Preserve original $schema version in ToJson() instead of forcing draft-04

[Copilot]

JsonSchema.ToJson() unconditionally overwrote SchemaVersion with "http://json-schema.org/draft-04/schema#" before serializing, discarding any version already present on the schema (e.g. 2020-12). This caused FromFileAsync() to appear to return a schema with the wrong version whenever the result was serialized.

Changes

• JsonSchema.cs: Changed ToJson(Formatting) to only apply the draft-04 default when SchemaVersion is null, leaving explicitly set versions intact.
• JsonSchemaTests.cs: Added test verifying that a schema declaring 2020-12 retains that version through a FromJsonAsync → ToJson round-trip.

// Before: always forced draft-04 regardless of what was in the file
SchemaVersion = "http://json-schema.org/draft-04/schema#";

// After: only applies draft-04 as default when no version is set
if (SchemaVersion == null)
{
    SchemaVersion = "http://json-schema.org/draft-04/schema#";
}

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• http://json-schema.org:80/draft-04/schema
  • Triggering command: /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net9.0/NJsonSchema.Tests /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net9.0/NJsonSchema.Tests @@ /tmp/tmpKLjJLR.tmp (http block)
  • Triggering command: /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests @@ /tmp/tmpiQ6LbH.tmp (http block)
  • Triggering command: /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests @@ /tmp/tmpVm5EzI.tmp (http block)
• schemas.sportradar.com
  • Triggering command: /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net9.0/NJsonSchema.Tests /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net9.0/NJsonSchema.Tests @@ /tmp/tmpKLjJLR.tmp (dns block)
  • Triggering command: /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests @@ /tmp/tmpiQ6LbH.tmp (dns block)
  • Triggering command: /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests /home/REDACTED/work/NJsonSchema/NJsonSchema/artifacts/bin/NJsonSchema.Tests/debug_net8.0/NJsonSchema.Tests @@ /tmp/tmpVm5EzI.tmp (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>FromFileAsync forces wrong json schema version</issue_title>
<issue_description>The json schema contains
{
"$schema": "https://json-schema.org/draft/2020-12"
...
}

However, when read from file via JsonSchema.FromFileAsync(), the output is
{
"$schema": "http://json-schema.org/draft-04/schema#",
...
}

Mismatch in version is causing anyOf to stop working.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes FromFileAsync forces wrong json schema version #1772

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