Require prefixes for outbound response item IDs

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

@@ -447,7 +447,7 @@ impl ThreadHistoryBuilder {
             return;
         }
 
-        let Some(hook_prompt) = parse_hook_prompt_message(id.as_ref(), content) else {
+        let Some(hook_prompt) = parse_hook_prompt_message(id.as_deref(), content) else {
             return;
         };
 
@@ -4113,7 +4113,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             })),
             RolloutItem::ResponseItem(codex_protocol::models::ResponseItem::Message {
-                id: Some("msg-1".into()),
+                id: Some(codex_protocol::ResponseItemId::with_suffix("msg", "1")),
                 role: "user".into(),
                 content: vec![codex_protocol::models::ContentItem::InputText {
                     text: "plain text".into(),

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 {

codex-rs/codex-api/tests/clients.rs

@@ -19,6 +19,7 @@ use codex_client::RequestBody;
 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 codex_protocol::protocol::SessionSource;
@@ -309,7 +310,7 @@ async fn responses_client_stream_request_preserves_item_ids() -> Result<()> {
         model: "gpt-test".into(),
         instructions: "Say hi".into(),
         input: vec![ResponseItem::Message {
-            id: Some("msg_1".into()),
+            id: Some(ResponseItemId::with_suffix("msg", "1")),
             role: "user".into(),
             content: vec![ContentItem::InputText { text: "hi".into() }],
             phase: None,
@@ -516,7 +517,7 @@ async fn azure_store_sends_ids_and_headers() -> Result<()> {
         model: "gpt-test".into(),
         instructions: "Say hi".into(),
         input: vec![ResponseItem::Message {
-            id: Some("msg_1".into()),
+            id: Some(ResponseItemId::with_suffix("msg", "1")),
             role: "user".into(),
             content: vec![ContentItem::InputText { text: "hi".into() }],
             phase: None,

codex-rs/core/src/agent/control_tests.rs

@@ -19,6 +19,7 @@ use codex_features::Feature;
 use codex_login::AuthManager;
 use codex_login::CodexAuth;
 use codex_protocol::AgentPath;
+use codex_protocol::ResponseItemId;
 use codex_protocol::capabilities::CapabilityRootLocation;
 use codex_protocol::capabilities::SelectedCapabilityRoot;
 use codex_protocol::config_types::ModeKind;
@@ -979,7 +980,7 @@ async fn spawn_agent_can_fork_parent_thread_history_with_sanitized_items() {
                 assistant_message("parent final answer", Some(MessagePhase::FinalAnswer)),
                 assistant_message("parent unknown phase", /*phase*/ None),
                 ResponseItem::Reasoning {
-                    id: Some("parent-reasoning".to_string()),
+                    id: Some(ResponseItemId::with_suffix("rs", "parent-reasoning")),
                     summary: Vec::new(),
                     content: None,
                     encrypted_content: None,

codex-rs/core/src/client.rs

@@ -908,6 +908,12 @@ impl ModelClient {
     }
 
     fn prepare_response_items_for_request(&self, input: &mut [ResponseItem], store: bool) {
+        for item in input.iter_mut() {
+            if item.id().is_some_and(|id| !id.is_prefixed()) {
+                item.set_id(/*new_id*/ None);
+            }
+        }
+
         if self.state.item_ids_enabled || store {
             return;
         }

codex-rs/core/src/client_tests.rs

@@ -414,7 +414,7 @@ fn started_inference_attempt(temp: &TempDir) -> anyhow::Result<InferenceTraceAtt
 
 fn output_message(id: &str, text: &str) -> ResponseItem {
     ResponseItem::Message {
-        id: Some(id.to_string()),
+        id: Some(codex_protocol::ResponseItemId::with_suffix("msg", id)),
         role: "assistant".to_string(),
         content: vec![ContentItem::OutputText {
             text: text.to_string(),
@@ -581,7 +581,7 @@ async fn dropped_response_stream_traces_cancelled_partial_output() -> anyhow::Re
     // response.completed event. The harness has enough information to keep this
     // item in history, so the trace should preserve it when the stream is
     // abandoned.
-    let item = output_message("msg-1", "partial answer");
+    let item = output_message("1", "partial answer");
     let api_stream = futures::stream::iter([Ok(ResponseEvent::OutputItemDone(item))])
         .chain(futures::stream::pending());
     let (mut stream, _) = super::map_response_events(
@@ -699,7 +699,7 @@ async fn dropped_backpressured_response_stream_traces_cancelled_partial_output()
         events.push_back(ResponseEvent::Created);
     }
     events.push_back(ResponseEvent::OutputItemDone(output_message(
-        "msg-1",
+        "1",
         "partial answer",
     )));
     let api_stream = NotifyAfterEventStream {

codex-rs/core/src/compact_remote.rs

@@ -434,13 +434,14 @@ fn rewritten_output_for_context_window(item: &ResponseItem) -> Option<ResponseIt
             internal_chat_message_metadata_passthrough: metadata.clone(),
         },
         ResponseItem::ToolSearchOutput {
+            id,
             call_id,
             status,
             execution,
             internal_chat_message_metadata_passthrough: metadata,
             ..
         } => ResponseItem::ToolSearchOutput {
-            id: item.id().map(str::to_string),
+            id: id.clone(),
             call_id: call_id.clone(),
             status: status.clone(),
             execution: execution.clone(),

codex-rs/core/src/compact_tests.rs

@@ -2,6 +2,7 @@ use super::*;
 use crate::session::tests::build_world_state_from_turn_context;
 use codex_model_provider_info::ModelProviderInfo;
 use codex_model_provider_info::WireApi;
+use codex_protocol::ResponseItemId;
 use codex_protocol::models::DEFAULT_IMAGE_DETAIL;
 use codex_protocol::models::InternalChatMessageMetadataPassthrough;
 use pretty_assertions::assert_eq;
@@ -85,7 +86,7 @@ fn content_items_to_text_ignores_image_only_content() {
 fn collect_user_messages_extracts_user_text_only() {
     let items = vec![
         ResponseItem::Message {
-            id: Some("assistant".to_string()),
+            id: Some(ResponseItemId::with_suffix("msg", "assistant")),
             role: "assistant".to_string(),
             content: vec![ContentItem::OutputText {
                 text: "ignored".to_string(),
@@ -94,7 +95,7 @@ fn collect_user_messages_extracts_user_text_only() {
             internal_chat_message_metadata_passthrough: None,
         },
         ResponseItem::Message {
-            id: Some("user".to_string()),
+            id: Some(ResponseItemId::with_suffix("msg", "user")),
             role: "user".to_string(),
             content: vec![ContentItem::InputText {
                 text: "first".to_string(),

codex-rs/core/src/context/contextual_user_message.rs

@@ -75,7 +75,7 @@ pub(crate) fn is_contextual_user_fragment(content_item: &ContentItem) -> bool {
 }
 
 pub(crate) fn parse_visible_hook_prompt_message(
-    id: Option<&String>,
+    id: Option<&str>,
     content: &[ContentItem],
 ) -> Option<HookPromptItem> {
     let mut fragments = Vec::new();

codex-rs/core/src/context_manager/history_tests.rs

@@ -5,6 +5,7 @@ use crate::context::world_state::WorldStateSection;
 use base64::Engine;
 use base64::engine::general_purpose::STANDARD as BASE64_STANDARD;
 use codex_protocol::AgentPath;
+use codex_protocol::ResponseItemId;
 use codex_protocol::models::BaseInstructions;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::DEFAULT_IMAGE_DETAIL;
@@ -639,7 +640,7 @@ fn for_prompt_strips_images_when_model_does_not_support_images() {
 fn for_prompt_preserves_image_generation_calls_when_images_are_supported() {
     let history = create_history_with_items(vec![
         ResponseItem::ImageGenerationCall {
-            id: Some("ig_123".to_string()),
+            id: Some(ResponseItemId::with_suffix("ig", "123")),
             status: "generating".to_string(),
             revised_prompt: Some("lobster".to_string()),
             result: "Zm9v".to_string(),
@@ -660,7 +661,7 @@ fn for_prompt_preserves_image_generation_calls_when_images_are_supported() {
         history.for_prompt(&default_input_modalities()),
         vec![
             ResponseItem::ImageGenerationCall {
-                id: Some("ig_123".to_string()),
+                id: Some(ResponseItemId::with_suffix("ig", "123")),
                 status: "generating".to_string(),
                 revised_prompt: Some("lobster".to_string()),
                 result: "Zm9v".to_string(),
@@ -692,7 +693,7 @@ fn for_prompt_clears_image_generation_result_when_images_are_unsupported() {
             internal_chat_message_metadata_passthrough: None,
         },
         ResponseItem::ImageGenerationCall {
-            id: Some("ig_123".to_string()),
+            id: Some(ResponseItemId::with_suffix("ig", "123")),
             status: "completed".to_string(),
             revised_prompt: Some("lobster".to_string()),
             result: "Zm9v".to_string(),
@@ -713,7 +714,7 @@ fn for_prompt_clears_image_generation_result_when_images_are_unsupported() {
                 internal_chat_message_metadata_passthrough: None,
             },
             ResponseItem::ImageGenerationCall {
-                id: Some("ig_123".to_string()),
+                id: Some(ResponseItemId::with_suffix("ig", "123")),
                 status: "completed".to_string(),
                 revised_prompt: Some("lobster".to_string()),
                 result: String::new(),
@@ -1642,15 +1643,15 @@ fn normalize_adds_missing_output_for_function_call_inserts_output() {
 fn for_prompt_assigns_stable_id_to_synthetic_output_without_reordering_history() {
     let items = vec![
         ResponseItem::FunctionCall {
-            id: Some("fc_existing".to_string()),
+            id: Some(ResponseItemId::with_suffix("fc", "existing")),
             name: "do_it".to_string(),
             namespace: None,
             arguments: "{}".to_string(),
             call_id: "call-x".to_string(),
             internal_chat_message_metadata_passthrough: None,
         },
         ResponseItem::Message {
-            id: Some("msg_later".to_string()),
+            id: Some(ResponseItemId::with_suffix("msg", "later")),
             role: "user".to_string(),
             content: vec![ContentItem::InputText {
                 text: "later turn".to_string(),

codex-rs/core/src/context_manager/normalize.rs

@@ -1,3 +1,4 @@
+use codex_protocol::ResponseItemId;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::FunctionCallOutputPayload;
@@ -132,12 +133,12 @@ pub(crate) fn ensure_call_outputs_present(items: &mut Vec<ResponseItem>) {
 /// outputs, so the namespace and name format must remain stable across retries
 /// and resumes to preserve prompt-cache reuse. Returning `None` when the source
 /// call has no ID preserves the legacy behavior for older history items.
-fn synthetic_output_id(prefix: &str, item_id: Option<&str>) -> Option<String> {
+fn synthetic_output_id(prefix: &str, item_id: Option<&str>) -> Option<ResponseItemId> {
     let source_id = item_id.filter(|id| !id.is_empty())?;
     let name = format!("{prefix}:{source_id}");
-    Some(format!(
-        "{prefix}_{}",
-        Uuid::new_v5(&SYNTHETIC_OUTPUT_ID_NAMESPACE, name.as_bytes())
+    Some(ResponseItemId::with_suffix(
+        prefix,
+        Uuid::new_v5(&SYNTHETIC_OUTPUT_ID_NAMESPACE, name.as_bytes()),
     ))
 }