Require prefixes for outbound response item IDs (#32312)

## What changed

- Add a `ResponseItemId` type that generates item-specific prefixes with UUIDv7 suffixes and use it across response items.
- Keep deserialization permissive for legacy histories, but omit empty or unprefixed item IDs from HTTP and WebSocket requests.
- Export the new type in the generated TypeScript protocol schema.

## Testing

- Cover prefixed ID generation, legacy deserialization, prefix recognition, and outbound request filtering.

GitOrigin-RevId: 0209fe430c826d0ae88bc4648652c4ebf390c4a4

codex-rs/codex-api/src/endpoint/responses_websocket.rs

@@ -892,6 +892,7 @@ fn serialize_websocket_request(request: &ResponsesWsRequest) -> Result<String, A
 mod tests {
     use super::*;
     use crate::common::ResponseCreateWsRequest;
+    use codex_protocol::ResponseItemId;
     use codex_protocol::models::ContentItem;
     use codex_protocol::models::ResponseItem;
     use pretty_assertions::assert_eq;
@@ -905,7 +906,7 @@ mod tests {
             instructions: "Use the available tools.".to_string(),
             previous_response_id: Some("resp-1".to_string()),
             input: vec![ResponseItem::Message {
-                id: Some("msg-1".to_string()),
+                id: Some(ResponseItemId::with_suffix("msg", "1")),
                 role: "user".to_string(),
                 content: vec![ContentItem::InputText {
                     text: "hello".to_string(),

codex-rs/codex-api/src/endpoint/search.rs

@@ -70,6 +70,7 @@ mod tests {
     use codex_client::Response;
     use codex_client::StreamResponse;
     use codex_client::TransportError;
+    use codex_protocol::ResponseItemId;
     use codex_protocol::models::ContentItem;
     use codex_protocol::models::ResponseItem;
     use http::StatusCode;
@@ -150,7 +151,7 @@ mod tests {
                     model: "gpt-test".to_string(),
                     reasoning: None,
                     input: Some(SearchInput::Items(vec![ResponseItem::Message {
-                        id: Some("msg_search".to_string()),
+                        id: Some(ResponseItemId::with_suffix("msg", "search")),
                         role: "user".to_string(),
                         content: vec![
                             ContentItem::InputText {