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/IVersionPlugin.cs

@@ -0,0 +1,39 @@
+namespace DorkNet.Server.Compat;
+
+/// <summary>One client-version-family plugin. Each implementation
+/// declares which exact version <see cref="VersionKeys"/> it handles
+/// and which protocol-compatibility <see cref="Generation"/> they map
+/// to. The plugin's job at registration time is to also wire any
+/// generation-specific strategy services into DI via
+/// <see cref="RegisterStrategies"/> so controllers / services
+/// downstream can resolve the right <c>IWireFormat</c>,
+/// <c>IRouteOverride</c>, etc. for the active request's generation.
+///
+/// <para>Adding a new version with the SAME wire shapes as an existing
+/// generation = just listing its key in that generation's plugin
+/// <see cref="VersionKeys"/>. Only a new generation needs new
+/// strategy classes.</para>
+/// </summary>
+public interface IVersionPlugin
+{
+    /// <summary>All client-build keys this plugin handles. Multiple
+    /// keys can share one plugin when several Rec Room builds shipped
+    /// the same wire format. Convention: lowercase, underscore-separated,
+    /// matching the literal the client mod sends in
+    /// <c>X-DorkNet-Version</c>.</summary>
+    IReadOnlyCollection<string> VersionKeys { get; }
+
+    /// <summary>Wire-format-compatibility group this plugin implements.
+    /// Multiple plugins can share a generation (rare, but allowed when
+    /// e.g. a Quest build and a PC build of the same era are
+    /// protocol-identical and we just want separate
+    /// <see cref="VersionKeys"/> bookkeeping).</summary>
+    string Generation { get; }
+
+    /// <summary>Register any generation-specific strategy services
+    /// into DI. Called once at startup by the bootstrap code in
+    /// <c>Program.cs</c>. Use keyed registrations (keyed by
+    /// <see cref="Generation"/>) so requests for other generations
+    /// don't collide.</summary>
+    void RegisterStrategies(IServiceCollection services);
+}