create_link/update_link: data and tags fields cause 500 error, never persist (missing JSON stringification)

[karero]

Bug

create_link and update_link return an Internal Server Error whenever the request includes a data payload or tags array, and neither field is ever persisted -- even on calls where the error fires, other fields in the same request (e.g. title, subtitle) do still save correctly, so this isn't a total request failure, just these two fields.

Root cause (found in src/api-client.ts)

CreateLinkData/UpdateLinkData type data as Record<string, unknown> and tags as string[] (lines ~94-95, ~123-124), and the request body is stringified once as a whole:

...(body !== undefined ? { body: JSON.stringify(body) } : {}),

But per docs.grovs.io/docs/api-reference/generate-link, the underlying Grovs REST API expects data to be a stringified JSON string as its value (e.g. "data": "{\"screen\": \"promo\"}"), not a nested raw object. Stringifying the outer body once nests data as a raw object instead of double-encoding it as the API expects -- the MCP server is missing a JSON.stringify() pass on data (and apparently tags, which fails the same way) before it goes into the outer body.

Repro

Via the MCP tools directly:

1. update_link with only title/subtitle → succeeds, both persist (confirmed via get_link).
2. update_link with tags: ["referral"] alone → Internal Server Error; get_link afterward shows no tags field at all.
3. update_link with data: {"referralCode": "some-code"} alone → Internal Server Error; get_link afterward shows no data field at all.
4. name, title, subtitle, path, image_url all work individually and combined -- it's specifically data and tags that fail.

Suggested fix

Stringify data (and tags, if the REST API expects the same treatment there) individually before assembling the outer body, e.g.:

JSON.stringify({ ...rest, data: data ? JSON.stringify(data) : undefined })

Happy to help verify a fix against a real project if useful.