Preserve allocated response item IDs in requests (#60977)

## Why

Providers can echo a bare reserved prefix or return an opaque item ID. Request preparation previously stripped these IDs when they lacked an underscore prefix, even if they carried allocation metadata.

## What changed

- Keep response item IDs with allocation metadata when preparing requests.
- Add `ResponseItemId::with_generation_prefix` to attach a request reservation's allocation while preserving the exact wire ID and recording a matching item-kind prefix and provider suffix.

GitOrigin-RevId: 3249c2669aca11ee5facbd8a246016490a29a4f4

codex-rs/core/src/client.rs

@@ -1317,7 +1317,11 @@ impl ModelClient {
 
     fn prepare_response_items_for_request(&self, input: &mut [ResponseItem]) {
         for item in input {
-            if item.id().is_some_and(|id| !id.is_prefixed()) {
+            // A provider can echo a bare reserved prefix or return an opaque ID.
+            if item
+                .id()
+                .is_some_and(|id| id.allocation().is_none() && !id.is_prefixed())
+            {
                 item.set_id(/*new_id*/ None);
             }
             if !self.state.content_item_kinds_enabled {
@@ -2744,9 +2748,10 @@ fn map_response_stream(
     let routing_affinity = api_stream.routing_affinity.take();
     let upstream_request_id = api_stream.upstream_request_id.take();
     let interrupt = api_stream.interrupt.take();
+    let events = crate::model_request::intercept_stream(Box::pin(api_stream), interceptors);
     let mut stream = map_response_events(
         upstream_request_id,
-        crate::model_request::intercept_stream(Box::pin(api_stream), interceptors),
+        events,
         session_telemetry,
         inference_trace_attempt,
         client,