Translates YmerNode.Notebook and YmerNode.Notebook.Backup error reasons into LLM-readable messages. SQLite errors are surfaced verbatim so the agent can read and fix its own SQL; backup failures never are, because their detail carries filesystem paths the caller must not see.

One reason reaches here from neither context: YmerNode.Mcp.Tools.Notebook.Actions refuses a parameter of the wrong type before either of them runs, and its message is the only thing that tells the caller which key to fix.