Bridge command generation to powershell when on Windows (#2319)

## What? Why? How?
- When running on Windows, codex often tries to invoke bash commands,
which commonly fail (unless WSL is installed)
- Fix: Detect if powershell is available and, if so, route commands to
it
- Also add a shell_name property to environmental context for codex to
default to powershell commands when running in that environment

## Testing
- Tested within WSL and powershell (e.g. get top 5 largest files within
a folder and validated that commands generated were powershell commands)
- Tested within Zsh
- Updated unit tests

---------

Co-authored-by: Eddy Escardo <eddy@openai.com>

codex-rs/Cargo.lock

@@ -737,6 +737,7 @@ dependencies = [
  "tree-sitter-bash",
  "uuid",
  "walkdir",
+ "which",
  "whoami",
  "wildmatch",
  "wiremock",
@@ -5599,6 +5600,18 @@ version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a751b3277700db47d3e574514de2eced5e54dc8a5436a3bf7a0b248b2cee16f3"
 
+[[package]]
+name = "which"
+version = "6.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b4ee928febd44d98f2f459a4a79bd4d928591333a494a10a868418ac1b39cf1f"
+dependencies = [
+ "either",
+ "home",
+ "rustix 0.38.44",
+ "winsafe",
+]
+
 [[package]]
 name = "whoami"
 version = "1.6.0"
@@ -6011,6 +6024,12 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "winsafe"
+version = "0.0.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d135d17ab770252ad95e9a872d365cf3090e3be864a34ab46f48555993efc904"
+
 [[package]]
 name = "wiremock"
 version = "0.6.4"

codex-rs/core/Cargo.toml

@@ -71,6 +71,9 @@ openssl-sys = { version = "*", features = ["vendored"] }
 [target.aarch64-unknown-linux-musl.dependencies]
 openssl-sys = { version = "*", features = ["vendored"] }
 
+[target.'cfg(target_os = "windows")'.dependencies]
+which = "6"
+
 [dev-dependencies]
 assert_cmd = "2"
 core_test_support = { path = "tests/common" }

codex-rs/core/src/codex.rs

@@ -511,6 +511,7 @@ impl Session {
             turn_context.cwd.to_path_buf(),
             turn_context.approval_policy,
             turn_context.sandbox_policy.clone(),
+            sess.user_shell.clone(),
         )));
         sess.record_conversation_items(&conversation_items).await;
 
@@ -1070,6 +1071,7 @@ async fn submission_loop(
                         new_cwd,
                         new_approval_policy,
                         new_sandbox_policy,
+                        sess.user_shell.clone(),
                     ))])
                     .await;
                 }
@@ -2051,18 +2053,20 @@ pub struct ExecInvokeArgs<'a> {
     pub stdout_stream: Option<StdoutStream>,
 }
 
-fn maybe_run_with_user_profile(
+fn maybe_translate_shell_command(
     params: ExecParams,
     sess: &Session,
     turn_context: &TurnContext,
 ) -> ExecParams {
-    if turn_context.shell_environment_policy.use_profile {
+    let should_translate = matches!(sess.user_shell, crate::shell::Shell::PowerShell(_))
-        let command = sess
+        || turn_context.shell_environment_policy.use_profile;
+
+    if should_translate
+        && let Some(command) = sess
             .user_shell
-            .format_default_shell_invocation(params.command.clone());
+            .format_default_shell_invocation(params.command.clone())
-        if let Some(command) = command {
+    {
-            return ExecParams { command, ..params };
+        return ExecParams { command, ..params };
-        }
     }
     params
 }
@@ -2227,7 +2231,7 @@ async fn handle_container_exec_with_params(
         ),
     };
 
-    let params = maybe_run_with_user_profile(params, sess, turn_context);
+    let params = maybe_translate_shell_command(params, sess, turn_context);
     let output_result = sess
         .run_exec_with_events(
             turn_diff_tracker,

codex-rs/core/src/environment_context.rs

@@ -6,6 +6,7 @@ use crate::models::ContentItem;
 use crate::models::ResponseItem;
 use crate::protocol::AskForApproval;
 use crate::protocol::SandboxPolicy;
+use crate::shell::Shell;
 use codex_protocol::config_types::SandboxMode;
 use std::fmt::Display;
 use std::path::PathBuf;
@@ -28,6 +29,7 @@ pub(crate) struct EnvironmentContext {
     pub approval_policy: AskForApproval,
     pub sandbox_mode: SandboxMode,
     pub network_access: NetworkAccess,
+    pub shell: Shell,
 }
 
 impl EnvironmentContext {
@@ -35,6 +37,7 @@ impl EnvironmentContext {
         cwd: PathBuf,
         approval_policy: AskForApproval,
         sandbox_policy: SandboxPolicy,
+        shell: Shell,
     ) -> Self {
         Self {
             cwd,
@@ -55,6 +58,7 @@ impl EnvironmentContext {
                     }
                 }
             },
+            shell,
         }
     }
 }
@@ -69,6 +73,9 @@ impl Display for EnvironmentContext {
         writeln!(f, "Approval policy: {}", self.approval_policy)?;
         writeln!(f, "Sandbox mode: {}", self.sandbox_mode)?;
         writeln!(f, "Network access: {}", self.network_access)?;
+        if let Some(shell_name) = self.shell.name() {
+            writeln!(f, "Shell: {shell_name}")?;
+        }
         Ok(())
     }
 }

codex-rs/core/src/shell.rs

@@ -1,14 +1,24 @@
+use serde::Deserialize;
+use serde::Serialize;
 use shlex;
+use std::path::PathBuf;
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
 pub struct ZshShell {
     shell_path: String,
     zshrc_path: String,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
+pub struct PowerShellConfig {
+    exe: String, // Executable name or path, e.g. "pwsh" or "powershell.exe".
+    bash_exe_fallback: Option<PathBuf>, // In case the model generates a bash command.
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
 pub enum Shell {
     Zsh(ZshShell),
+    PowerShell(PowerShellConfig),
     Unknown,
 }
 
@@ -33,6 +43,61 @@ impl Shell {
                 }
                 Some(result)
             }
+            Shell::PowerShell(ps) => {
+                // If model generated a bash command, prefer a detected bash fallback
+                if let Some(script) = strip_bash_lc(&command) {
+                    return match &ps.bash_exe_fallback {
+                        Some(bash) => Some(vec![
+                            bash.to_string_lossy().to_string(),
+                            "-lc".to_string(),
+                            script,
+                        ]),
+
+                        // No bash fallback → run the script under PowerShell.
+                        // It will likely fail (except for some simple commands), but the error
+                        // should give a clue to the model to fix upon retry that it's running under PowerShell.
+                        None => Some(vec![
+                            ps.exe.clone(),
+                            "-NoProfile".to_string(),
+                            "-Command".to_string(),
+                            script,
+                        ]),
+                    };
+                }
+
+                // Not a bash command. If model did not generate a PowerShell command,
+                // turn it into a PowerShell command.
+                let first = command.first().map(String::as_str);
+                if first != Some(ps.exe.as_str()) {
+                    // TODO (CODEX_2900): Handle escaping newlines.
+                    if command.iter().any(|a| a.contains('\n') || a.contains('\r')) {
+                        return Some(command);
+                    }
+
+                    let joined = shlex::try_join(command.iter().map(|s| s.as_str())).ok();
+                    return joined.map(|arg| {
+                        vec![
+                            ps.exe.clone(),
+                            "-NoProfile".to_string(),
+                            "-Command".to_string(),
+                            arg,
+                        ]
+                    });
+                }
+
+                // Model generated a PowerShell command. Run it.
+                Some(command)
+            }
+            Shell::Unknown => None,
+        }
+    }
+
+    pub fn name(&self) -> Option<String> {
+        match self {
+            Shell::Zsh(zsh) => std::path::Path::new(&zsh.shell_path)
+                .file_name()
+                .map(|s| s.to_string_lossy().to_string()),
+            Shell::PowerShell(ps) => Some(ps.exe.clone()),
             Shell::Unknown => None,
         }
     }
@@ -86,11 +151,51 @@ pub async fn default_user_shell() -> Shell {
     }
 }
 
-#[cfg(not(target_os = "macos"))]
+#[cfg(all(not(target_os = "macos"), not(target_os = "windows")))]
 pub async fn default_user_shell() -> Shell {
     Shell::Unknown
 }
 
+#[cfg(target_os = "windows")]
+pub async fn default_user_shell() -> Shell {
+    use tokio::process::Command;
+
+    // Prefer PowerShell 7+ (`pwsh`) if available, otherwise fall back to Windows PowerShell.
+    let has_pwsh = Command::new("pwsh")
+        .arg("-NoLogo")
+        .arg("-NoProfile")
+        .arg("-Command")
+        .arg("$PSVersionTable.PSVersion.Major")
+        .output()
+        .await
+        .map(|o| o.status.success())
+        .unwrap_or(false);
+    let bash_exe = if Command::new("bash.exe")
+        .arg("--version")
+        .output()
+        .await
+        .ok()
+        .map(|o| o.status.success())
+        .unwrap_or(false)
+    {
+        which::which("bash.exe").ok()
+    } else {
+        None
+    };
+
+    if has_pwsh {
+        Shell::PowerShell(PowerShellConfig {
+            exe: "pwsh.exe".to_string(),
+            bash_exe_fallback: bash_exe,
+        })
+    } else {
+        Shell::PowerShell(PowerShellConfig {
+            exe: "powershell.exe".to_string(),
+            bash_exe_fallback: bash_exe,
+        })
+    }
+}
+
 #[cfg(test)]
 #[cfg(target_os = "macos")]
 mod tests {
@@ -231,3 +336,97 @@ mod tests {
         }
     }
 }
+
+#[cfg(test)]
+#[cfg(target_os = "windows")]
+mod tests_windows {
+    use super::*;
+
+    #[test]
+    fn test_format_default_shell_invocation_powershell() {
+        let cases = vec![
+            (
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "pwsh.exe".to_string(),
+                    bash_exe_fallback: None,
+                }),
+                vec!["bash", "-lc", "echo hello"],
+                vec!["pwsh.exe", "-NoProfile", "-Command", "echo hello"],
+            ),
+            (
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "powershell.exe".to_string(),
+                    bash_exe_fallback: None,
+                }),
+                vec!["bash", "-lc", "echo hello"],
+                vec!["powershell.exe", "-NoProfile", "-Command", "echo hello"],
+            ),
+            (
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "pwsh.exe".to_string(),
+                    bash_exe_fallback: Some(PathBuf::from("bash.exe")),
+                }),
+                vec!["bash", "-lc", "echo hello"],
+                vec!["bash.exe", "-lc", "echo hello"],
+            ),
+            (
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "pwsh.exe".to_string(),
+                    bash_exe_fallback: Some(PathBuf::from("bash.exe")),
+                }),
+                vec![
+                    "bash",
+                    "-lc",
+                    "apply_patch <<'EOF'\n*** Begin Patch\n*** Update File: destination_file.txt\n-original content\n+modified content\n*** End Patch\nEOF",
+                ],
+                vec![
+                    "bash.exe",
+                    "-lc",
+                    "apply_patch <<'EOF'\n*** Begin Patch\n*** Update File: destination_file.txt\n-original content\n+modified content\n*** End Patch\nEOF",
+                ],
+            ),
+            (
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "pwsh.exe".to_string(),
+                    bash_exe_fallback: Some(PathBuf::from("bash.exe")),
+                }),
+                vec!["echo", "hello"],
+                vec!["pwsh.exe", "-NoProfile", "-Command", "echo hello"],
+            ),
+            (
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "pwsh.exe".to_string(),
+                    bash_exe_fallback: Some(PathBuf::from("bash.exe")),
+                }),
+                vec!["pwsh.exe", "-NoProfile", "-Command", "echo hello"],
+                vec!["pwsh.exe", "-NoProfile", "-Command", "echo hello"],
+            ),
+            (
+                // TODO (CODEX_2900): Handle escaping newlines for powershell invocation.
+                Shell::PowerShell(PowerShellConfig {
+                    exe: "powershell.exe".to_string(),
+                    bash_exe_fallback: Some(PathBuf::from("bash.exe")),
+                }),
+                vec![
+                    "codex-mcp-server.exe",
+                    "--codex-run-as-apply-patch",
+                    "*** Begin Patch\n*** Update File: C:\\Users\\person\\destination_file.txt\n-original content\n+modified content\n*** End Patch",
+                ],
+                vec![
+                    "codex-mcp-server.exe",
+                    "--codex-run-as-apply-patch",
+                    "*** Begin Patch\n*** Update File: C:\\Users\\person\\destination_file.txt\n-original content\n+modified content\n*** End Patch",
+                ],
+            ),
+        ];
+
+        for (shell, input, expected_cmd) in cases {
+            let actual_cmd = shell
+                .format_default_shell_invocation(input.iter().map(|s| s.to_string()).collect());
+            assert_eq!(
+                actual_cmd,
+                Some(expected_cmd.iter().map(|s| s.to_string()).collect())
+            );
+        }
+    }
+}

codex-rs/core/tests/prompt_caching.rs

@@ -8,6 +8,7 @@ use codex_core::protocol::Op;
 use codex_core::protocol::SandboxPolicy;
 use codex_core::protocol_config_types::ReasoningEffort;
 use codex_core::protocol_config_types::ReasoningSummary;
+use codex_core::shell::default_user_shell;
 use codex_login::CodexAuth;
 use core_test_support::load_default_config_for_test;
 use core_test_support::load_sse_fixture_with_id;
@@ -85,9 +86,15 @@ async fn prefixes_context_and_instructions_once_and_consistently_across_requests
     let requests = server.received_requests().await.unwrap();
     assert_eq!(requests.len(), 2, "expected two POST requests");
 
+    let shell = default_user_shell().await;
+
     let expected_env_text = format!(
-        "<environment_context>\nCurrent working directory: {}\nApproval policy: on-request\nSandbox mode: read-only\nNetwork access: restricted\n</environment_context>",
+        "<environment_context>\nCurrent working directory: {}\nApproval policy: on-request\nSandbox mode: read-only\nNetwork access: restricted\n{}</environment_context>",
-        cwd.path().to_string_lossy()
+        cwd.path().to_string_lossy(),
+        match shell.name() {
+            Some(name) => format!("Shell: {name}\n"),
+            None => String::new(),
+        }
     );
     let expected_ui_text =
         "<user_instructions>\n\nbe consistent and helpful\n\n</user_instructions>";
@@ -237,9 +244,14 @@ async fn overrides_turn_context_but_keeps_cached_prefix_and_key_constant() {
     });
     // After overriding the turn context, the environment context should be emitted again
     // reflecting the new cwd, approval policy and sandbox settings.
+    let shell = default_user_shell().await;
     let expected_env_text_2 = format!(
-        "<environment_context>\nCurrent working directory: {}\nApproval policy: never\nSandbox mode: workspace-write\nNetwork access: enabled\n</environment_context>",
+        "<environment_context>\nCurrent working directory: {}\nApproval policy: never\nSandbox mode: workspace-write\nNetwork access: enabled\n{}</environment_context>",
-        new_cwd.path().to_string_lossy()
+        new_cwd.path().to_string_lossy(),
+        match shell.name() {
+            Some(name) => format!("Shell: {name}\n"),
+            None => String::new(),
+        }
     );
     let expected_env_msg_2 = serde_json::json!({
         "type": "message",