feat: add option for custom docker host socket

Why:

The socket is different when we use rootless mode with docker.

mcontainer/cli.py

@@ -1347,6 +1347,9 @@ def add_mcp(
     env: List[str] = typer.Option(
         [], "--env", "-e", help="Environment variables (format: KEY=VALUE)"
     ),
+    docker_host: Optional[str] = typer.Option(
+        None, "--docker-host", help="Docker host socket file that should be mounted on the MCP container",
+    ),
     no_default: bool = typer.Option(
         False, "--no-default", help="Don't add MCP server to defaults"
     ),
@@ -1380,6 +1383,7 @@ def add_mcp(
                 proxy_options,
                 environment,
                 host_port,
+                docker_host,
                 add_as_default=not no_default,
             )
 

mcontainer/container.py

@@ -28,6 +28,7 @@ class ContainerManager:
     ):
         self.config_manager = config_manager or ConfigManager()
         self.session_manager = session_manager or SessionManager()
+
         self.user_config_manager = user_config_manager or UserConfigManager()
         self.mcp_manager = MCPManager(config_manager=self.user_config_manager)
 

mcontainer/mcp.py

@@ -179,6 +179,7 @@ class MCPManager:
         proxy_options: Dict[str, Any] = None,
         env: Dict[str, str] = None,
         host_port: Optional[int] = None,
+        docker_host: Optional[str] = None,
         add_as_default: bool = True,
     ) -> Dict[str, Any]:
         """Add a proxy-based MCP server.
@@ -191,6 +192,7 @@ class MCPManager:
             proxy_options: Options for the MCP proxy
             env: Environment variables to set in the container
             host_port: Host port to bind the MCP server to (auto-assigned if not specified)
+            docker_host: Docker host socket file that should be mounted on the MCP container
             add_as_default: Whether to add this MCP to the default MCPs list
 
         Returns:
@@ -223,6 +225,7 @@ class MCPManager:
             proxy_options=proxy_options or {},
             env=env or {},
             host_port=host_port,
+            docker_host=docker_host or "/var/run/docker.sock",
         )
 
         # Add to the configuration
@@ -570,7 +573,7 @@ ENTRYPOINT ["/entrypoint.sh"]
                     detach=True,
                     network=None,  # Start without network, we'll add it with aliases
                     volumes={
-                        "/var/run/docker.sock": {
+                        mcp_config.get("docker_host", "/var/run/docker.sock"): {
                             "bind": "/var/run/docker.sock",
                             "mode": "rw",
                         }

mcontainer/models.py

@@ -79,6 +79,7 @@ class ProxyMCP(BaseModel):
     proxy_options: Dict[str, Any] = Field(default_factory=dict)
     env: Dict[str, str] = Field(default_factory=dict)
     host_port: Optional[int] = None  # External port to bind the SSE port to on the host
+    docker_host: Optional[str] = None  # Docker host to use for the proxy container
 
 
 MCP = Union[RemoteMCP, DockerMCP, ProxyMCP]