Add Linux game server fallback packaging

Docs/Ops/DedicatedServerBuildRunbook.md

@@ -60,9 +60,31 @@ Expected output:
 - Logs: `Saved\BuildLogs\BuildLinuxDedicatedServer.log`
 - Archive: `Builds\LinuxServerDevelopment`
 
-If the script fails before compile with a Linux toolchain error, install Epic's
-Unreal `5.7` Linux cross-compile toolchain on Windows-Builder, reopen the
-terminal, and run the script again.
+The script self-heals `LINUX_MULTIARCH_ROOT` when the known UE 5.7 toolchain is
+installed at `C:\UnrealToolchains\v26_clang-20.1.8-rockylinux8`.
+
+If the script fails with:
+
+```text
+Server targets are not currently supported from this engine distribution.
+```
+
+the installed Epic binary engine cannot build the true `AgrarianGameServer`
+target. Use the MVP fallback package until a source-built/server-capable engine
+is available:
+
+```bat
+cd /d P:\AgrarianGameBulid
+Scripts\PackageLinuxGameServerFallback-Windows.bat
+```
+
+Fallback expected output:
+
+- Logs: `Saved\BuildLogs\PackageLinuxGameServerFallback.log`
+- Archive: `Builds\LinuxGameDevelopment`
+
+Deploy the fallback package to `/opt/agrarian/server` and launch it through
+`AgrarianGameServer.sh` with `-server -port=7777 -NullRHI -nosound`.
 
 ## Initial Runtime Shape