[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/codex-mcp/src/mcp/mod.rs

@@ -93,6 +93,8 @@ pub fn mcp_permission_prompt_is_auto_approved(
 pub struct McpConfig {
     /// Base URL for ChatGPT-hosted app MCP servers, copied from the root config.
     pub chatgpt_base_url: String,
+    /// Optional path override for the built-in apps MCP server.
+    pub apps_mcp_path_override: Option<String>,
     /// Codex home directory used for MCP OAuth state and app-tool cache files.
     pub codex_home: PathBuf,
     /// Preferred credential store for MCP OAuth tokens.
@@ -333,7 +335,10 @@ pub async fn collect_mcp_snapshot_from_manager(
 }
 
 pub(crate) fn codex_apps_mcp_url(config: &McpConfig) -> String {
-    codex_apps_mcp_url_for_base_url(&config.chatgpt_base_url)
+    codex_apps_mcp_url_for_base_url(
+        &config.chatgpt_base_url,
+        config.apps_mcp_path_override.as_deref(),
+    )
 }
 
 /// The Responses API requires tool names to match `^[a-zA-Z0-9_-]+$`.
@@ -376,15 +381,19 @@ fn normalize_codex_apps_base_url(base_url: &str) -> String {
     base_url
 }
 
-fn codex_apps_mcp_url_for_base_url(base_url: &str) -> String {
+fn codex_apps_mcp_url_for_base_url(base_url: &str, apps_mcp_path_override: Option<&str>) -> String {
     let base_url = normalize_codex_apps_base_url(base_url);
-    if base_url.contains("/backend-api") {
-        format!("{base_url}/wham/apps")
+    let (base_url, default_path) = if base_url.contains("/backend-api") {
+        (base_url, "wham/apps")
     } else if base_url.contains("/api/codex") {
-        format!("{base_url}/apps")
+        (base_url, "apps")
     } else {
-        format!("{base_url}/api/codex/apps")
-    }
+        (format!("{base_url}/api/codex"), "apps")
+    };
+    let path = apps_mcp_path_override
+        .unwrap_or(default_path)
+        .trim_start_matches('/');
+    format!("{base_url}/{path}")
 }
 
 fn codex_apps_mcp_server_config(config: &McpConfig) -> McpServerConfig {