Use shell to launch MCP and ACP servers (#42382)

`npx`, and any `npm install`-ed programs, exist as batch
scripts/PowerShell scripts on the PATH. We have to use a shell to launch
these programs.

Fixes https://github.com/zed-industries/zed/issues/41435
Closes https://github.com/zed-industries/zed/pull/42651


Release Notes:

- windows: Custom MCP and ACP servers installed through `npm` now launch
correctly.

---------

Co-authored-by: Lukas Wirth <me@lukaswirth.dev>

crates/agent_servers/src/acp.rs

@@ -9,6 +9,10 @@ use futures::io::BufReader;
 use project::Project;
 use project::agent_server_store::AgentServerCommand;
 use serde::Deserialize;
+use settings::Settings as _;
+use task::ShellBuilder;
+#[cfg(windows)]
+use task::ShellKind;
 use util::ResultExt as _;
 
 use std::path::PathBuf;
@@ -21,7 +25,7 @@ use gpui::{App, AppContext as _, AsyncApp, Entity, SharedString, Task, WeakEntit
 
 use acp_thread::{AcpThread, AuthRequired, LoadError, TerminalProviderEvent};
 use terminal::TerminalBuilder;
-use terminal::terminal_settings::{AlternateScroll, CursorShape};
+use terminal::terminal_settings::{AlternateScroll, CursorShape, TerminalSettings};
 
 #[derive(Debug, Error)]
 #[error("Unsupported version")]
@@ -86,9 +90,26 @@ impl AcpConnection {
         is_remote: bool,
         cx: &mut AsyncApp,
     ) -> Result<Self> {
-        let mut child = util::command::new_smol_command(&command.path);
+        let shell = cx.update(|cx| TerminalSettings::get(None, cx).shell.clone())?;
+        let builder = ShellBuilder::new(&shell, cfg!(windows));
+        #[cfg(windows)]
+        let kind = builder.kind();
+        let (cmd, args) = builder.build(Some(command.path.display().to_string()), &command.args);
+
+        let mut child = util::command::new_smol_command(cmd);
+        #[cfg(windows)]
+        if kind == ShellKind::Cmd {
+            use smol::process::windows::CommandExt;
+            for arg in args {
+                child.raw_arg(arg);
+            }
+        } else {
+            child.args(args);
+        }
+        #[cfg(not(windows))]
+        child.args(args);
+
         child
-            .args(command.args.iter().map(|arg| arg.as_str()))
             .envs(command.env.iter().flatten())
             .stdin(std::process::Stdio::piped())
             .stdout(std::process::Stdio::piped())

crates/agent_servers/src/custom.rs

@@ -114,7 +114,6 @@ impl AgentServer for CustomAgentServer {
         let default_model = self.default_model(cx);
         let store = delegate.store.downgrade();
         let extra_env = load_proxy_env(cx);
-
         cx.spawn(async move |cx| {
             let (command, root_dir, login) = store
                 .update(cx, |store, cx| {