[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/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 {