## Problem
Running the full `UOContent.Tests` suite, the test host **hangs ~2.5 minutes at shutdown and then crashes** (`Test host process crashed` / run aborted). The tests themselves are fine — they complete in ~1s — but the process can't exit.
Captured via `--blame-hang` dump. The blocking thread:
```
System.Threading.WaitHandle.WaitOne()
Server.SerializationThreadWorker.Sleep() SerializationThreadWorker.cs:54 (_stopEvent.WaitOne())
Server.SerializationThreadWorker.Exit() SerializationThreadWorker.cs:61
Server.World.ExitSerializationThreads() World.cs:429
Server.Tests.UOContentFixture..ctor()
```
### Root cause
Both collection fixtures (`UOContentFixture` and `PathfindingTestFixture`) each run the **full process-global ModernUO bootstrap**. `World.Load()` is guarded to run once per process, so the **second** fixture's `World.Load()` is a no-op and does **not** respawn the serialization workers — but `World.ExitSerializationThreads()` is **not** guarded, so the second fixture calls `Exit()` on workers whose threads have already terminated. `Exit()` → `Sleep()` → `_stopEvent.WaitOne()` then blocks forever (a dead thread never sets the event). The first collection's tests run; the second collection's fixture deadlocks in its constructor; the host eventually gets killed.
This is why single-collection (filtered) runs were fine — only one fixture ever bootstraps — but the full suite hangs. It's not a parallelization race: even strictly sequential, the second fixture deadlocks.
## Fix
**(a) Engine — idempotent `SerializationThreadWorker.Exit()`**
A second `Exit()` is now a safe no-op instead of a permanent block. Only the owning (main) thread calls `Exit()`, so no synchronization is needed, and the single-call production shutdown path is unchanged.
**(b) Tests — one shared bootstrap, strictly sequential collections**
- New `TestServerBootstrap.EnsureInitialized()` runs the superset global init **exactly once per process** (lock + once-flag).
- `UOContentFixture` / `PathfindingTestFixture` slim down to delegate to it and no longer tear down global state (which the single-bootstrap model owns for the host's lifetime).
- `[assembly: CollectionBehavior(DisableTestParallelization = true)]` so collections never overlap.
## Result
| | Before | After |
|---|---|---|
| Tests run (full suite) | 258 (UOContent collection deadlocked) | **418** |
| Outcome | 2.5-min hang → host crash | **418 passed, clean exit** |
| Wall time | killed | **~7s** |
> [!IMPORTANT]
> **Breaking Changes**
> - DecodePacket and EncodePacket delegates replaced with IClientEncryption interface
> - NetState.Connection (Socket) replaced with internal RingSocket management
> - NetState.RecvPipe and NetState.SendPipe removed (buffers managed internally)
## Summary
Upgrades the networking stack from PollGroup-based I/O to io_uring, significantly improving I/O performance on Linux.
This also adds native client encryption support for encrypted UO clients.
## Major Changes
io_uring Networking Architecture
- Replaced PollGroup with IORingGroup for async socket I/O operations
- Removed Pipe.cs (mirrored ring buffer) and TcpServer.cs in favor of RingSocketManager
- Added NetState.Network.cs - centralized network infrastructure handling accept, recv, send, and disconnect
completions
- Added SocketHelper.cs - platform-specific socket utilities for raw socket handle operations (getpeername,
getsockname)
- Buffer management now handled by RingSocketManager with configurable slab allocation
### Client Encryption Support
- Added full encryption stack in Network/Encryption/:
- EncryptionConfig.cs - configurable encryption modes (None, Unencrypted, Encrypted, Both)
- EncryptionManager.cs - encryption detection and initialization for login/game packets
- LoginEncryption.cs - handles login packet encryption with version-derived keys
- GameEncryption.cs - handles game server encryption using Twofish
- TwofishEngine.cs - optimized Twofish block cipher implementation
- LoginKeys.cs - encryption key table for client versions
- IClientEncryption.cs - interface for client encryption implementations
### NetState Improvements
- Replaced Socket Connection with RingSocket _socket for managed socket lifecycle
- Changed from GCHandle polling to event-based completion processing
- Disconnect handling now properly waits for pending sends to flush
- Simplified connecting socket management using lazy queue removal
### Configuration
- New settings: network.encryptionMode and network.encryptionDebug
- Encryption mode flags: Unencrypted, Encrypted, or Both
### Dependencies
- Replaced PollGroup NuGet package with IORingGroup
- Linux requires liburing-dev / liburing-devel package
### Test plan
- Verify server starts and accepts connections on Linux with io_uring
- Verify server starts and accepts connections on Windows (fallback to IOCP)
- Test unencrypted client connections (ClassicUO with encryption disabled)
- Test encrypted client connections if available
- Verify graceful disconnect flushes pending data
- Confirm CI builds pass on all target platforms
### Summary
- Adds CanSpawnMobile(x, y, minZ, maxZ, canSwim, cantWalk, out spawnZ) overload for finding spawn surfaces within a Z range
- Adds CanSpawnItem(x, y, minZ, maxZ, out spawnZ) for item spawning with Surface+Impassable support (tables, furniture)
- Uses bitmask optimization inspired by Item.DropToWorld's m_OpenSlots pattern for O(1) surface/blocker checks
- HomeRange spawners now use surface detection to set proper Z bounds
### Key Changes
Map.cs:
- CanSpawnMobile with Z-range finds lowest valid surface for mobiles
- CanSpawnItem with Z-range finds lowest valid surface for items (including tables)
- CanFitItem for point-check item placement on Surface+Impassable tiles
- Bitmask approach eliminates nested loops and stackalloc arrays
Spawners:
- Simplified GetSpawnPosition using new Z-range methods
- HomeRange setter detects surface below spawner for proper Z bounds
- Consistent handling for mobiles and items
### Bug Fixes
- Water tiles (Impassable | Wet) no longer block swimming mobs
- Items can now spawn on tables/furniture (Surface+Impassable)
### Test Plan
- Run dotnet test - 631 tests pass
- Manual testing: multi-story spawning, water mobs, item spawning on tables
- Verify HomeRange spawner movement shifts bounds correctly
