feat(app-server): support external auth mode (#10012)

This enables a new use case where `codex app-server` is embedded into a
parent application that will directly own the user's ChatGPT auth
lifecycle, which means it owns the user’s auth tokens and refreshes it
when necessary. The parent application would just want a way to pass in
the auth tokens for codex to use directly.

The idea is that we are introducing a new "auth mode" currently only
exposed via app server: **`chatgptAuthTokens`** which consist of the
`id_token` (stores account metadata) and `access_token` (the bearer
token used directly for backend API calls). These auth tokens are only
stored in-memory. This new mode is in addition to the existing `apiKey`
and `chatgpt` auth modes.

This PR reuses the shape of our existing app-server account APIs as much
as possible:
- Update `account/login/start` with a new `chatgptAuthTokens` variant,
which will allow the client to pass in the tokens and have codex
app-server use them directly. Upon success, the server emits
`account/login/completed` and `account/updated` notifications.
- A new server->client request called
`account/chatgptAuthTokens/refresh` which the server can use whenever
the access token previously passed in has expired and it needs a new one
from the parent application.

I leveraged the core 401 retry loop which typically triggers auth token
refreshes automatically, but made it pluggable:
- **chatgpt** mode refreshes internally, as usual.
- **chatgptAuthTokens** mode calls the client via
`account/chatgptAuthTokens/refresh`, the client responds with updated
tokens, codex updates its in-memory auth, then retries. This RPC has a
10s timeout and handles JSON-RPC errors from the client.

Also some additional things:
- chatgpt logins are blocked while external auth is active (have to log
out first. typically clients will pick one OR the other, not support
both)
- `account/logout` clears external auth in memory
- Ensures that if `forced_chatgpt_workspace_id` is set via the user's
config, we respect it in both:
- `account/login/start` with `chatgptAuthTokens` (returns a JSON-RPC
error back to the client)
- `account/chatgptAuthTokens/refresh` (fails the turn, and on next
request app-server will send another `account/chatgptAuthTokens/refresh`
request to the client).

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -28,6 +28,11 @@ impl GitSha {
 pub enum AuthMode {
     ApiKey,
     ChatGPT,
+    /// [UNSTABLE] FOR OPENAI INTERNAL USE ONLY - DO NOT USE.
+    #[serde(rename = "chatgptAuthTokens")]
+    #[ts(rename = "chatgptAuthTokens")]
+    #[strum(serialize = "chatgptAuthTokens")]
+    ChatgptAuthTokens,
 }
 
 /// Generates an `enum ClientRequest` where each variant is a request that the
@@ -534,6 +539,11 @@ server_request_definitions! {
         response: v2::DynamicToolCallResponse,
     },
 
+    ChatgptAuthTokensRefresh => "account/chatgptAuthTokens/refresh" {
+        params: v2::ChatgptAuthTokensRefreshParams,
+        response: v2::ChatgptAuthTokensRefreshResponse,
+    },
+
     /// DEPRECATED APIs below
     /// Request to approve a patch.
     /// This request is used for Turns started via the legacy APIs (i.e. SendUserTurn, SendUserMessage).
@@ -753,6 +763,29 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn serialize_chatgpt_auth_tokens_refresh_request() -> Result<()> {
+        let request = ServerRequest::ChatgptAuthTokensRefresh {
+            request_id: RequestId::Integer(8),
+            params: v2::ChatgptAuthTokensRefreshParams {
+                reason: v2::ChatgptAuthTokensRefreshReason::Unauthorized,
+                previous_account_id: Some("org-123".to_string()),
+            },
+        };
+        assert_eq!(
+            json!({
+                "method": "account/chatgptAuthTokens/refresh",
+                "id": 8,
+                "params": {
+                    "reason": "unauthorized",
+                    "previousAccountId": "org-123"
+                }
+            }),
+            serde_json::to_value(&request)?,
+        );
+        Ok(())
+    }
+
     #[test]
     fn serialize_get_account_rate_limits() -> Result<()> {
         let request = ClientRequest::GetAccountRateLimits {
@@ -842,10 +875,34 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn serialize_account_login_chatgpt_auth_tokens() -> Result<()> {
+        let request = ClientRequest::LoginAccount {
+            request_id: RequestId::Integer(5),
+            params: v2::LoginAccountParams::ChatgptAuthTokens {
+                access_token: "access-token".to_string(),
+                id_token: "id-token".to_string(),
+            },
+        };
+        assert_eq!(
+            json!({
+                "method": "account/login/start",
+                "id": 5,
+                "params": {
+                    "type": "chatgptAuthTokens",
+                    "accessToken": "access-token",
+                    "idToken": "id-token"
+                }
+            }),
+            serde_json::to_value(&request)?,
+        );
+        Ok(())
+    }
+
     #[test]
     fn serialize_get_account() -> Result<()> {
         let request = ClientRequest::GetAccount {
-            request_id: RequestId::Integer(5),
+            request_id: RequestId::Integer(6),
             params: v2::GetAccountParams {
                 refresh_token: false,
             },
@@ -853,7 +910,7 @@ mod tests {
         assert_eq!(
             json!({
                 "method": "account/read",
-                "id": 5,
+                "id": 6,
                 "params": {
                     "refreshToken": false
                 }