Guid parameters generate an object schema although profiles read GUID strings #701

Problem

Fallout 10.4.0 and current develop describe Guid parameters as reflected objects. System.Text.Json reads the same parameter from a JSON string. Editors therefore reject the value the build accepts. Nullable Guid also loses its nullable string shape.

Reproduction

Add these parameters to a FalloutBuild:

[Parameter] readonly Guid Id;
[Parameter] readonly Guid? OptionalId;
[Parameter] readonly Guid[] Ids;

Run any target and inspect .fallout/build.schema.json. The fields reference definitions.Guid, which contains object properties such as Variant and Version. A profile entry such as "Id": "70d8a2ef-dbbd-4e74-bca9-9a7e1867f97b" loads at runtime.

Outcome

Generate the same string representation the runtime reads, including nullable, array and nested values. Consumers should not rewrite the generated schema.

Acceptance criteria

• Guid parameters generate a string schema with GUID format information.
• Guid? allows both a GUID string and null.
• Guid arrays and nested properties use that same shape.
• Runtime profile loading continues to accept GUID strings.

Notes

I have a local generator fix and regression tests. All 254 Fallout.Build.Specs tests passed on Windows. The GUID check fails against the original mapper. This can accompany the profile-loading correction discussed in #667 (Enumeration profile loading).