Import december-2020-12-18 from private repo (scrubbed 2026-05-27)

Targets Rec Room 2020.12.18 client.

Re-import after adding:
- DorkNet.ClientMod/dorknet-clientmod.json.template — config schema
  the launcher's manifest-driven patcher renders into UserData/.
- tools/build-patcher-zip.ps1 — produces the dorknet-clientpatch-{key}.zip
  Release asset the launcher fetches.
- .github/workflows/release.yml — auto-publishes both Release assets
  on v1-december-* tag push.

Scrubbed via maintainer-side scrub-for-public.ps1: same drop rules as
the prior import, plus build-patcher-zip.ps1 added to the tools/
allow-list so it survives the scrub.

DorkNet.Server/Services/DomainConfig.cs

@@ -0,0 +1,18 @@
+namespace DorkNet.Server.Services;
+
+/// <summary>Single source of truth for the deployment apex domain.
+/// Read from <c>DORKNET_DOMAIN</c> env var (or config key
+/// <c>Domain:Apex</c>) at startup. Defaults to <c>localhost</c>. Replaces
+/// per-controller <c>[Host("api.rec.net","api.localhost")]</c> filters —
+/// allowed hosts are derived as <c>{apex}</c> + <c>*.{apex}</c>, fed
+/// into HostFilteringMiddleware. Subdomain-discriminating handlers
+/// (Cdn vs Img on path "/{*path}") branch on
+/// <c>Request.Host.Host.Split('.')[0]</c>.</summary>
+public sealed class DomainConfig
+{
+    public string Apex { get; }
+    public DomainConfig(string apex) { Apex = apex; }
+    public string Sub(string prefix) => $"{prefix}.{Apex}";
+    public static bool MatchesSubdomain(string host, string prefix)
+        => host.StartsWith(prefix + ".", StringComparison.OrdinalIgnoreCase);
+}