Unix Domain Socket auto discovery (#833)

This PR adds end-to-end Unix domain socket (UDS) support, allowing zen CLI to discover and connect to UDS-only servers automatically.

- **`unix://` URI scheme in zen CLI**: The `-u` / `--hosturl` option now accepts `unix:///path/to/socket` to connect to a zenserver via a Unix domain socket instead of TCP.
- **Per-instance shared memory for extended server info**: Each zenserver instance now publishes a small shared memory section (keyed by SessionId) containing per-instance data that doesn't fit in the fixed-size ZenServerEntry -- starting with the UDS socket path. This is a 4KB pagefile-backed section on Windows (`Global\ZenInstance_{sessionid}`) and a POSIX shared memory object on Linux/Mac (`/UnrealEngineZen_{sessionid}`).
- **Client-side auto-discovery of UDS servers**: `zen info`, `zen status`, etc. now automatically discover and prefer UDS connections when a server publishes a socket path. Servers running with `--no-network` (UDS-only) are no longer invisible to the CLI.
- **`kNoNetwork` flag in ZenServerEntry**: Servers started with `--no-network` advertise this in their shared state entry. Clients skip TCP fallback for these servers, and display commands (`ps`, `status`, `top`) show `-` instead of a port number to indicate TCP is not available.

3 files changed, 26 insertions, 4 deletions

diff --git a/src/zenserver/config/config.cpp b/src/zenserver/config/config.cpp
index 8118cb424..60ae93853 100644
--- a/src/zenserver/config/config.cpp
+++ b/src/zenserver/config/config.cpp
@@ -201,6 +201,7 @@ struct ZenServerCmdLineOptions
 	std::string DataDir;
 	std::string BaseSnapshotDir;
 	std::string SecurityConfigPath;
+	std::string UnixSocketPath;
 	std::string PortStr;
 
 	ZenLoggingCmdLineOptions LoggingOptions;
@@ -320,7 +321,7 @@ ZenServerCmdLineOptions::AddCliOptions(cxxopts::Options& options, ZenServerConfi
 					   "",
 					   "unix-socket",
 					   "Unix domain socket path to listen on (in addition to TCP)",
-					   cxxopts::value<std::string>(ServerOptions.HttpConfig.UnixSocketPath),
+					   cxxopts::value<std::string>(UnixSocketPath),
 					   "<path>");
 
 	options.add_option("network",
@@ -480,6 +481,11 @@ ZenServerCmdLineOptions::ApplyOptions(cxxopts::Options& options, ZenServerConfig
 	ServerOptions.BaseSnapshotDir	 = MakeSafeAbsolutePath(BaseSnapshotDir);
 	ServerOptions.SecurityConfigPath = MakeSafeAbsolutePath(SecurityConfigPath);
 
+	if (!UnixSocketPath.empty())
+	{
+		ServerOptions.HttpConfig.UnixSocketPath = MakeSafeAbsolutePath(UnixSocketPath);
+	}
+
 	if (PortStr != "auto")
 	{
 		int Port	   = 0;
diff --git a/src/zenserver/zenserver.cpp b/src/zenserver/zenserver.cpp
index 8283f0cbe..519176ffe 100644
--- a/src/zenserver/zenserver.cpp
+++ b/src/zenserver/zenserver.cpp
@@ -726,6 +726,20 @@ ZenServerMain::Run()
 
 		Entry = ServerState.Register(m_ServerOptions.BasePort);
 
+		// Publish per-instance extended info (e.g. UDS path) via a small shared memory
+		// section keyed by SessionId so clients can discover it during Snapshot() enumeration.
+		{
+			InstanceInfoData InstanceData;
+			InstanceData.UnixSocketPath = m_ServerOptions.HttpConfig.UnixSocketPath;
+			m_InstanceInfo.Create(GetSessionId(), InstanceData);
+			Entry->SignalHasInstanceInfo();
+		}
+
+		if (m_ServerOptions.HttpConfig.NoNetwork)
+		{
+			Entry->SignalNoNetwork();
+		}
+
 		if (m_ServerOptions.OwnerPid)
 		{
 			// We are adding a sponsor process to our own entry, can't wait for pick since the code is not run until later
@@ -786,7 +800,8 @@ ZenServerMain::MakeLockData(bool IsReady)
 								.EffectiveListenPort = gsl::narrow<uint16_t>(m_ServerOptions.BasePort),
 								.Ready				 = IsReady,
 								.DataDir			 = m_ServerOptions.DataDir,
-								.ExecutablePath		 = GetRunningExecutablePath()});
+								.ExecutablePath		 = GetRunningExecutablePath(),
+								.UnixSocketPath		 = m_ServerOptions.HttpConfig.UnixSocketPath});
 };
 
 }  // namespace zen
diff --git a/src/zenserver/zenserver.h b/src/zenserver/zenserver.h
index 374184aa9..830f36e54 100644
--- a/src/zenserver/zenserver.h
+++ b/src/zenserver/zenserver.h
@@ -148,8 +148,9 @@ public:
 	ZenServerMain& operator=(const ZenServerMain&) = delete;
 
 protected:
-	ZenServerConfig& m_ServerOptions;
-	LockFile		 m_LockFile;
+	ZenServerConfig&	  m_ServerOptions;
+	LockFile			  m_LockFile;
+	ZenServerInstanceInfo m_InstanceInfo;
 
 	virtual void InitializeLogging();
 	virtual void DoRun(ZenServerState::ZenServerEntry* Entry) = 0;