Always assign response item IDs (#34645)

## What changed

- Assign IDs to client-created response items in every session, including streamed items, forked history, compaction results, and non-OpenAI provider requests.
- Preserve server-provided IDs and stable generated IDs across persisted and resumed conversations while continuing to omit unprefixed server IDs from outbound requests.
- Retire `features.item_ids` as a configurable feature. Existing configuration and CLI toggles remain accepted as compatibility no-ops.

## Testing

- Cover default ID assignment, persistence and resume behavior, remote compaction, provider requests, WebSocket requests, and removed-feature compatibility.

GitOrigin-RevId: 7a09e2d07d2606c2ef1e8e2283d36cb555557eae

codex-rs/core/src/thread_manager_tests.rs

@@ -31,6 +31,7 @@ use codex_utils_path_uri::PathUri;
 use core_test_support::PathBufExt;
 use core_test_support::PathExt;
 use core_test_support::responses::mount_models_once;
+use core_test_support::responses::strip_response_item_ids_from_json;
 use pretty_assertions::assert_eq;
 use std::time::Duration;
 use tempfile::tempdir;
@@ -1782,8 +1783,9 @@ async fn interrupted_fork_snapshot_does_not_synthesize_turn_id_for_legacy_histor
         rollout_items
             .iter()
             .filter(|item| {
-                serde_json::to_value(item).expect("serialize rollout item")
-                    == interrupted_marker_json
+                strip_response_item_ids_from_json(
+                    serde_json::to_value(item).expect("serialize rollout item"),
+                ) == interrupted_marker_json
             })
             .count(),
         1,
@@ -1986,8 +1988,9 @@ async fn interrupted_fork_snapshot_uses_persisted_mid_turn_history_without_live_
         forked_rollout_items
             .iter()
             .filter(|item| {
-                serde_json::to_value(item).expect("serialize forked rollout item")
-                    == interrupted_marker_json
+                strip_response_item_ids_from_json(
+                    serde_json::to_value(item).expect("serialize forked rollout item"),
+                ) == interrupted_marker_json
             })
             .count(),
         1,
@@ -2021,8 +2024,9 @@ async fn interrupted_fork_snapshot_uses_persisted_mid_turn_history_without_live_
         reforked_rollout_items
             .iter()
             .filter(|item| {
-                serde_json::to_value(item).expect("serialize re-forked rollout item")
-                    == interrupted_marker_json
+                strip_response_item_ids_from_json(
+                    serde_json::to_value(item).expect("serialize re-forked rollout item"),
+                ) == interrupted_marker_json
             })
             .count(),
         1,