fields
such as Status, Priority, and Version are now preserved when notes
are updated through the write_note MCP tool.

Added test case that verifies this behavior by creating a note with
custom frontmatter and then updating it.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: phernandez

src/basic_memory/services/entity_service.py

@@ -141,10 +141,23 @@ async def update_entity(self, entity: EntityModel, schema: EntitySchema) -> Enti
         # Convert file path string to Path
         file_path = Path(entity.file_path)
 
+        # Read existing frontmatter from the file if it exists
+        existing_markdown = await self.entity_parser.parse_file(file_path)
+
+        # Create post with new content from schema
         post = await schema_to_markdown(schema)
+        
+        # Merge new metadata with existing metadata
+        existing_markdown.frontmatter.metadata.update(post.metadata)
+        
+        # Create a new post with merged metadata
+        merged_post = frontmatter.Post(
+            post.content,
+            **existing_markdown.frontmatter.metadata
+        )
 
         # write file
-        final_content = frontmatter.dumps(post, sort_keys=False)
+        final_content = frontmatter.dumps(merged_post, sort_keys=False)
         checksum = await self.file_service.write_file(file_path, final_content)
 
         # parse entity from file
@@ -309,4 +322,4 @@ async def update_entity_relations(
                 )
                 continue
 
-        return await self.repository.get_by_file_path(path)
+        return await self.repository.get_by_file_path(path)

tests/mcp/test_tool_notes.py

@@ -252,3 +252,72 @@ async def test_write_note_verbose(app):
         """).strip()
         in result
     )
+
+
+@pytest.mark.asyncio
+async def test_write_note_preserves_custom_metadata(app, test_config):
+    """Test that updating a note preserves custom metadata fields.
+    
+    Reproduces issue #36 where custom frontmatter fields like Status
+    were being lost when updating notes with the write_note tool.
+    
+    Should:
+    - Create a note with custom frontmatter
+    - Update the note with new content
+    - Verify custom frontmatter is preserved
+    """
+    # First, create a note with custom metadata using write_note
+    await write_note(
+        title="Custom Metadata Note",
+        folder="test",
+        content="# Initial content",
+        tags=["test"],
+    )
+    
+    # Read the note to get its permalink
+    content = await read_note("test/custom-metadata-note")
+    
+    # Now directly update the file with custom frontmatter
+    # We need to use a direct file update to add custom frontmatter
+    from pathlib import Path
+    import frontmatter
+    
+    file_path = test_config.home / "test" / "Custom Metadata Note.md"
+    post = frontmatter.load(file_path)
+
+    # Add custom frontmatter
+    post["Status"] = "In Progress"
+    post["Priority"] = "High"
+    post["Version"] = "1.0"
+    
+    # Write the file back
+    with open(file_path, "w") as f:
+        f.write(frontmatter.dumps(post))
+    
+    # Now update the note using write_note
+    result = await write_note(
+        title="Custom Metadata Note",
+        folder="test",
+        content="# Updated content",
+        tags=["test", "updated"],
+    )
+    
+    # Verify the update was successful
+    assert "Updated test/Custom Metadata Note.md" in result
+    
+    # Read the note back and check if custom frontmatter is preserved
+    content = await read_note("test/custom-metadata-note")
+    
+    # Custom frontmatter should be preserved
+    assert "Status: In Progress" in content
+    assert "Priority: High" in content
+    # Version might be quoted as '1.0' due to YAML serialization
+    assert "Version:" in content  # Just check that the field exists
+    assert "1.0" in content       # And that the value exists somewhere
+    
+    # And new content should be there
+    assert "# Updated content" in content
+    
+    # And tags should be updated
+    assert "'#test'" in content
+    assert "'#updated'" in content