Route response item IDs through a shared generator (#59312)

## What changed

Introduce `ItemIdGenerator` and pass the runtime-owned generator through sessions, model clients, history, hooks, tool outputs, and memory requests. Keep UUIDv7 generation as the default and replace direct calls to `ResponseItemId::new` with the shared callable.

Preserve existing item IDs and backfill missing or empty IDs through the same generator, including forked history before reconstruction and persistence.

## Testing

Extend coverage for UUIDv7 IDs on user messages, agent messages, and additional tools, and assert that forked model context matches the backfilled items persisted to history.

GitOrigin-RevId: 0dd9ccf0f46f0f1005a6acfc740133b03ce82259

codex-rs/protocol/src/item_id_generator.rs

@@ -0,0 +1,12 @@
+//! Response item ID generation shared by sessions and their consumers.
+
+use crate::ResponseItemId;
+use std::sync::Arc;
+
+/// Generates response item IDs from a type prefix for an owning session. Clones share the same callable.
+pub type ItemIdGenerator = Arc<dyn Fn(&str) -> ResponseItemId + Send + Sync>;
+
+#[cfg(test)]
+pub(super) fn uuid_v7_item_id_generator_for_test() -> ItemIdGenerator {
+    Arc::new(|prefix| ResponseItemId::with_suffix(prefix, uuid::Uuid::now_v7()))
+}

codex-rs/protocol/src/items.rs

@@ -1,5 +1,5 @@
 use crate::AgentPath;
-use crate::ResponseItemId;
+use crate::ItemIdGenerator;
 use crate::ThreadId;
 use crate::dynamic_tools::DynamicToolCallOutputContentItem;
 use crate::mcp::CallToolResult;
@@ -727,7 +727,10 @@ impl HookPromptFragment {
     }
 }
 
-pub fn build_hook_prompt_message(fragments: &[HookPromptFragment]) -> Option<ResponseItem> {
+pub fn build_hook_prompt_message(
+    fragments: &[HookPromptFragment],
+    item_id_generator: &ItemIdGenerator,
+) -> Option<ResponseItem> {
     let mut content = Vec::new();
     let mut metadata = Vec::new();
     for fragment in fragments {
@@ -744,7 +747,7 @@ pub fn build_hook_prompt_message(fragments: &[HookPromptFragment]) -> Option<Res
     Some(ResponseItem::Message {
         status: None,
         encrypted_content: None,
-        id: Some(ResponseItemId::new("msg")),
+        id: Some(item_id_generator("msg")),
         role: "user".to_string(),
         content,
         phase: None,
@@ -920,7 +923,9 @@ mod tests {
             HookPromptFragment::from_single_hook("Retry with care & joy.", "hook-run-1"),
             HookPromptFragment::from_single_hook("Then summarize cleanly.", "hook-run-2"),
         ];
-        let message = build_hook_prompt_message(&original).expect("hook prompt");
+        let message =
+            build_hook_prompt_message(&original, &crate::uuid_v7_item_id_generator_for_test())
+                .expect("hook prompt");
 
         let ResponseItem::Message { id, content, .. } = message else {
             panic!("expected hook prompt message");

codex-rs/protocol/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod account;
 mod agent_path;
 pub mod auth;
+mod item_id_generator;
 mod response_item_id;
 mod response_usage;
 mod sanitized_git_url;
@@ -8,6 +9,9 @@ mod session_id;
 mod thread_id;
 mod tool_name;
 pub use agent_path::AgentPath;
+pub use item_id_generator::ItemIdGenerator;
+#[cfg(test)]
+use item_id_generator::uuid_v7_item_id_generator_for_test;
 pub use permission_profile_intersection::PermissionIntersectionError;
 pub use permission_profile_intersection::intersect_effective_permission_profiles;
 pub use response_item_id::ResponseItemId;

codex-rs/protocol/src/models/configuration_update_tests.rs

@@ -1,5 +1,4 @@
 use super::ConfigurationReasoning;
-use crate::ResponseItemId;
 use crate::models::ResponseItem;
 use crate::openai_models::ReasoningEffort;
 use pretty_assertions::assert_eq;
@@ -21,7 +20,9 @@ fn configuration_update_round_trips_without_message_fields() {
         }
     );
 
-    item.set_id(Some(ResponseItemId::new("configuration-id")));
+    item.set_id(Some(crate::uuid_v7_item_id_generator_for_test()(
+        "configuration-id",
+    )));
     item.set_turn_id_if_missing("turn-id");
     item.set_create_time_if_missing(serde_json::Number::from(123));
     assert_eq!(

codex-rs/protocol/src/response_item_id.rs

@@ -17,10 +17,6 @@ use ts_rs::TS;
 pub struct ResponseItemId(String);
 
 impl ResponseItemId {
-    pub fn new(prefix: &str) -> Self {
-        Self::with_suffix(prefix, uuid::Uuid::now_v7())
-    }
-
     pub fn with_suffix(prefix: &str, suffix: impl fmt::Display) -> Self {
         Self(format!("{prefix}_{suffix}"))
     }

codex-rs/protocol/src/response_item_id_tests.rs

@@ -5,7 +5,7 @@ use super::ResponseItemId;
 
 #[test]
 fn creates_prefixed_uuid_v7_ids() {
-    let id = ResponseItemId::new("msg");
+    let id = crate::uuid_v7_item_id_generator_for_test()("msg");
     let uuid = id.strip_prefix("msg_").expect("message prefix");
     assert_eq!(
         Uuid::parse_str(uuid).expect("UUID suffix").get_version(),