fix(mcp): default Apps product SKU to codex (#31803)

## Motivation

Host-owned Apps MCP requests currently omit `X-OpenAI-Product-Sku`
unless `apps_mcp_product_sku` is explicitly configured. Codex requests
should identify themselves with the `codex` product SKU by default.

## Changes

- Default `X-OpenAI-Product-Sku` to `codex`.
- Preserve explicitly configured SKU values.
- Add coverage for both default and configured behavior.

## Impact

Codex Apps MCP requests now include the expected product identity
without requiring local configuration. Existing explicit SKU overrides
are unchanged.

## Testing

- `just test -p codex-mcp
codex_apps_server_config_sets_product_sku_header`
- `just fix -p codex-mcp`
- `just fmt`

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

@@ -51,6 +51,7 @@ use crate::runtime::McpRuntimeContext;
 use crate::server::EffectiveMcpServer;
 
 pub const CODEX_APPS_MCP_SERVER_NAME: &str = "codex_apps";
+const DEFAULT_CODEX_APPS_MCP_PRODUCT_SKU: &str = "codex";
 const MCP_TOOL_NAME_PREFIX: &str = "mcp";
 const MCP_TOOL_NAME_DELIMITER: &str = "__";
 const CODEX_CONNECTORS_TOKEN_ENV_VAR: &str = "CODEX_CONNECTORS_TOKEN";
@@ -523,9 +524,11 @@ fn mcp_server_config_for_url(
     apps_mcp_product_sku: Option<&str>,
     auth_mode: McpServerAuth,
 ) -> McpServerConfig {
-    let http_headers = apps_mcp_product_sku.map(|product_sku| {
+    let product_sku = apps_mcp_product_sku.unwrap_or(DEFAULT_CODEX_APPS_MCP_PRODUCT_SKU);
-        HashMap::from([("X-OpenAI-Product-Sku".to_string(), product_sku.to_string())])
+    let http_headers = Some(HashMap::from([(
-    });
+        "X-OpenAI-Product-Sku".to_string(),
+        product_sku.to_string(),
+    )]));
 
     McpServerConfig {
         transport: McpServerTransportConfig::StreamableHttp {

codex-rs/codex-mcp/src/mcp/mod_tests.rs

@@ -263,25 +263,27 @@ fn codex_apps_server_config_uses_legacy_codex_apps_path() {
 }
 
 #[test]
-fn codex_apps_server_config_forwards_configured_product_sku_header() {
+fn codex_apps_server_config_sets_product_sku_header() {
-    let config = codex_apps_mcp_server_config("https://chatgpt.com", Some("tpp"));
+    for (configured_product_sku, expected_product_sku) in [(None, "codex"), (Some("tpp"), "tpp")] {
+        let config = codex_apps_mcp_server_config("https://chatgpt.com", configured_product_sku);
 
-    match &config.transport {
+        match &config.transport {
-        McpServerTransportConfig::StreamableHttp {
+            McpServerTransportConfig::StreamableHttp {
-            http_headers,
-            env_http_headers,
-            ..
-        } => {
-            assert_eq!(
                 http_headers,
-                &Some(HashMap::from([(
+                env_http_headers,
-                    "X-OpenAI-Product-Sku".to_string(),
+                ..
-                    "tpp".to_string(),
+            } => {
-                )]))
+                assert_eq!(
-            );
+                    http_headers,
-            assert!(env_http_headers.is_none());
+                    &Some(HashMap::from([(
+                        "X-OpenAI-Product-Sku".to_string(),
+                        expected_product_sku.to_string(),
+                    )]))
+                );
+                assert!(env_http_headers.is_none());
+            }
+            other => panic!("expected streamable http transport, got {other:?}"),
         }
-        other => panic!("expected streamable http transport, got {other:?}"),
     }
 }