<!-- CURSOR_SUMMARY -->
> [!NOTE]
> **Medium Risk**
> Tightens validation on tool metadata, which may break existing tools
that relied on non-JSON-serializable `extras` values or keys; changes
are localized and well-covered by tests.
>
> **Overview**
> Adds **JSON-safety enforcement** for `ToolMetadata.extras`: top-level
keys must be strings at model construction, and `validate_for_tool()`
now recursively rejects non-JSON-native values (including non-finite
floats) with path-rich `ToolDefinitionError` messages.
>
> Expands tests to cover valid/invalid nested `extras` cases and
error-message quality, and bumps `arcade-core` version to `4.5.0`.
>
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2bab0db3c17f0ddb97868764d10494da543b39e5. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
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