The upstream .desktop file has a fallback to flatpack. It is only intended to run if `sparkleshare` isn't in the user's path. But to make matters even worse it will also run if `sparkleshare` exists with a failure code.
Remove this fallback to ensure that users don't download and run unpinned and untrusted code from the internet.
Sparkleshare requires 'sh' to be in its PATH, or push-operations fail. Its PATH consists of a single entry, which is configured in the postInstall phase. The bash-derivative includes 'sh', and adding it to the dependencies resolves the issue.
