Validate CODEX_HOME before resolving (#10249)

Summary
- require `CODEX_HOME` to point to an existing directory before
canonicalizing and surface clear errors otherwise
- share the same helper logic in both `core` and `rmcp-client` and add
unit tests that cover missing, non-directory, valid, and default paths

This addresses #9222

codex-rs/rmcp-client/Cargo.toml

@@ -15,7 +15,7 @@ axum = { workspace = true, default-features = false, features = [
 ] }
 codex-keyring-store = { workspace = true }
 codex-protocol = { workspace = true }
-dirs = { workspace = true }
+codex-utils-home-dir = { workspace = true }
 futures = { workspace = true, default-features = false, features = ["std"] }
 keyring = { workspace = true, features = ["crypto-rust"] }
 mcp-types = { path = "../mcp-types" }

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

@@ -1,33 +0,0 @@
-use dirs::home_dir;
-use std::path::PathBuf;
-
-/// This was copied from codex-core but codex-core depends on this crate.
-/// TODO: move this to a shared crate lower in the dependency tree.
-///
-///
-/// Returns the path to the Codex configuration directory, which can be
-/// specified by the `CODEX_HOME` environment variable. If not set, defaults to
-/// `~/.codex`.
-///
-/// - If `CODEX_HOME` is set, the value will be canonicalized and this
-///   function will Err if the path does not exist.
-/// - If `CODEX_HOME` is not set, this function does not verify that the
-///   directory exists.
-pub(crate) fn find_codex_home() -> std::io::Result<PathBuf> {
-    // Honor the `CODEX_HOME` environment variable when it is set to allow users
-    // (and tests) to override the default location.
-    if let Ok(val) = std::env::var("CODEX_HOME")
-        && !val.is_empty()
-    {
-        return PathBuf::from(val).canonicalize();
-    }
-
-    let mut p = home_dir().ok_or_else(|| {
-        std::io::Error::new(
-            std::io::ErrorKind::NotFound,
-            "Could not find home directory",
-        )
-    })?;
-    p.push(".codex");
-    Ok(p)
-}

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

@@ -1,5 +1,4 @@
 mod auth_status;
-mod find_codex_home;
 mod logging_client_handler;
 mod oauth;
 mod perform_oauth_login;

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

@@ -48,7 +48,7 @@ use codex_keyring_store::KeyringStore;
 use rmcp::transport::auth::AuthorizationManager;
 use tokio::sync::Mutex;
 
-use crate::find_codex_home::find_codex_home;
+use codex_utils_home_dir::find_codex_home;
 
 const KEYRING_SERVICE: &str = "Codex MCP Credentials";
 const REFRESH_SKEW_MILLIS: u64 = 30_000;