mcp: accept foreign absolute cwd for remote stdio (#29493)

## Why

Remote stdio MCP servers can run in an environment whose path convention
differs from the Codex host. A Windows cwd such as
`C:\Users\openai\share` is absolute for the executor but was rejected by
a POSIX orchestrator.

Built on #29501, now merged, which only clarifies the host-native
`PathUri` constructor name.

## What changed

- Deserialize MCP cwd values as `LegacyAppPathString` so config does not
apply host path rules.
- Interpret that spelling as host-native for local launches and convert
it to `PathUri` at executor launch.
- Skip host filesystem and command resolution checks for remote stdio in
`codex doctor`.
- Add host-independent config and executor-boundary coverage using the
foreign path convention for each test platform.

## Validation

- `just test -p codex-utils-path-uri -p codex-config -p codex-mcp -p
codex-rmcp-client` (408 passed)
- `just test -p codex-cli -p codex-rmcp-client` (372 passed)
- `cargo check --workspace --tests`
- `just test` (11,311 passed; 43 unrelated environment/timing failures)
- `just fix -p codex-cli -p codex-config -p codex-core -p codex-mcp -p
codex-mcp-extension -p codex-rmcp-client -p codex-tui`

codex-rs/config/src/mcp_edit.rs

@@ -146,7 +146,7 @@ fn serialize_mcp_server(config: &McpServerConfig) -> TomlItem {
                 entry["env_vars"] = array_from_env_vars(env_vars);
             }
             if let Some(cwd) = cwd {
-                entry["cwd"] = value(cwd.to_string_lossy().to_string());
+                entry["cwd"] = value(cwd.as_str());
             }
         }
         McpServerTransportConfig::StreamableHttp {

codex-rs/config/src/mcp_types.rs

@@ -2,9 +2,9 @@
 
 use std::collections::HashMap;
 use std::fmt;
-use std::path::PathBuf;
 use std::time::Duration;
 
+use codex_utils_path_uri::LegacyAppPathString;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde::Deserializer;
@@ -224,7 +224,7 @@ pub struct RawMcpServerConfig {
     #[serde(default)]
     pub env_vars: Option<Vec<McpServerEnvVar>>,
     #[serde(default)]
-    pub cwd: Option<PathBuf>,
+    pub cwd: Option<LegacyAppPathString>,
     pub http_headers: Option<HashMap<String, String>>,
     #[serde(default)]
     pub env_http_headers: Option<HashMap<String, String>>,
@@ -358,7 +358,6 @@ impl TryFrom<RawMcpServerConfig> for McpServerConfig {
 
         let environment_id =
             environment_id.unwrap_or_else(|| DEFAULT_MCP_SERVER_ENVIRONMENT_ID.to_string());
-        validate_remote_stdio_cwd(&transport, &environment_id)?;
 
         Ok(Self {
             transport,
@@ -395,30 +394,6 @@ const fn default_enabled() -> bool {
     true
 }
 
-fn validate_remote_stdio_cwd(
-    transport: &McpServerTransportConfig,
-    environment_id: &str,
-) -> Result<(), String> {
-    if environment_id == DEFAULT_MCP_SERVER_ENVIRONMENT_ID {
-        return Ok(());
-    }
-    let McpServerTransportConfig::Stdio { cwd, .. } = transport else {
-        return Ok(());
-    };
-    let Some(cwd) = cwd else {
-        return Err(format!(
-            "remote stdio MCP servers require an absolute cwd when environment_id is `{environment_id}`"
-        ));
-    };
-    if cwd.is_absolute() {
-        return Ok(());
-    }
-    Err(format!(
-        "remote stdio MCP servers require an absolute cwd when environment_id is `{environment_id}`, got `{}`",
-        cwd.display()
-    ))
-}
-
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema)]
 #[serde(untagged, deny_unknown_fields, rename_all = "snake_case")]
 pub enum McpServerTransportConfig {
@@ -432,7 +407,7 @@ pub enum McpServerTransportConfig {
         #[serde(default, skip_serializing_if = "Vec::is_empty")]
         env_vars: Vec<McpServerEnvVar>,
         #[serde(default, skip_serializing_if = "Option::is_none")]
-        cwd: Option<PathBuf>,
+        cwd: Option<LegacyAppPathString>,
     },
     /// https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#streamable-http
     StreamableHttp {

codex-rs/config/src/mcp_types_tests.rs

@@ -1,7 +1,8 @@
 use super::*;
+use codex_utils_path_uri::LegacyAppPathString;
 use pretty_assertions::assert_eq;
 use std::collections::HashMap;
-use std::path::PathBuf;
+use std::path::Path;
 
 #[test]
 fn deserialize_stdio_command_server_config() {
@@ -52,38 +53,12 @@ fn deserialize_stdio_command_server_config_with_args() {
 }
 
 #[test]
-fn deserialize_remote_stdio_server_requires_absolute_cwd() {
-    let missing_cwd = toml::from_str::<McpServerConfig>(
-        r#"
-            command = "echo"
-            environment_id = "remote"
-        "#,
-    )
-    .expect_err("remote stdio MCP should require cwd");
-    assert!(
-        missing_cwd
-            .to_string()
-            .contains("remote stdio MCP servers require an absolute cwd"),
-        "unexpected error: {missing_cwd}"
-    );
-
-    let relative_cwd = toml::from_str::<McpServerConfig>(
-        r#"
-            command = "echo"
-            environment_id = "remote"
-            cwd = "relative"
-        "#,
-    )
-    .expect_err("remote stdio MCP should require absolute cwd");
-    assert!(
-        relative_cwd.to_string().contains("got `relative`"),
-        "unexpected error: {relative_cwd}"
-    );
-}
-
-#[test]
-fn deserialize_remote_stdio_server_accepts_absolute_cwd() {
-    let cwd = std::env::temp_dir();
+fn deserialize_remote_stdio_server_accepts_foreign_absolute_cwd() {
+    #[cfg(not(windows))]
+    let cwd = r"C:\Users\openai\share";
+    #[cfg(windows)]
+    let cwd = "/home/openai/share";
+    let expected_cwd = LegacyAppPathString::from_path(Path::new(cwd));
     let cfg: McpServerConfig = match toml::from_str(&format!(
         r#"
             command = "echo"
@@ -102,7 +77,7 @@ fn deserialize_remote_stdio_server_accepts_absolute_cwd() {
             args: vec![],
             env: None,
             env_vars: Vec::new(),
-            cwd: Some(cwd),
+            cwd: Some(expected_cwd),
         }
     );
 }
@@ -223,7 +198,7 @@ fn deserialize_stdio_command_server_config_with_cwd() {
             args: vec![],
             env: None,
             env_vars: Vec::new(),
-            cwd: Some(PathBuf::from("/tmp")),
+            cwd: Some(LegacyAppPathString::from_path(Path::new("/tmp"))),
         }
     );
 }