Useful for confirming that ``YNAB_API_KEY`` is set and valid without
touching budget data.

Enabled by default. Mutating calls require ``code_mode_mutations_enabled`` preference
and must use ``ynab.write.*``. The snippet is treated as the body of an async function:
``await ynab.read.get_budgets()``, ``return`` directly.

The snippet runs in a sandboxed environment with a ``spec`` variable — a list of dicts,
each with keys ``name``, ``namespace`` (``"read"`` or ``"write"``), ``signature``,
``doc``, and ``returns``. Filter or map ``spec`` and return the subset you need.

Example: ``return [t for t in spec if "transaction" in t["name"]]``

No live YNAB API access. Returns the same CodeModeResult shape as execute.

The token is persisted in the platform keychain (macOS Keychain,
Windows Credential Locker, or Linux Secret Service) under
service=``mcp-ynab`` user=``YNAB_API_KEY``. After this returns, future
requests in this process and future runs will pick the key up via
``_resolve_api_key`` — though the ``YNAB_API_KEY`` env var still wins
if it is set.

Reads the in-memory ``ynab_resources.preferences`` (which already reflects
the env > preferences.json > defaults source order). The same content is
available as a resource at ``ynab://preferences`` for clients that prefer
to read it that way.

``name`` must be one of the ``Preferences`` model fields:
``default_budget_id``, ``category_cache_ttl_minutes``, or
``confirm_before_post``. Bool values accept any of
``1/0/true/false/yes/no/on/off`` (case-insensitive). The empty string is
the documented way to clear ``default_budget_id`` (stored as ``None``);
on a non-Optional field it surfaces as a coercion error.

Note: changes to ``default_budget_id`` here are equivalent to calling
``set_preferred_budget_id``; both write the same field.