Found by driving the published server over real stdio JSON-RPC rather than importing its functions —
which is the only way to see what a client actually receives.

**Our errors reached the agent blank.** The SDK wraps any exception it did not raise in a ToolError
whose message is exactly `Error executing tool <name>`; the detail is dropped. So a missing folder
and a path that escaped the named folder arrived as the same six words, while the SDK's own argument
validation returned "Input should be a valid list". An agent told only that something went wrong
cannot retry — it gives up, or it invents, which is the failure this package exists to prevent
happening to the tool that is supposed to catch it.

Path errors now return the reason as data, readable on both mcp 1.x and 2.x without depending on
which exception type the framework lets through. Anything we did not write still escapes: a message
we cannot vouch for is not one to hand an agent.

**`serverInfo.version` was an empty string** in the initialize handshake — the first thing a client
sees, and Cursor shows it. It now reports the package version.

Pins move to core>=0.3.3 and cli>=0.2.3.