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/Compat/HttpContextExtensions.cs

@@ -0,0 +1,29 @@
+using Microsoft.AspNetCore.Http;
+
+namespace DorkNet.Server.Compat;
+
+/// <summary>Helpers to read the active <see cref="ClientVersion"/>
+/// off the current request. The version is set by
+/// <c>VersionDetectionMiddleware</c> early in the pipeline so any
+/// downstream consumer (controllers, services, filters) can resolve
+/// it without re-parsing the header.</summary>
+public static class HttpContextExtensions
+{
+    private const string ClientVersionKey = "DorkNet.ClientVersion";
+
+    /// <summary>Stamp the resolved version on the request. Called by
+    /// <c>VersionDetectionMiddleware</c>; not for general use.</summary>
+    internal static void SetClientVersion(this HttpContext ctx, ClientVersion v)
+        => ctx.Items[ClientVersionKey] = v;
+
+    /// <summary>The client version for this request. Returns
+    /// <see cref="ClientVersion.Unknown"/> if the middleware hasn't
+    /// run (e.g. a unit test that calls a controller method directly)
+    /// rather than null, so callers can safely branch on
+    /// <c>Generation</c> without null-checks.</summary>
+    public static ClientVersion ClientVersion(this HttpContext ctx)
+        => ctx.Items.TryGetValue(ClientVersionKey, out var v)
+           && v is ClientVersion cv
+            ? cv
+            : Compat.ClientVersion.Unknown;
+}