[uss_qualifier] enable testing of requirements regarding interactions between participants and DSS instances #1039
Description
uss_qualifier is currently unable to validate requirements such as NetRID-NET0620[1], as it would require the uss_qualifier to be able to force the failure of a request a USS makes to the DSS.
A possible solution would involve a mock DSS instance, or a real DSS under the qualifier's control and which can selectively fail requests, but this goes against the stance that uss_qualifier should be as uninvasive as possible with respect to the real-world ecosystem in which tests are run.
A viable alternative would be to have uss_qualifier act as a proxy to a real DSS instance, and to temporarily configure the systems under test to use such a proxy.[2]
This would allow the qualifier to selectively fail requests to the DSS and otherwise observe all requests from a USS to the DSS.
An important requirement of such a proxy is that it should not meaningfully increase the latency of a request.
Note: this is rather low priority. this issue is here to capture a discussion we had during the weekly meeting on the 3rd of June 2025
[1]: a USS failing to create an ISA on the DSS should notify the operator
[2]: this assumes that USSes interact with DSS exclusively via the official API. One could imagine that a USS that also operates a DSS instance might chose not to do so, but this