inline hostname resolution for remote sandbox config (#19739)

# Why

Requirements support host-specific
`remote_sandbox_config.hostname_patterns`, but config loading previously
resolved and passed the system hostname through every config-loading
path even when no requirements layer used `remote_sandbox_config`. On
machines where hostname lookup is slow, startup and app-server config
reads paid for a feature that was not active.

We only need the hostname when a requirements layer actually declares
`remote_sandbox_config`, so this moves hostname resolution to the single
requirements merge point and keeps all other config callers unaware of
hostname matching.

# What

- Removed the eager `host_name` plumbing from
`load_config_layers_state`, `load_requirements_toml`, `ConfigBuilder`,
app-server `ConfigManager`, network proxy loading, and related call
sites.
- Resolve the hostname inside
`merge_requirements_with_remote_sandbox_config` only when the incoming
requirements contain `remote_sandbox_config`.

codex-rs/app-server/src/config_manager.rs

@@ -33,7 +33,6 @@ pub(crate) struct ConfigManager {
     cloud_requirements: Arc<RwLock<CloudRequirementsLoader>>,
     arg0_paths: Arg0DispatchPaths,
     thread_config_loader: Arc<RwLock<Arc<dyn ThreadConfigLoader>>>,
-    host_name: Option<String>,
 }
 
 impl ConfigManager {
@@ -44,27 +43,6 @@ impl ConfigManager {
         cloud_requirements: CloudRequirementsLoader,
         arg0_paths: Arg0DispatchPaths,
         thread_config_loader: Arc<dyn ThreadConfigLoader>,
-    ) -> Self {
-        Self::new_with_host_name(
-            codex_home,
-            cli_overrides,
-            loader_overrides,
-            cloud_requirements,
-            arg0_paths,
-            thread_config_loader,
-            codex_config::host_name(),
-        )
-    }
-
-    #[allow(clippy::too_many_arguments)]
-    fn new_with_host_name(
-        codex_home: PathBuf,
-        cli_overrides: Vec<(String, TomlValue)>,
-        loader_overrides: LoaderOverrides,
-        cloud_requirements: CloudRequirementsLoader,
-        arg0_paths: Arg0DispatchPaths,
-        thread_config_loader: Arc<dyn ThreadConfigLoader>,
-        host_name: Option<String>,
     ) -> Self {
         Self {
             codex_home,
@@ -74,7 +52,6 @@ impl ConfigManager {
             cloud_requirements: Arc::new(RwLock::new(cloud_requirements)),
             arg0_paths,
             thread_config_loader: Arc::new(RwLock::new(thread_config_loader)),
-            host_name,
         }
     }
 
@@ -229,7 +206,6 @@ impl ConfigManager {
             .fallback_cwd(fallback_cwd)
             .cloud_requirements(self.current_cloud_requirements())
             .thread_config_loader(self.current_thread_config_loader())
-            .host_name(self.host_name.clone())
             .build()
             .await?;
         self.apply_runtime_feature_enablement(&mut config);
@@ -257,7 +233,6 @@ impl ConfigManager {
             self.loader_overrides.clone(),
             self.current_cloud_requirements(),
             thread_config_loader.as_ref(),
-            self.host_name.as_deref(),
         )
         .await
     }
@@ -285,16 +260,14 @@ impl ConfigManager {
         cli_overrides: Vec<(String, TomlValue)>,
         loader_overrides: LoaderOverrides,
         cloud_requirements: CloudRequirementsLoader,
-        host_name: Option<String>,
     ) -> Self {
-        Self::new_with_host_name(
+        Self::new(
             codex_home,
             cli_overrides,
             loader_overrides,
             cloud_requirements,
             Arg0DispatchPaths::default(),
             Arc::new(codex_config::NoopThreadConfigLoader),
-            host_name,
         )
     }
 
@@ -305,7 +278,6 @@ impl ConfigManager {
             Vec::new(),
             LoaderOverrides::without_managed_config_for_tests(),
             CloudRequirementsLoader::default(),
-            /*host_name*/ None,
         )
     }
 }

codex-rs/app-server/src/config_manager_service_tests.rs

@@ -226,7 +226,6 @@ async fn read_includes_origins_and_layers() {
         vec![],
         LoaderOverrides::with_managed_config_path_for_tests(managed_path.clone()),
         CloudRequirementsLoader::default(),
-        /*host_name*/ None,
     );
 
     let response = service
@@ -305,7 +304,6 @@ writable_roots = ["~/code"]
         vec![],
         loader_overrides,
         CloudRequirementsLoader::default(),
-        /*host_name*/ None,
     );
 
     let response = service
@@ -346,7 +344,6 @@ async fn write_value_reports_override() {
         vec![],
         LoaderOverrides::with_managed_config_path_for_tests(managed_path.clone()),
         CloudRequirementsLoader::default(),
-        /*host_name*/ None,
     );
 
     let result = service
@@ -446,7 +443,6 @@ async fn invalid_user_value_rejected_even_if_overridden_by_managed() {
         vec![],
         LoaderOverrides::with_managed_config_path_for_tests(managed_path.clone()),
         CloudRequirementsLoader::default(),
-        /*host_name*/ None,
     );
 
     let error = service
@@ -514,7 +510,6 @@ async fn write_value_rejects_feature_requirement_conflict() {
                 ..Default::default()
             }))
         }),
-        /*host_name*/ None,
     );
 
     let error = service
@@ -561,7 +556,6 @@ async fn write_value_rejects_profile_feature_requirement_conflict() {
                 ..Default::default()
             }))
         }),
-        /*host_name*/ None,
     );
 
     let error = service
@@ -612,7 +606,6 @@ async fn read_reports_managed_overrides_user_and_session_flags() {
         cli_overrides,
         LoaderOverrides::with_managed_config_path_for_tests(managed_path.clone()),
         CloudRequirementsLoader::default(),
-        /*host_name*/ None,
     );
 
     let response = service
@@ -666,7 +659,6 @@ async fn write_value_reports_managed_override() {
         vec![],
         LoaderOverrides::with_managed_config_path_for_tests(managed_path.clone()),
         CloudRequirementsLoader::default(),
-        /*host_name*/ None,
     );
 
     let result = service