virtual edges do not filter what protocols can be added to them

[Krastanov]

Virtual edges can have only a subset of all possible protocols.

This function https://github.com/QuantumSavory/QuantumSavory.jl/blob/0a57095c4930a4d2508623c5d3a6a9717911fec8/src/ProtocolZoo/ProtocolZoo.jl#L41 (permits_virtual_edge) can be used to filter the protocols that can be put on a virtual edge.

For instance in this picture, only EntanglementConsumer should be available in the dropdown:

[essenciary]

@Krastanov Maybe I'm not using this right, but the permits_virtual_edge method throws when passed some types of protocols. I can catch the exception and treat it as false but this will be computationally more expensive (though not a big deal, this API endpoint is very rarely used).

┌ Error: 2025-11-27 15:38:58 Unexpected error in /protocol_types
│   error =
│    MethodError: no method matching permits_virtual_edge(::Type{QuantumSavory.ProtocolZoo.CutoffProt})
│    The function `permits_virtual_edge` exists, but no method is defined for this combination of argument types.
│    
│    Closest candidates are:
│      permits_virtual_edge(::QuantumSavory.ProtocolZoo.EntanglementConsumer)
│       @ QuantumSavory ~/.julia/packages/QuantumSavory/lqOOH/src/ProtocolZoo/ProtocolZoo.jl:456
│      permits_virtual_edge(::QuantumSavory.ProtocolZoo.AbstractProtocol)
│       @ QuantumSavory ~/.julia/packages/QuantumSavory/lqOOH/src/ProtocolZoo/ProtocolZoo.jl:41
│    
│   stacktrace =
│    25-element Vector{Base.StackTraces.StackFrame}:
│     get_protocol_types() at parser.jl:209
│     ⋮
└ @ Cqn ~/Projects/cqn-api/src/errors.jl:48

[essenciary]

I think that the issue is that permits_virtual_edge expects instances, instead of the types.

[essenciary]

Anyway, I'm leaving the code as is for now, with the try/catch and false on exception. Right now all are false since the method throws for any type of protocol. But if you fix it, this will work correctly and won't throw anymore.

[Krastanov]

It should be giving true for EntanglementConsumer and pretty much nothing else right now.

If it is throwing, that is indeed a QuantumSavory bug. Please just proceed with your try/catch solution, I will clean it up on the QuantumSavory side in the future.

[Krastanov]

And I will also fix it to work both on instances and types. So no need to change anything on your end.

[protozoo]

Fronte-end part of this fix is tracked in this other issue: #72