API endpoint for incremental ADIF download of a station's QSOs

[finlstrm]

Feature request: API endpoint for incremental ADIF download of a station's QSOs

Problem

There is currently no way for external software to download QSOs from Cloudlog through the API. Tools that want to keep a local log, back up contacts, or sync with another application have to use the manual ADIF export in the web interface, which needs a browser session and returns the whole logbook every time.

Proposed solution

Add an API endpoint that returns the QSOs of a single station location as ADIF, using a QSO-ID cursor so a client can fetch only contacts added since its last sync.

A client would:

1. Authenticate with an existing Cloudlog API key.
2. Request one of its station locations, starting from a cursor of 0.
3. Receive the ADIF, the number of QSOs returned, and the ID of the last QSO in the response.
4. Send that ID as the cursor on the next request, repeating while more records remain.

Requirements

• Uses existing API keys. Only active keys with read access are accepted. No new key system.
• Strict access control. A key can only export station locations owned by its user. Changing the station ID or cursor must never expose another user's data, and a nonexistent station must be indistinguishable from one the user doesn't own.
• Bounded responses. Page size is capped, and the response says whether more records are available.
• Valid ADIF. Reuses Cloudlog's existing ADIF generation so output matches the other exports.
• Predictable errors. JSON responses with appropriate HTTP status codes, following the existing API error format.
• No schema changes. No database migrations needed.

Out of scope

• Syncing edits or deletions of existing QSOs. The cursor only detects newly added contacts.
• Exporting several stations in one request.
• Exporting stations that are only shared with the user through a shared logbook.

Benefit

Lets third-party tools and scripts sync a logbook safely and efficiently, without a browser session or repeated full exports.