Reorder MCP stdio launcher code

Keep the shared launcher API before the local implementation and move local launch helpers onto LocalStdioServerLauncher.\n\nCo-authored-by: Codex <noreply@openai.com>

Author: aibrahim-oai

codex-rs/rmcp-client/src/stdio_server_launcher.rs

@@ -13,8 +13,11 @@ use std::ffi::OsString;
 use std::io;
 use std::path::PathBuf;
 use std::process::Stdio;
+#[cfg(unix)]
 use std::thread::sleep;
+#[cfg(unix)]
 use std::thread::spawn;
+#[cfg(unix)]
 use std::time::Duration;
 
 #[cfg(unix)]
@@ -33,6 +36,8 @@ use tracing::warn;
 use crate::program_resolver;
 use crate::utils::create_env_for_mcp_server;
 
+// General purpose public code.
+
 /// Launches an MCP stdio server and returns the byte transport for rmcp.
 ///
 /// This trait is the boundary between MCP lifecycle code and process placement.
@@ -47,14 +52,6 @@ pub trait StdioServerLauncher: private::Sealed + Send + Sync {
     ) -> BoxFuture<'static, io::Result<LaunchedStdioServer>>;
 }
 
-/// Starts MCP stdio servers as local child processes.
-///
-/// This is the existing behavior for local MCP servers: the orchestrator
-/// process spawns the configured command and rmcp talks to the child's local
-/// stdin/stdout pipes directly.
-#[derive(Clone)]
-pub struct LocalStdioServerLauncher;
-
 /// Command-line process shape shared by stdio server launchers.
 #[derive(Clone)]
 pub struct StdioServerCommand {
@@ -81,23 +78,6 @@ pub(super) enum LaunchedStdioServerTransport {
     },
 }
 
-#[cfg(unix)]
-const PROCESS_GROUP_TERM_GRACE_PERIOD: Duration = Duration::from_secs(2);
-
-#[cfg(unix)]
-pub(super) struct ProcessGroupGuard {
-    process_group_id: u32,
-}
-
-#[cfg(not(unix))]
-pub(super) struct ProcessGroupGuard;
-
-mod private {
-    pub trait Sealed {}
-}
-
-impl private::Sealed for LocalStdioServerLauncher {}
-
 impl StdioServerCommand {
     /// Build the stdio process parameters before choosing where the process
     /// runs.
@@ -118,70 +98,102 @@ impl StdioServerCommand {
     }
 }
 
+// Local public implementation.
+
+/// Starts MCP stdio servers as local child processes.
+///
+/// This is the existing behavior for local MCP servers: the orchestrator
+/// process spawns the configured command and rmcp talks to the child's local
+/// stdin/stdout pipes directly.
+#[derive(Clone)]
+pub struct LocalStdioServerLauncher;
+
 impl StdioServerLauncher for LocalStdioServerLauncher {
     fn launch(
         &self,
         command: StdioServerCommand,
     ) -> BoxFuture<'static, io::Result<LaunchedStdioServer>> {
-        async move { launch_stdio_server_locally(command) }.boxed()
+        async move { Self::launch_server(command) }.boxed()
     }
 }
 
-fn launch_stdio_server_locally(command: StdioServerCommand) -> io::Result<LaunchedStdioServer> {
-    let StdioServerCommand {
-        program,
-        args,
-        env,
-        env_vars,
-        cwd,
-    } = command;
-    let program_name = program.to_string_lossy().into_owned();
-    let envs = create_env_for_mcp_server(env, &env_vars);
-    let resolved_program = program_resolver::resolve(program, &envs).map_err(io::Error::other)?;
-
-    let mut command = Command::new(resolved_program);
-    command
-        .kill_on_drop(true)
-        .stdin(Stdio::piped())
-        .stdout(Stdio::piped())
-        .env_clear()
-        .envs(envs)
-        .args(args);
-    #[cfg(unix)]
-    command.process_group(0);
-    if let Some(cwd) = cwd {
-        command.current_dir(cwd);
-    }
+// Local private implementation.
 
-    let (transport, stderr) = TokioChildProcess::builder(command)
-        .stderr(Stdio::piped())
-        .spawn()?;
-    let process_group_guard = transport.id().map(ProcessGroupGuard::new);
-
-    if let Some(stderr) = stderr {
-        tokio::spawn(async move {
-            let mut reader = BufReader::new(stderr).lines();
-            loop {
-                match reader.next_line().await {
-                    Ok(Some(line)) => {
-                        info!("MCP server stderr ({program_name}): {line}");
-                    }
-                    Ok(None) => break,
-                    Err(error) => {
-                        warn!("Failed to read MCP server stderr ({program_name}): {error}");
-                        break;
+#[cfg(unix)]
+const PROCESS_GROUP_TERM_GRACE_PERIOD: Duration = Duration::from_secs(2);
+
+#[cfg(unix)]
+pub(super) struct ProcessGroupGuard {
+    process_group_id: u32,
+}
+
+#[cfg(not(unix))]
+pub(super) struct ProcessGroupGuard;
+
+mod private {
+    pub trait Sealed {}
+}
+
+impl private::Sealed for LocalStdioServerLauncher {}
+
+impl LocalStdioServerLauncher {
+    fn launch_server(command: StdioServerCommand) -> io::Result<LaunchedStdioServer> {
+        let StdioServerCommand {
+            program,
+            args,
+            env,
+            env_vars,
+            cwd,
+        } = command;
+        let program_name = program.to_string_lossy().into_owned();
+        let envs = create_env_for_mcp_server(env, &env_vars);
+        let resolved_program =
+            program_resolver::resolve(program, &envs).map_err(io::Error::other)?;
+
+        let mut command = Command::new(resolved_program);
+        command
+            .kill_on_drop(true)
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .env_clear()
+            .envs(envs)
+            .args(args);
+        #[cfg(unix)]
+        command.process_group(0);
+        if let Some(cwd) = cwd {
+            command.current_dir(cwd);
+        }
+
+        let (transport, stderr) = TokioChildProcess::builder(command)
+            .stderr(Stdio::piped())
+            .spawn()?;
+        let process_group_guard = transport.id().map(ProcessGroupGuard::new);
+
+        if let Some(stderr) = stderr {
+            tokio::spawn(async move {
+                let mut reader = BufReader::new(stderr).lines();
+                loop {
+                    match reader.next_line().await {
+                        Ok(Some(line)) => {
+                            info!("MCP server stderr ({program_name}): {line}");
+                        }
+                        Ok(None) => break,
+                        Err(error) => {
+                            warn!("Failed to read MCP server stderr ({program_name}): {error}");
+                            break;
+                        }
                     }
                 }
-            }
-        });
-    }
+            });
+        }
 
-    Ok(LaunchedStdioServer {
-        transport: LaunchedStdioServerTransport::Local {
-            transport,
-            process_group_guard,
-        },
-    })
+        Ok(LaunchedStdioServer {
+            transport: LaunchedStdioServerTransport::Local {
+                transport,
+                process_group_guard,
+            },
+        })
+    }
 }
 
 impl ProcessGroupGuard {