[codex] Use background task auth for additional backend calls (#18260)

## Summary

Splits the larger PR4.1 background task auth rollout by moving
additional backend/control-plane call sites into this downstream PR.

This PR keeps callers on the same design as PR4.1: most code asks
`AuthManager` for the default ChatGPT backend authorization header, and
`AuthManager` decides bearer vs background AgentAssertion internally.
Task-pinned inference auth remains separate because it needs the
thread's registered task id.

## Stack

- PR1: https://github.com/openai/codex/pull/17385 - add
`features.use_agent_identity`
- PR2: https://github.com/openai/codex/pull/17386 - register agent
identities when enabled
- PR3: https://github.com/openai/codex/pull/17387 - register agent tasks
when enabled
- PR3.1: https://github.com/openai/codex/pull/17978 - persist and
prewarm registered tasks per thread
- PR4: https://github.com/openai/codex/pull/17980 - use task-scoped
`AgentAssertion` for downstream calls
- PR4.1: https://github.com/openai/codex/pull/18094 - introduce
AuthManager-owned background/control-plane `AgentAssertion` auth
- PR4.2: this PR - use background task auth for additional
backend/control-plane calls

## What Changed

- pass full authorization header values through backend-client and
cloud-tasks-client call paths where needed
- move ChatGPT client, cloud requirements, cloud tasks, thread-manager,
and models-manager background auth usage into this downstream slice
- make app-server remote control enrollment/websocket auth ask
`AuthManager` for the local backend authorization header instead of
threading a background auth mode through transport options
- keep the same feature-gated bearer fallback behavior from PR4.1

## Validation

- `just fmt`
- `cargo check -p codex-core -p codex-login -p codex-analytics -p
codex-app-server -p codex-cloud-requirements -p codex-cloud-tasks -p
codex-models-manager -p codex-chatgpt -p codex-model-provider -p
codex-mcp -p codex-core-skills`
- `cargo test -p codex-login agent_identity`
- `cargo test -p codex-model-provider bearer_auth_provider`
- `cargo test -p codex-core agent_assertion`
- `cargo test -p codex-app-server remote_control`
- `cargo test -p codex-cloud-requirements fetch_cloud_requirements`
- `cargo test -p codex-models-manager manager::tests`
- `cargo test -p codex-chatgpt`
- `cargo test -p codex-cloud-tasks`
- `just fix -p codex-core -p codex-login -p codex-analytics -p
codex-app-server -p codex-cloud-requirements -p codex-cloud-tasks -p
codex-models-manager -p codex-chatgpt -p codex-model-provider -p
codex-mcp -p codex-core-skills`
- `just fix -p codex-app-server`
- `git diff --check`

codex-rs/cloud-tasks/src/lib.rs

@@ -68,43 +68,45 @@ async fn init_backend(user_agent_suffix: &str) -> anyhow::Result<BackendContext>
     };
     append_error_log(format!("startup: base_url={base_url} path_style={style}"));
 
-    let auth_manager = util::load_auth_manager().await;
-    let auth = match auth_manager.as_ref() {
-        Some(manager) => manager.auth().await,
-        None => None,
+    let Some(auth_manager) = util::load_auth_manager(Some(base_url.clone())).await else {
+        eprintln!(
+            "Not signed in. Please run 'codex login' to sign in with ChatGPT, then re-run 'codex cloud'."
+        );
+        std::process::exit(1);
     };
-    let auth = match auth {
-        Some(auth) => auth,
-        None => {
-            eprintln!(
-                "Not signed in. Please run 'codex login' to sign in with ChatGPT, then re-run 'codex cloud'."
-            );
-            std::process::exit(1);
-        }
+    let Some(auth) = auth_manager.auth().await else {
+        eprintln!(
+            "Not signed in. Please run 'codex login' to sign in with ChatGPT, then re-run 'codex cloud'."
+        );
+        std::process::exit(1);
     };
 
     if let Some(acc) = auth.get_account_id() {
         append_error_log(format!("auth: mode=ChatGPT account_id={acc}"));
     }
 
-    let token = match auth.get_token() {
-        Ok(t) if !t.is_empty() => t,
-        _ => {
-            eprintln!(
-                "Not signed in. Please run 'codex login' to sign in with ChatGPT, then re-run 'codex cloud'."
-            );
-            std::process::exit(1);
-        }
+    let authorization_header_value = auth_manager
+        .chatgpt_authorization_header_for_auth(&auth)
+        .await;
+    let Some(authorization_header_value) = authorization_header_value else {
+        eprintln!(
+            "Not signed in. Please run 'codex login' to sign in with ChatGPT, then re-run 'codex cloud'."
+        );
+        std::process::exit(1);
     };
 
-    http = http.with_bearer_token(token.clone());
-    if let Some(acc) = auth
-        .get_account_id()
-        .or_else(|| util::extract_chatgpt_account_id(&token))
-    {
+    http = http.with_authorization_header_value(authorization_header_value);
+    if let Some(acc) = auth.get_account_id().or_else(|| {
+        auth.get_token()
+            .ok()
+            .and_then(|token| util::extract_chatgpt_account_id(&token))
+    }) {
         append_error_log(format!("auth: set ChatGPT-Account-Id header: {acc}"));
         http = http.with_chatgpt_account_id(acc);
     }
+    if auth.is_fedramp_account() {
+        http = http.with_fedramp_routing_header();
+    }
 
     Ok(BackendContext {
         backend: Arc::new(http),