Handling of delete of non-existent leaf

[arnetheduck]

Consider the case where we issue a set_values with a delete of a leaf that is not in the triedb - is this a valid operation?

If it is a valid operation, it seems like it can fail to update branch pointers, like so:

• we traverse the trie and hit a branch node that shares path with the delete, the only item in changes:

  triedb/src/storage/engine/handlers.rs

  Line 109 in 66e5e07

  let result = self.handle_child_node_traversal(

• the next hop is a different page: https://github.com/base/triedb/blob/66e5e076e6e02f3030e1ea16343e0aca97b39248/src/storage/engine/handlers.rs#L168C30-L168C48
• set_values_in_page clones the page:

  triedb/src/storage/engine/write.rs

  Line 88 in 66e5e07

  let page = self.get_mut_clone(context, page_id)?;

• set_values_in_cloned_page loads the node (an account leaf for example) and decides they have no shared prefix (since the delete was for a node that doesn't exist) - notably, changes_left and changes_right are both empty:

  triedb/src/storage/engine/write.rs

  Line 192 in 66e5e07

  return self.set_values_in_cloned_page(

• recursion happens and returns NoChange:

  triedb/src/storage/engine/write.rs

  Line 170 in 66e5e07

  return Ok(PointerChange::None);

• NoChange bubbles up, but the page change that set_values_in_page caused with the clone+orphan is forgotten:

  triedb/src/storage/engine/handlers.rs

  Line 176 in 66e5e07

  match child_pointer_change {