Prefixes from @context are ignored

https://github.com/spdx/spdx-java-v3jsonld-store/blob/f3b461971a7d5ea59569e3b1db5672ac57cd7cc2/src/main/java/org/spdx/v3jsonldstore/JsonLDDeserializer.java#L107

Prefixes from @context seem to be ignored, e.g.:

{
    "@context": {
        "xsd": "http://www.w3.org/2001/XMLSchema#",
        "spdx": "https://spdx.org/rdf/3.0.1/terms/Core/",
        # ...
    },
    # ...
    "spdx:spdxId": {
      "@type": "xsd:anyURI",
      "@value": "urn:uuid:01973600-280e-7e13-b035-87a63695cf3d"
    },
    # ...
}

does not work. spdxId only works with:

{
    "@context": {
        "xsd": "http://www.w3.org/2001/XMLSchema#",
        "@vocab": "https://spdx.org/rdf/3.0.1/terms/Core/",
        # ...
    },
    # ...
    "spdxId": {
      "@type": "xsd:anyURI",
      "@value": "urn:uuid:01973600-280e-7e13-b035-87a63695cf3d"
    },
    # ...
}

Here, it seems not specifying "@vocab": "https://spdx.org/rdf/3.0.1/terms/Core/", is also fine.

This leaves me also with the following questions:

Is this really a general purpose SPDX v3 JSON-LD store, or is it rather built to digest files from exactly one source that always structures them the same way? In RDF, I would expect an application to accept my files if the graph matches the necessary structure independent of the exact serialization i use. This seems not to be the case with this store.

Start with src/main/java/org/spdx/v3jsonldstore/JsonLDDeserializer.java at line 107 and trace how the @context entries are read when resolving prefixed properties. Reproduce the issue using the JSON-LD example in the report, then verify that prefixes such as spdx: and xsd: are handled as expected without relying on @vocab. Done means the reported prefixed form is accepted and covered by a regression test.