Reduce response serialization and rollout scan overhead (#36006)

## What changed

- Keep `ClientResponsePayload` typed through the app-server outgoing queue and serialize it at the transport boundary, avoiding an intermediate `serde_json::Value` while preserving the JSON-RPC wire shape.
- Return a JSON-RPC internal error when a response cannot be serialized, including over remote control, and skip unserializable analytics responses.
- Scan reverse JSONL input a chunk at a time with a larger buffer instead of processing each byte individually.

## Testing

- Cover typed response serialization and serialization failures for direct and remote-control transports.
- Cover filtering unserializable responses from analytics.

GitOrigin-RevId: cc4fd7a43461a273315bb95261bd1ae3ff65fbf7

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

@@ -5,18 +5,13 @@ use pretty_assertions::assert_eq;
 use serde_json::json;
 
 #[test]
-fn client_response_payload_returns_jsonrpc_parts_and_client_response() -> Result<()> {
-    let (request_id, result, payload) =
-        ClientResponsePayload::ThreadArchive(v2::ThreadArchiveResponse {})
-            .into_jsonrpc_parts_and_payload(RequestId::Integer(7))?;
-
-    assert_eq!(request_id, RequestId::Integer(7));
-    assert_eq!(result, json!({}));
-
+fn client_response_payload_serializes_without_an_intermediate_json_value() -> Result<()> {
+    let payload = ClientResponsePayload::ThreadArchive(v2::ThreadArchiveResponse {});
+    assert_eq!(serde_json::to_string(&payload)?, "{}");
     let Some(ClientResponse::ThreadArchive {
         request_id,
         response: _,
-    }) = payload.and_then(|payload| payload.into_client_response(RequestId::Integer(7)))
+    }) = payload.into_client_response(RequestId::Integer(7))
     else {
         panic!("expected thread/archive client response");
     };
@@ -26,19 +21,19 @@ fn client_response_payload_returns_jsonrpc_parts_and_client_response() -> Result
 
 #[test]
 fn interrupt_conversation_payload_stays_jsonrpc_only() -> Result<()> {
-    let (request_id, result, payload) =
-        ClientResponsePayload::InterruptConversation(v1::InterruptConversationResponse {
-            abort_reason: TurnAbortReason::Interrupted,
-        })
-        .into_jsonrpc_parts_and_payload(RequestId::Integer(8))?;
-
-    assert_eq!(request_id, RequestId::Integer(8));
+    let payload = ClientResponsePayload::InterruptConversation(v1::InterruptConversationResponse {
+        abort_reason: TurnAbortReason::Interrupted,
+    });
     assert_eq!(
-        result,
+        serde_json::to_value(&payload)?,
         json!({
             "abortReason": "interrupted",
         })
     );
-    assert!(payload.is_none());
+    assert!(
+        payload
+            .into_client_response(RequestId::Integer(8))
+            .is_none()
+    );
     Ok(())
 }