Action implementations for the notebook MCP tool (YmerNode.Mcp.Tools.Notebook, which calls run/2) — a thin boundary over YmerNode.Notebook and YmerNode.Notebook.Backup. This is a trust boundary: sql, table and id are guarded is_binary in each head because nothing downstream validates them — the MCP dispatch layer checks that a parameter is present but never what type it holds — so sql and table flow straight into SQLite and id flows into filename construction. Each action returns {:ok, data, hint_ctx} or {:error, {reason, ctx}} — and, where the error is one the caller can act on, {:error, {reason, ctx}, hint_ctx}, the three-element form that puts a follow-up hint on the error payload rather than only in its prose.

A wrong-typed value used to match no head at all and crash into the framework's top-level rescue, which told the caller only that a function clause did not match. Each guarded head now has an unguarded twin at the bottom of the module that answers {:wrong_type, …} instead, naming the key, the type wanted and what arrived. The guard is still what keeps the bad value out of SQLite and out of filename construction; the twin only makes the refusal readable.