# [Bug Report] ModelContextProtocol plugin causes Cook failure (ExitCode=1) when Editor is running
## Summary
When packaging from the Editor UI with the ModelContextProtocol (Unreal MCP) plugin enabled, the Cook process fails with `ExitCode=25 (Error_UnknownCookFailure)` despite the CookCommandlet itself completing successfully (result 0). This occurs because the MCP plugin attempts to start an HTTP server on the same port in both the Editor process and the Cook commandlet process.
## Engine Version
UE 5.8.0
## Steps to Reproduce
1. Enable the ModelContextProtocol plugin (Experimental)
2. Set `bAutoStartServer=True` in Project Settings (or via EditorPerProjectUserSettings.ini)
3. Open the Editor (MCP server starts on port 8000)
4. Package the project from Editor UI (File → Package Project → Windows)
5. Cook fails with ExitCode=1
## Expected Behavior
The Cook commandlet should not attempt to start the MCP HTTP server, as it serves no purpose during cooking.
## Actual Behavior
The `ModelContextProtocolEditor` module (Type: Editor) is loaded during the Cook commandlet. `SetupEditorIntegration()` calls `ShouldAutoStartServer()`, which reads `bAutoStartServer=True` from the ini and calls `StartServer(8000)`. Since the Editor already occupies port 8000, the bind fails and produces:
```
LogHttpListener: Error: HttpListener unable to bind to 127.0.0.1:8000
```
Because the Cook process is launched with `-CrashForUAT`, any Error-level log causes the process to exit with code 1, even though `CookCommandlet_0 finished execution (result 0)`.
## Relevant Code
`ModelContextProtocolEditor.cpp` → `SetupEditorIntegration()`:
```cpp
if (UE::ModelContextProtocol::ShouldAutoStartServer())
{
if (IModelContextProtocolModule\* Module = IModelContextProtocolModule::Get())
{
Module->StartServer(UE::ModelContextProtocol::GetServerPortNumber(), UE::ModelContextProtocol::GetServerUrlPath());
}
}
```
There is no `IsRunningCommandlet()` guard to skip server startup during commandlet execution.
## Suggested Fix
Add a commandlet check before starting the server:
```cpp
if (UE::ModelContextProtocol::ShouldAutoStartServer() && !IsRunningCommandlet())
{
*// ...*
}
```
## Workaround
Set `bAutoStartServer=False` in `EditorPerProjectUserSettings.ini` and add `-ModelContextProtocolStartServer` to the Editor launch arguments. This ensures only the interactive Editor starts the MCP server, while Cook and other commandlets skip it.
## Additional Context
- The `ModelContextProtocolEditor` module is declared as `“Type”: “Editor”` in the .uplugin, so it loads in any Editor-based process including commandlets.
- `-ModelContextProtocolPort=N` can override the port via command line, but there is no official ini-based hook to pass additional cooker options from the Editor packaging UI, making per-process port assignment impractical without a batch script.