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/Controllers/API/GameSessions/V2/GameSessionsController.cs

@@ -0,0 +1,67 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using DorkNet.Models.GameSessions;
+using DorkNet.Server.Auth;
+using DorkNet.Server.Services;
+
+namespace DorkNet.Server.Controllers.API.GameSessions.V2;
+
+[ApiController]
+[Route("api/[controller]/v2")]
+[Authorize]
+public class GameSessionsController(GameSessionService sessionService) : ControllerBase
+{
+    private long CurrentPlayerId => this.RequireCurrentPlayerId();
+
+    [HttpPost("joinRandom")]
+    public async Task<ActionResult<JoinGameSessionResponse>> JoinRandom([FromBody] JoinRandomGameSessionRequest req)
+    {
+        var session = await sessionService.JoinOrCreateAsync(req.RoomId, req.ActivityLevelId, req.RegionId);
+        return Ok(new JoinGameSessionResponse
+        {
+            Result = JoinGameErrorCode.Success,
+            GameSession = session,
+        });
+    }
+
+    [HttpPost("joinById")]
+    public async Task<ActionResult<JoinGameSessionResponse>> JoinById([FromBody] JoinByIdRequest req)
+    {
+        var session = await sessionService.GetByIdAsync(req.GameSessionId);
+        if (session is null)
+        {
+            return Ok(new JoinGameSessionResponse { Result = JoinGameErrorCode.NotFound });
+        }
+
+        if (session.IsFull)
+        {
+            return Ok(new JoinGameSessionResponse { Result = JoinGameErrorCode.Full });
+        }
+
+        return Ok(new JoinGameSessionResponse
+        {
+            Result = JoinGameErrorCode.Success,
+            GameSession = session,
+        });
+    }
+
+    [HttpPost("leave")]
+    public async Task<ActionResult> Leave([FromBody] long sessionId)
+    {
+        await sessionService.PlayerLeftAsync(sessionId);
+        return Ok();
+    }
+
+    [HttpGet("{id:long}")]
+    public async Task<ActionResult<GameSession>> GetSession(long id)
+    {
+        var session = await sessionService.GetByIdAsync(id);
+        if (session is null) return NotFound();
+        return Ok(session);
+    }
+}
+
+public class JoinByIdRequest
+{
+    public long GameSessionId { get; set; }
+}