[apps] Add apps MCP path override (#20231)

Summary

- Add `[features.apps_mcp_path_override]` config with a `path` field for
overriding only the built-in apps MCP path.
- Keep existing host/base URL derivation unchanged and append the
configured path after that base.
- Regenerate the config schema with the custom feature-config case.

Test Plan

- Not run for latest revision; only `just fmt` and `just
write-config-schema` were run.
- Earlier revision: `cargo test -p codex-features`
- Earlier revision: `cargo test -p codex-mcp`

codex-rs/core/src/config/config_tests.rs

@@ -3241,8 +3241,13 @@ async fn to_mcp_config_preserves_apps_feature_from_config() -> std::io::Result<(
     .await?;
     let plugins_manager = PluginsManager::new(codex_home.path().to_path_buf());
 
+    config.apps_mcp_path_override = Some("/custom/mcp".to_string());
     let mcp_config = config.to_mcp_config(&plugins_manager).await;
     assert!(mcp_config.apps_enabled);
+    assert_eq!(
+        mcp_config.apps_mcp_path_override.as_deref(),
+        Some("/custom/mcp")
+    );
 
     let _ = config.features.disable(Feature::Apps);
     let mcp_config = config.to_mcp_config(&plugins_manager).await;
@@ -5945,6 +5950,7 @@ async fn test_precedence_fixture_with_o3_profile() -> std::io::Result<()> {
             model_verbosity: None,
             personality: Some(Personality::Pragmatic),
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
+            apps_mcp_path_override: None,
             realtime_audio: RealtimeAudioConfig::default(),
             experimental_realtime_start_instructions: None,
             experimental_realtime_ws_base_url: None,
@@ -6139,6 +6145,7 @@ async fn test_precedence_fixture_with_gpt3_profile() -> std::io::Result<()> {
         model_verbosity: None,
         personality: Some(Personality::Pragmatic),
         chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
+        apps_mcp_path_override: None,
         realtime_audio: RealtimeAudioConfig::default(),
         experimental_realtime_start_instructions: None,
         experimental_realtime_ws_base_url: None,
@@ -6287,6 +6294,7 @@ async fn test_precedence_fixture_with_zdr_profile() -> std::io::Result<()> {
         model_verbosity: None,
         personality: Some(Personality::Pragmatic),
         chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
+        apps_mcp_path_override: None,
         realtime_audio: RealtimeAudioConfig::default(),
         experimental_realtime_start_instructions: None,
         experimental_realtime_ws_base_url: None,
@@ -6420,6 +6428,7 @@ async fn test_precedence_fixture_with_gpt5_profile() -> std::io::Result<()> {
         model_verbosity: Some(Verbosity::High),
         personality: Some(Personality::Pragmatic),
         chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
+        apps_mcp_path_override: None,
         realtime_audio: RealtimeAudioConfig::default(),
         experimental_realtime_start_instructions: None,
         experimental_realtime_ws_base_url: None,
@@ -7058,6 +7067,32 @@ allow_login_shell = false
     Ok(())
 }
 
+#[tokio::test]
+async fn config_loads_apps_mcp_path_override_from_feature_config() -> std::io::Result<()> {
+    let codex_home = TempDir::new()?;
+    let toml = r#"
+model = "gpt-5.4"
+
+[features.apps_mcp_path_override]
+path = "/custom/mcp"
+"#;
+    let cfg: ConfigToml =
+        toml::from_str(toml).expect("TOML deserialization should succeed for apps MCP feature");
+
+    let config = Config::load_from_base_config_with_overrides(
+        cfg,
+        ConfigOverrides::default(),
+        codex_home.abs(),
+    )
+    .await?;
+
+    assert_eq!(
+        config.apps_mcp_path_override.as_deref(),
+        Some("/custom/mcp")
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn config_loads_mcp_oauth_callback_url_from_toml() -> std::io::Result<()> {
     let codex_home = TempDir::new()?;

codex-rs/core/src/config/mod.rs

@@ -55,6 +55,7 @@ use codex_config::types::UriBasedFileOpener;
 use codex_config::types::WindowsSandboxModeToml;
 use codex_exec_server::ExecutorFileSystem;
 use codex_exec_server::LOCAL_FS;
+use codex_features::AppsMcpPathOverrideConfigToml;
 use codex_features::Feature;
 use codex_features::FeatureConfigSource;
 use codex_features::FeatureOverrides;
@@ -647,6 +648,9 @@ pub struct Config {
     /// Base URL for requests to ChatGPT (as opposed to the OpenAI API).
     pub chatgpt_base_url: String,
 
+    /// Optional path override for the built-in apps MCP server.
+    pub apps_mcp_path_override: Option<String>,
+
     /// Machine-local realtime audio device preferences used by realtime voice.
     pub realtime_audio: RealtimeAudioConfig,
 
@@ -977,6 +981,7 @@ impl Config {
 
         McpConfig {
             chatgpt_base_url: self.chatgpt_base_url.clone(),
+            apps_mcp_path_override: self.apps_mcp_path_override.clone(),
             codex_home: self.codex_home.to_path_buf(),
             mcp_oauth_credentials_store_mode: self.mcp_oauth_credentials_store_mode,
             mcp_oauth_callback_port: self.mcp_oauth_callback_port,
@@ -1786,6 +1791,15 @@ fn multi_agent_v2_toml_config(features: Option<&FeaturesToml>) -> Option<&MultiA
     }
 }
 
+fn apps_mcp_path_override_toml_config(
+    features: Option<&FeaturesToml>,
+) -> Option<&AppsMcpPathOverrideConfigToml> {
+    match features?.apps_mcp_path_override.as_ref()? {
+        FeatureToml::Enabled(_) => None,
+        FeatureToml::Config(config) => Some(config),
+    }
+}
+
 pub(crate) fn resolve_web_search_mode_for_turn(
     web_search_mode: &Constrained<WebSearchMode>,
     permission_profile: &PermissionProfile,
@@ -2237,6 +2251,16 @@ impl Config {
             .unwrap_or(WebSearchMode::Cached);
         let web_search_config = resolve_web_search_config(&cfg, &config_profile);
         let multi_agent_v2 = resolve_multi_agent_v2_config(&cfg, &config_profile);
+        let apps_mcp_path_override = if features.enabled(Feature::AppsMcpPathOverride) {
+            let base = apps_mcp_path_override_toml_config(cfg.features.as_ref());
+            let profile = apps_mcp_path_override_toml_config(config_profile.features.as_ref());
+            profile
+                .and_then(|config| config.path.as_ref())
+                .or_else(|| base.and_then(|config| config.path.as_ref()))
+                .cloned()
+        } else {
+            None
+        };
         let terminal_resize_reflow = resolve_terminal_resize_reflow_config(&cfg);
 
         let agent_roles =
@@ -2738,6 +2762,7 @@ impl Config {
                 .chatgpt_base_url
                 .or(cfg.chatgpt_base_url)
                 .unwrap_or("https://chatgpt.com/backend-api/".to_string()),
+            apps_mcp_path_override,
             realtime_audio: cfg
                 .audio
                 .map_or_else(RealtimeAudioConfig::default, |audio| RealtimeAudioConfig {