Fix relative stdio MCP cwd fallback (#19031)

codex-rs/app-server/src/codex_message_processor.rs

@@ -5802,8 +5802,8 @@ impl CodexMessageProcessor {
         let environment_manager = self.thread_manager.environment_manager();
         let runtime_environment = match environment_manager.default_environment() {
             Some(environment) => {
-                // Status listing has no turn cwd. This fallback is used only
-                // by executor-backed stdio MCPs whose config omits `cwd`.
+                // Status listing has no turn cwd. This fallback is used by
+                // stdio MCPs whose config omits `cwd`.
                 McpRuntimeEnvironment::new(environment, config.cwd.to_path_buf())
             }
             None => McpRuntimeEnvironment::new(

codex-rs/codex-mcp/src/mcp_connection_manager.rs

@@ -666,8 +666,8 @@ pub struct McpConnectionManager {
 /// servers should run for the current caller. Keep it explicit at manager
 /// construction time so status/snapshot paths and real sessions make the same
 /// local-vs-remote decision. `fallback_cwd` is not a per-server override; it is
-/// used only when an executor-backed stdio server omits `cwd` and the executor
-/// API still needs a concrete process working directory.
+/// used when a stdio server omits `cwd` and the launcher needs a concrete
+/// process working directory.
 #[derive(Clone)]
 pub struct McpRuntimeEnvironment {
     environment: Arc<Environment>,
@@ -1573,7 +1573,9 @@ async fn make_rmcp_client(
                     runtime_environment.fallback_cwd(),
                 ))
             } else {
-                Arc::new(LocalStdioServerLauncher) as Arc<dyn StdioServerLauncher>
+                Arc::new(LocalStdioServerLauncher::new(
+                    runtime_environment.fallback_cwd(),
+                )) as Arc<dyn StdioServerLauncher>
             };
 
             // `RmcpClient` always sees a launched MCP stdio server. The

codex-rs/core/tests/suite/rmcp_client.rs

@@ -618,6 +618,69 @@ async fn remote_stdio_server_uses_runtime_fallback_cwd_when_config_omits_cwd() -
     Ok(())
 }
 
+#[cfg(unix)]
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+#[serial(mcp_cwd)]
+async fn local_stdio_server_uses_runtime_fallback_cwd_when_config_omits_cwd() -> anyhow::Result<()>
+{
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let server_name = "rmcp_local_fallback_cwd";
+    let expected_cwd = Arc::new(Mutex::new(None::<PathBuf>));
+    let expected_cwd_for_config = Arc::clone(&expected_cwd);
+    let rmcp_test_server_bin = cargo_bin("test_stdio_server")?;
+    let relative_server_path = PathBuf::from("mcp-bin").join(
+        rmcp_test_server_bin
+            .file_name()
+            .expect("test stdio server binary should have a file name"),
+    );
+    let relative_command = relative_server_path.to_string_lossy().into_owned();
+
+    let fixture = test_codex()
+        .with_config(move |config| {
+            *expected_cwd_for_config
+                .lock()
+                .expect("expected cwd lock should not be poisoned") =
+                Some(config.cwd.to_path_buf());
+
+            let target_bin = config.cwd.join(&relative_server_path).into_path_buf();
+            let target_dir = target_bin
+                .parent()
+                .expect("relative test server path should include a parent");
+            fs::create_dir_all(target_dir).expect("create relative MCP bin directory");
+            fs::copy(&rmcp_test_server_bin, &target_bin).expect("copy test stdio server");
+
+            insert_mcp_server(
+                config,
+                server_name,
+                stdio_transport(
+                    relative_command,
+                    Some(HashMap::from([(
+                        "MCP_TEST_VALUE".to_string(),
+                        "local-fallback-cwd".to_string(),
+                    )])),
+                    Vec::new(),
+                ),
+                TestMcpServerOptions::default(),
+            );
+        })
+        .build(&server)
+        .await?;
+
+    let expected_cwd = expected_cwd
+        .lock()
+        .expect("expected cwd lock should not be poisoned")
+        .clone()
+        .expect("test config should record runtime fallback cwd");
+    let structured =
+        call_cwd_tool(&server, &fixture, server_name, "call-local-fallback-cwd").await?;
+
+    assert_cwd_tool_output(&structured, &expected_cwd);
+    server.verify().await;
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 1)]
 async fn stdio_mcp_tool_call_includes_sandbox_state_meta() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));

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

@@ -12,6 +12,7 @@
 
 use std::collections::HashMap;
 use std::ffi::OsString;
+use std::path::Path;
 
 /// Resolves a program to its executable path on Unix systems.
 ///
@@ -19,7 +20,11 @@ use std::ffi::OsString;
 /// the kernel's shebang (`#!`) mechanism, so this function simply returns
 /// the program name unchanged.
 #[cfg(unix)]
-pub fn resolve(program: OsString, _env: &HashMap<OsString, OsString>) -> std::io::Result<OsString> {
+pub fn resolve(
+    program: OsString,
+    _env: &HashMap<OsString, OsString>,
+    _cwd: &Path,
+) -> std::io::Result<OsString> {
     Ok(program)
 }
 
@@ -33,16 +38,16 @@ pub fn resolve(program: OsString, _env: &HashMap<OsString, OsString>) -> std::io
 /// This enables tools like `npx`, `pnpm`, and `yarn` to work correctly on Windows
 /// without requiring users to specify full paths or extensions in their configuration.
 #[cfg(windows)]
-pub fn resolve(program: OsString, env: &HashMap<OsString, OsString>) -> std::io::Result<OsString> {
-    // Get current directory for relative path resolution
-    let cwd = std::env::current_dir()
-        .map_err(|e| std::io::Error::other(format!("Failed to get current directory: {e}")))?;
-
+pub fn resolve(
+    program: OsString,
+    env: &HashMap<OsString, OsString>,
+    cwd: &Path,
+) -> std::io::Result<OsString> {
     // Extract PATH from environment for search locations
     let search_path = env.get(std::ffi::OsStr::new("PATH"));
 
     // Attempt resolution via which crate
-    match which::which_in(&program, search_path, &cwd) {
+    match which::which_in(&program, search_path, cwd) {
         Ok(resolved) => {
             tracing::debug!("Resolved {program:?} to {resolved:?}");
             Ok(resolved.into_os_string())
@@ -119,7 +124,7 @@ mod tests {
         let program = OsString::from(&env.program_name);
 
         // Apply platform-specific resolution
-        let resolved = resolve(program, &env.mcp_env)?;
+        let resolved = resolve(program, &env.mcp_env, std::env::current_dir()?.as_path())?;
 
         // Verify resolved path executes successfully
         let mut cmd = Command::new(resolved);

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

@@ -162,14 +162,27 @@ impl StdioServerCommand {
 /// process spawns the configured command and rmcp talks to the child's local
 /// stdin/stdout pipes directly.
 #[derive(Clone)]
-pub struct LocalStdioServerLauncher;
+pub struct LocalStdioServerLauncher {
+    fallback_cwd: PathBuf,
+}
+
+impl LocalStdioServerLauncher {
+    /// Creates a local stdio launcher.
+    ///
+    /// `fallback_cwd` is used when the MCP server config omits `cwd`, so
+    /// relative commands resolve from the caller's runtime working directory.
+    pub fn new(fallback_cwd: PathBuf) -> Self {
+        Self { fallback_cwd }
+    }
+}
 
 impl StdioServerLauncher for LocalStdioServerLauncher {
     fn launch(
         &self,
         command: StdioServerCommand,
     ) -> BoxFuture<'static, io::Result<StdioServerTransport>> {
-        async move { Self::launch_server(command) }.boxed()
+        let fallback_cwd = self.fallback_cwd.clone();
+        async move { Self::launch_server(command, fallback_cwd) }.boxed()
     }
 }
 
@@ -193,7 +206,10 @@ mod private {
 impl private::Sealed for LocalStdioServerLauncher {}
 
 impl LocalStdioServerLauncher {
-    fn launch_server(command: StdioServerCommand) -> io::Result<StdioServerTransport> {
+    fn launch_server(
+        command: StdioServerCommand,
+        fallback_cwd: PathBuf,
+    ) -> io::Result<StdioServerTransport> {
         let StdioServerCommand {
             program,
             args,
@@ -203,22 +219,21 @@ impl LocalStdioServerLauncher {
         } = command;
         let program_name = program.to_string_lossy().into_owned();
         let envs = create_env_for_mcp_server(env, &env_vars).map_err(io::Error::other)?;
+        let cwd = cwd.unwrap_or(fallback_cwd);
         let resolved_program =
-            program_resolver::resolve(program, &envs).map_err(io::Error::other)?;
+            program_resolver::resolve(program, &envs, &cwd).map_err(io::Error::other)?;
 
         let mut command = Command::new(resolved_program);
         command
             .kill_on_drop(true)
             .stdin(Stdio::piped())
             .stdout(Stdio::piped())
+            .current_dir(cwd)
             .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())

codex-rs/rmcp-client/tests/process_group_cleanup.rs

@@ -80,7 +80,7 @@ async fn drop_kills_wrapper_process_group() -> Result<()> {
         )])),
         &[],
         /*cwd*/ None,
-        Arc::new(LocalStdioServerLauncher),
+        Arc::new(LocalStdioServerLauncher::new(std::env::current_dir()?)),
     )
     .await?;
 

codex-rs/rmcp-client/tests/resources.rs

@@ -63,7 +63,7 @@ async fn rmcp_client_can_list_and_read_resources() -> anyhow::Result<()> {
         /*env*/ None,
         &[],
         /*cwd*/ None,
-        Arc::new(LocalStdioServerLauncher),
+        Arc::new(LocalStdioServerLauncher::new(std::env::current_dir()?)),
     )
     .await?;