[codex] Add user input client ids (#24653)

## Summary

Adds an optional `clientId` field to app-server v2 `UserInput` and
carries it through the core `UserInput` model so clients can correlate
echoed user input items without relying on payload equality.

## Details

- Adds `client_id: Option<String>` to core `UserInput` variants.
- Exposes the v2 app-server field as `clientId` on the wire and in
generated TypeScript.
- Preserves the id when converting between app-server v2 and core
protocol types.
- Regenerates app-server schema fixtures.

## Validation

- `just fmt`
- `just write-app-server-schema`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-protocol`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-protocol`
- `git diff --check`

codex-rs/analytics/src/analytics_client_tests.rs

@@ -272,6 +272,7 @@ fn sample_turn_start_request(thread_id: &str, request_id: i64) -> ClientRequest
         request_id: RequestId::Integer(request_id),
         params: TurnStartParams {
             thread_id: thread_id.to_string(),
+            client_user_message_id: None,
             input: vec![
                 UserInput::Text {
                     text: "hello".to_string(),
@@ -391,6 +392,7 @@ fn sample_turn_steer_request(
         params: TurnSteerParams {
             thread_id: thread_id.to_string(),
             expected_turn_id: expected_turn_id.to_string(),
+            client_user_message_id: None,
             input: vec![
                 UserInput::Text {
                     text: "more".to_string(),

codex-rs/analytics/src/client_tests.rs

@@ -89,6 +89,7 @@ fn sample_turn_start_request() -> ClientRequest {
         request_id: RequestId::Integer(1),
         params: TurnStartParams {
             thread_id: "thread-1".to_string(),
+            client_user_message_id: None,
             input: Vec::new(),
             ..Default::default()
         },
@@ -101,6 +102,7 @@ fn sample_turn_steer_request() -> ClientRequest {
         params: TurnSteerParams {
             thread_id: "thread-1".to_string(),
             expected_turn_id: "turn-1".to_string(),
+            client_user_message_id: None,
             input: Vec::new(),
             responsesapi_client_metadata: None,
             additional_context: None,

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -3985,6 +3985,12 @@
           ],
           "description": "Override where approval requests are routed for review on this turn and subsequent turns."
         },
+        "clientUserMessageId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "cwd": {
           "description": "Override the working directory for this turn and subsequent turns.",
           "type": [
@@ -4071,6 +4077,12 @@
     },
     "TurnSteerParams": {
       "properties": {
+        "clientUserMessageId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "expectedTurnId": {
           "description": "Required active turn id precondition. The request fails when it does not match the currently active turn.",
           "type": "string"

codex-rs/app-server-protocol/schema/json/ServerNotification.json

@@ -3561,6 +3561,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -15996,6 +15996,12 @@
         "oneOf": [
           {
             "properties": {
+              "clientId": {
+                "type": [
+                  "string",
+                  "null"
+                ]
+              },
               "content": {
                 "items": {
                   "$ref": "#/definitions/v2/UserInput"
@@ -18413,6 +18419,12 @@
             ],
             "description": "Override where approval requests are routed for review on this turn and subsequent turns."
           },
+          "clientUserMessageId": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
           "cwd": {
             "description": "Override the working directory for this turn and subsequent turns.",
             "type": [
@@ -18540,6 +18552,12 @@
       "TurnSteerParams": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "properties": {
+          "clientUserMessageId": {
+            "type": [
+              "string",
+              "null"
+            ]
+          },
           "expectedTurnId": {
             "description": "Required active turn id precondition. The request fails when it does not match the currently active turn.",
             "type": "string"

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -13820,6 +13820,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"
@@ -16237,6 +16243,12 @@
           ],
           "description": "Override where approval requests are routed for review on this turn and subsequent turns."
         },
+        "clientUserMessageId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "cwd": {
           "description": "Override the working directory for this turn and subsequent turns.",
           "type": [
@@ -16364,6 +16376,12 @@
     "TurnSteerParams": {
       "$schema": "http://json-schema.org/draft-07/schema#",
       "properties": {
+        "clientUserMessageId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "expectedTurnId": {
           "description": "Required active turn id precondition. The request fails when it does not match the currently active turn.",
           "type": "string"

codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json

@@ -500,6 +500,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json

@@ -500,6 +500,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json

@@ -644,6 +644,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json

@@ -1121,6 +1121,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json

@@ -936,6 +936,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json

@@ -936,6 +936,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json

@@ -936,6 +936,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json

@@ -1121,6 +1121,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadRollbackResponse.json

@@ -936,6 +936,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json

@@ -1121,6 +1121,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json

@@ -936,6 +936,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json

@@ -936,6 +936,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json

@@ -644,6 +644,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/TurnStartParams.json

@@ -516,6 +516,12 @@
       ],
       "description": "Override where approval requests are routed for review on this turn and subsequent turns."
     },
+    "clientUserMessageId": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
     "cwd": {
       "description": "Override the working directory for this turn and subsequent turns.",
       "type": [

codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json

@@ -644,6 +644,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json

@@ -644,6 +644,12 @@
       "oneOf": [
         {
           "properties": {
+            "clientId": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "content": {
               "items": {
                 "$ref": "#/definitions/UserInput"

codex-rs/app-server-protocol/schema/json/v2/TurnSteerParams.json

@@ -218,6 +218,12 @@
     }
   },
   "properties": {
+    "clientUserMessageId": {
+      "type": [
+        "string",
+        "null"
+      ]
+    },
     "expectedTurnId": {
       "description": "Required active turn id precondition. The request fails when it does not match the currently active turn.",
       "type": "string"

codex-rs/app-server-protocol/schema/typescript/v2/ThreadItem.ts

@@ -23,7 +23,7 @@ import type { PatchApplyStatus } from "./PatchApplyStatus";
 import type { UserInput } from "./UserInput";
 import type { WebSearchAction } from "./WebSearchAction";
 
-export type ThreadItem = { "type": "userMessage", id: string, content: Array<UserInput>, } | { "type": "hookPrompt", id: string, fragments: Array<HookPromptFragment>, } | { "type": "agentMessage", id: string, text: string, phase: MessagePhase | null, memoryCitation: MemoryCitation | null, } | { "type": "plan", id: string, text: string, } | { "type": "reasoning", id: string, summary: Array<string>, content: Array<string>, } | { "type": "commandExecution", id: string,
+export type ThreadItem = { "type": "userMessage", id: string, clientId: string | null, content: Array<UserInput>, } | { "type": "hookPrompt", id: string, fragments: Array<HookPromptFragment>, } | { "type": "agentMessage", id: string, text: string, phase: MessagePhase | null, memoryCitation: MemoryCitation | null, } | { "type": "plan", id: string, text: string, } | { "type": "reasoning", id: string, summary: Array<string>, content: Array<string>, } | { "type": "commandExecution", id: string,
 /**
  * The command to be executed.
  */

codex-rs/app-server-protocol/schema/typescript/v2/TurnStartParams.ts

@@ -10,7 +10,7 @@ import type { AskForApproval } from "./AskForApproval";
 import type { SandboxPolicy } from "./SandboxPolicy";
 import type { UserInput } from "./UserInput";
 
-export type TurnStartParams = {threadId: string, input: Array<UserInput>, /**
+export type TurnStartParams = {threadId: string, clientUserMessageId?: string | null, input: Array<UserInput>, /**
  * Override the working directory for this turn and subsequent turns.
  */
 cwd?: string | null, /**

codex-rs/app-server-protocol/schema/typescript/v2/TurnSteerParams.ts

@@ -3,7 +3,7 @@
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 import type { UserInput } from "./UserInput";
 
-export type TurnSteerParams = {threadId: string, input: Array<UserInput>, /**
+export type TurnSteerParams = {threadId: string, clientUserMessageId?: string | null, input: Array<UserInput>, /**
  * Required active turn id precondition. The request fails when it does not
  * match the currently active turn.
  */

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

@@ -278,7 +278,11 @@ impl ThreadHistoryBuilder {
             .unwrap_or_else(|| self.new_turn(/*id*/ None));
         let id = self.next_item_id();
         let content = self.build_user_inputs(payload);
-        turn.items.push(ThreadItem::UserMessage { id, content });
+        turn.items.push(ThreadItem::UserMessage {
+            id,
+            client_id: payload.client_id.clone(),
+            content,
+        });
         self.current_turn = Some(turn);
     }
 
@@ -1246,6 +1250,7 @@ mod tests {
     fn builds_multiple_turns_with_reasoning_items() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "First turn".into(),
                 images: Some(vec!["https://example.com/one.png".into()]),
                 text_elements: Vec::new(),
@@ -1264,6 +1269,7 @@ mod tests {
                 text: "full reasoning".into(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Second turn".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1292,6 +1298,7 @@ mod tests {
             first.items[0],
             ThreadItem::UserMessage {
                 id: "item-1".into(),
+                client_id: None,
                 content: vec![
                     UserInput::Text {
                         text: "First turn".into(),
@@ -1330,6 +1337,7 @@ mod tests {
             second.items[0],
             ThreadItem::UserMessage {
                 id: "item-4".into(),
+                client_id: None,
                 content: vec![UserInput::Text {
                     text: "Second turn".into(),
                     text_elements: Vec::new(),
@@ -1352,6 +1360,7 @@ mod tests {
         let local_path = PathBuf::from("/tmp/local.png");
         let events = vec![RolloutItem::EventMsg(EventMsg::UserMessage(
             UserMessageEvent {
+                client_id: None,
                 message: "inspect these".into(),
                 images: Some(vec!["https://example.com/image.png".into()]),
                 image_details: vec![Some(ImageDetail::Original)],
@@ -1368,6 +1377,7 @@ mod tests {
             turns[0].items[0],
             ThreadItem::UserMessage {
                 id: "item-1".into(),
+                client_id: None,
                 content: vec![
                     UserInput::Text {
                         text: "inspect these".into(),
@@ -1399,6 +1409,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "hello".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1410,6 +1421,7 @@ mod tests {
                 turn_id: turn_id.to_string(),
                 item: CoreTurnItem::UserMessage(CoreUserMessageItem {
                     id: "user-item-id".to_string(),
+                    client_id: None,
                     content: Vec::new(),
                 }),
                 started_at_ms: 0,
@@ -1434,6 +1446,7 @@ mod tests {
             turns[0].items[0],
             ThreadItem::UserMessage {
                 id: "item-1".into(),
+                client_id: None,
                 content: vec![UserInput::Text {
                     text: "hello".into(),
                     text_elements: Vec::new(),
@@ -1442,6 +1455,67 @@ mod tests {
         );
     }
 
+    #[test]
+    fn preserves_user_message_client_id_from_legacy_event() {
+        let turn_id = "turn-1";
+        let thread_id = ThreadId::new();
+        let events = vec![
+            EventMsg::TurnStarted(TurnStartedEvent {
+                turn_id: turn_id.to_string(),
+                trace_id: None,
+                started_at: None,
+                model_context_window: None,
+                collaboration_mode_kind: Default::default(),
+            }),
+            EventMsg::ItemStarted(ItemStartedEvent {
+                thread_id,
+                turn_id: turn_id.to_string(),
+                item: CoreTurnItem::UserMessage(CoreUserMessageItem {
+                    id: "user-item-id".to_string(),
+                    client_id: Some("client-message-1".to_string()),
+                    content: vec![codex_protocol::user_input::UserInput::Text {
+                        text: "hello".into(),
+                        text_elements: Vec::new(),
+                    }],
+                }),
+                started_at_ms: 0,
+            }),
+            EventMsg::UserMessage(UserMessageEvent {
+                client_id: Some("client-message-1".to_string()),
+                message: "hello".into(),
+                images: None,
+                text_elements: Vec::new(),
+                local_images: Vec::new(),
+                ..Default::default()
+            }),
+            EventMsg::TurnComplete(TurnCompleteEvent {
+                turn_id: turn_id.to_string(),
+                last_agent_message: None,
+                completed_at: None,
+                duration_ms: None,
+                time_to_first_token_ms: None,
+            }),
+        ];
+
+        let items = events
+            .into_iter()
+            .map(RolloutItem::EventMsg)
+            .collect::<Vec<_>>();
+        let turns = build_turns_from_rollout_items(&items);
+        assert_eq!(turns.len(), 1);
+        assert_eq!(
+            turns[0].items,
+            vec![ThreadItem::UserMessage {
+                id: "item-1".into(),
+                client_id: Some("client-message-1".to_string()),
+                content: vec![UserInput::Text {
+                    text: "hello".into(),
+                    text_elements: Vec::new(),
+                }],
+            }]
+        );
+    }
+
     #[test]
     fn preserves_agent_message_phase_in_history() {
         let events = vec![EventMsg::AgentMessage(AgentMessageEvent {
@@ -1478,6 +1552,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             })),
             RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "generate an image".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1515,6 +1590,7 @@ mod tests {
                 items: vec![
                     ThreadItem::UserMessage {
                         id: "item-1".into(),
+                        client_id: None,
                         content: vec![UserInput::Text {
                             text: "generate an image".into(),
                             text_elements: Vec::new(),
@@ -1536,6 +1612,7 @@ mod tests {
     fn splits_reasoning_when_interleaved() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Turn start".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1589,6 +1666,7 @@ mod tests {
     fn marks_turn_as_interrupted_when_aborted() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Please do the thing".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1607,6 +1685,7 @@ mod tests {
                 duration_ms: None,
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Let's try again".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1634,6 +1713,7 @@ mod tests {
             first_turn.items[0],
             ThreadItem::UserMessage {
                 id: "item-1".into(),
+                client_id: None,
                 content: vec![UserInput::Text {
                     text: "Please do the thing".into(),
                     text_elements: Vec::new(),
@@ -1657,6 +1737,7 @@ mod tests {
             second_turn.items[0],
             ThreadItem::UserMessage {
                 id: "item-3".into(),
+                client_id: None,
                 content: vec![UserInput::Text {
                     text: "Let's try again".into(),
                     text_elements: Vec::new(),
@@ -1678,6 +1759,7 @@ mod tests {
     fn drops_last_turns_on_thread_rollback() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "First".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1690,6 +1772,7 @@ mod tests {
                 memory_citation: None,
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Second".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1703,6 +1786,7 @@ mod tests {
             }),
             EventMsg::ThreadRolledBack(ThreadRolledBackEvent { num_turns: 1 }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Third".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1732,6 +1816,7 @@ mod tests {
             vec![
                 ThreadItem::UserMessage {
                     id: "item-1".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "First".into(),
                         text_elements: Vec::new(),
@@ -1750,6 +1835,7 @@ mod tests {
             vec![
                 ThreadItem::UserMessage {
                     id: "item-3".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "Third".into(),
                         text_elements: Vec::new(),
@@ -1769,6 +1855,7 @@ mod tests {
     fn thread_rollback_clears_all_turns_when_num_turns_exceeds_history() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "One".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1781,6 +1868,7 @@ mod tests {
                 memory_citation: None,
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Two".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1814,6 +1902,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Start".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1821,6 +1910,7 @@ mod tests {
                 ..Default::default()
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "Steer".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -1848,6 +1938,7 @@ mod tests {
             vec![
                 ThreadItem::UserMessage {
                     id: "item-1".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "Start".into(),
                         text_elements: Vec::new(),
@@ -1855,6 +1946,7 @@ mod tests {
                 },
                 ThreadItem::UserMessage {
                     id: "item-2".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "Steer".into(),
                         text_elements: Vec::new(),
@@ -1875,6 +1967,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "run tools".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2054,6 +2147,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "run dynamic tool".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2121,6 +2215,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "run tools".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2212,6 +2307,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "review this command".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2297,6 +2393,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "run a subcommand".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2362,6 +2459,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "first".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2383,6 +2481,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "second".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2458,6 +2557,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "first".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2479,6 +2579,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "second".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2528,6 +2629,7 @@ mod tests {
             turns[1].items[0],
             ThreadItem::UserMessage {
                 id: "item-2".into(),
+                client_id: None,
                 content: vec![UserInput::Text {
                     text: "second".into(),
                     text_elements: Vec::new(),
@@ -2549,6 +2651,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "apply patch".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2584,6 +2687,7 @@ mod tests {
             vec![
                 ThreadItem::UserMessage {
                     id: "item-1".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "apply patch".into(),
                         text_elements: Vec::new(),
@@ -2615,6 +2719,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "apply patch".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2652,6 +2757,7 @@ mod tests {
             vec![
                 ThreadItem::UserMessage {
                     id: "item-1".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "apply patch".into(),
                         text_elements: Vec::new(),
@@ -2681,6 +2787,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "first".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2702,6 +2809,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "second".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2751,6 +2859,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "first".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2772,6 +2881,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "second".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2846,6 +2956,7 @@ mod tests {
     fn reconstructs_collab_resume_end_item() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "resume agent".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2904,6 +3015,7 @@ mod tests {
             .expect("valid receiver thread id");
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "spawn agent".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -2966,6 +3078,7 @@ mod tests {
             .expect("valid receiver thread id");
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "redirect".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -3030,6 +3143,7 @@ mod tests {
     fn rollback_failed_error_does_not_mark_turn_failed() {
         let events = vec![
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "hello".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -3068,6 +3182,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "hello".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -3105,6 +3220,7 @@ mod tests {
                 items_view: TurnItemsView::Full,
                 items: vec![ThreadItem::UserMessage {
                     id: "item-1".into(),
+                    client_id: None,
                     content: vec![UserInput::Text {
                         text: "hello".into(),
                         text_elements: Vec::new(),
@@ -3125,6 +3241,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             }),
             EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "hello".into(),
                 images: None,
                 text_elements: Vec::new(),
@@ -3184,6 +3301,7 @@ mod tests {
                 collaboration_mode_kind: Default::default(),
             })),
             RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "hello".into(),
                 images: None,
                 text_elements: Vec::new(),

codex-rs/app-server-protocol/src/protocol/v2/item.rs

@@ -212,7 +212,11 @@ impl CommandAction {
 pub enum ThreadItem {
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
-    UserMessage { id: String, content: Vec<UserInput> },
+    UserMessage {
+        id: String,
+        client_id: Option<String>,
+        content: Vec<UserInput>,
+    },
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
     HookPrompt {
@@ -776,6 +780,7 @@ impl From<CoreTurnItem> for ThreadItem {
         match value {
             CoreTurnItem::UserMessage(user) => ThreadItem::UserMessage {
                 id: user.id,
+                client_id: user.client_id,
                 content: user.content.into_iter().map(UserInput::from).collect(),
             },
             CoreTurnItem::HookPrompt(hook_prompt) => ThreadItem::HookPrompt {

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -1756,6 +1756,7 @@ fn client_request_turn_start_granular_approval_policy_is_marked_experimental() {
             request_id: crate::RequestId::Integer(4),
             params: TurnStartParams {
                 thread_id: "thr_123".to_string(),
+                client_user_message_id: None,
                 input: Vec::new(),
                 approval_policy: Some(AskForApproval::Granular {
                     sandbox_approval: false,
@@ -2314,6 +2315,7 @@ fn network_requirements_serializes_canonical_and_legacy_fields() {
 fn core_turn_item_into_thread_item_converts_supported_variants() {
     let user_item = TurnItem::UserMessage(UserMessageItem {
         id: "user-1".to_string(),
+        client_id: Some("client-message-1".to_string()),
         content: vec![
             CoreUserInput::Text {
                 text: "hello".to_string(),
@@ -2342,6 +2344,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
         ThreadItem::from(user_item),
         ThreadItem::UserMessage {
             id: "user-1".to_string(),
+            client_id: Some("client-message-1".to_string()),
             content: vec![
                 UserInput::Text {
                     text: "hello".to_string(),
@@ -3582,6 +3585,7 @@ fn turn_start_params_preserve_explicit_null_service_tier() {
 
     let without_override = TurnStartParams {
         thread_id: "thread_123".to_string(),
+        client_user_message_id: None,
         input: vec![],
         responsesapi_client_metadata: None,
         additional_context: None,

codex-rs/app-server-protocol/src/protocol/v2/turn.rs

@@ -65,6 +65,8 @@ pub struct AdditionalContextEntry {
 #[ts(export_to = "v2/")]
 pub struct TurnStartParams {
     pub thread_id: String,
+    #[ts(optional = nullable)]
+    pub client_user_message_id: Option<String>,
     pub input: Vec<UserInput>,
     /// Optional turn-scoped Responses API client metadata.
     #[experimental("turn/start.responsesapiClientMetadata")]
@@ -157,6 +159,8 @@ pub struct TurnStartResponse {
 #[ts(export_to = "v2/")]
 pub struct TurnSteerParams {
     pub thread_id: String,
+    #[ts(optional = nullable)]
+    pub client_user_message_id: Option<String>,
     pub input: Vec<UserInput>,
     /// Optional turn-scoped Responses API client metadata.
     #[experimental("turn/steer.responsesapiClientMetadata")]

codex-rs/app-server-test-client/src/lib.rs

@@ -734,6 +734,7 @@ async fn trigger_zsh_fork_multi_cmd_approval(
 
             let mut turn_params = TurnStartParams {
                 thread_id: thread_response.thread.id.clone(),
+                client_user_message_id: None,
                 input: vec![V2UserInput::Text {
                     text: message,
                     text_elements: Vec::new(),
@@ -818,6 +819,7 @@ async fn resume_message_v2(
 
         let turn_response = client.turn_start(TurnStartParams {
             thread_id: resume_response.thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: user_message,
                 text_elements: Vec::new(),
@@ -959,6 +961,7 @@ async fn send_message_v2_with_policies(
             println!("< thread/start response: {thread_response:?}");
             let mut turn_params = TurnStartParams {
                 thread_id: thread_response.thread.id.clone(),
+                client_user_message_id: None,
                 input: vec![V2UserInput::Text {
                     text: user_message,
                     // Test client sends plain text without UI element ranges.
@@ -999,6 +1002,7 @@ async fn send_follow_up_v2(
 
         let first_turn_params = TurnStartParams {
             thread_id: thread_response.thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: first_message,
                 // Test client sends plain text without UI element ranges.
@@ -1012,6 +1016,7 @@ async fn send_follow_up_v2(
 
         let follow_up_params = TurnStartParams {
             thread_id: thread_response.thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: follow_up_message,
                 // Test client sends plain text without UI element ranges.
@@ -1255,6 +1260,7 @@ fn live_elicitation_timeout_pause(
     let started_at = Instant::now();
     let turn_response = client.turn_start(TurnStartParams {
         thread_id: thread_id.clone(),
+        client_user_message_id: None,
         input: vec![V2UserInput::Text {
             text: prompt,
             text_elements: Vec::new(),

codex-rs/app-server/README.md

@@ -158,9 +158,9 @@ Example with notification opt-out:
 - `thread/shellCommand` — run a user-initiated `!` shell command against a thread; this runs unsandboxed with full access rather than inheriting the thread sandbox policy. Returns `{}` immediately while progress streams through standard turn/item notifications and any active turn receives the formatted output in its message stream.
 - `thread/backgroundTerminals/clean` — terminate all running background terminals for a thread (experimental; requires `capabilities.experimentalApi`); returns `{}` when the cleanup request is accepted.
 - `thread/rollback` — drop the last N turns from the agent’s in-memory context and persist a rollback marker in the rollout so future resumes see the pruned history; returns the updated `thread` (with `turns` populated) on success.
-- `turn/start` — add user input to a thread and begin Codex generation; responds with the initial `turn` object and streams `turn/started`, `item/*`, and `turn/completed` notifications. Experimental `runtimeWorkspaceRoots` replaces the thread-scoped runtime workspace roots used to materialize `:workspace_roots`; relative paths resolve against the effective turn cwd. Prefer experimental `permissions` profile selection by id for permission overrides; the legacy `sandboxPolicy` field is still accepted but cannot be combined with `permissions`. For `collaborationMode`, `settings.developer_instructions: null` means "use built-in instructions for the selected mode".
+- `turn/start` — add user input to a thread and begin Codex generation; responds with the initial `turn` object and streams `turn/started`, `item/*`, and `turn/completed` notifications. `clientUserMessageId` is optional; when supplied, the corresponding `userMessage` item echoes it as `clientId`. Experimental `runtimeWorkspaceRoots` replaces the thread-scoped runtime workspace roots used to materialize `:workspace_roots`; relative paths resolve against the effective turn cwd. Prefer experimental `permissions` profile selection by id for permission overrides; the legacy `sandboxPolicy` field is still accepted but cannot be combined with `permissions`. For `collaborationMode`, `settings.developer_instructions: null` means "use built-in instructions for the selected mode".
 - `thread/inject_items` — append raw Responses API items to a loaded thread’s model-visible history without starting a user turn; returns `{}` on success.
-- `turn/steer` — add user input to an already in-flight regular turn without starting a new turn; returns the active `turnId` that accepted the input. Review and manual compaction turns reject `turn/steer`.
+- `turn/steer` — add user input to an already in-flight regular turn without starting a new turn; returns the active `turnId` that accepted the input. `clientUserMessageId` is optional; when supplied, the corresponding `userMessage` item echoes it as `clientId`. Review and manual compaction turns reject `turn/steer`.
 - `turn/interrupt` — request cancellation of an in-flight turn by `(thread_id, turn_id)`; success is an empty `{}` response and the turn finishes with `status: "interrupted"`.
 - `thread/realtime/start` — start a thread-scoped realtime session (experimental); pass `outputModality: "text"` or `outputModality: "audio"` to choose model output, returns `{}` and streams `thread/realtime/*` notifications. Omit `transport` for the websocket transport, or pass `{ "type": "webrtc", "sdp": "..." }` to create a WebRTC session from a browser-generated SDP offer; the remote answer SDP is emitted as `thread/realtime/sdp`.
 - `thread/realtime/appendAudio` — append an input audio chunk to the active realtime session (experimental); returns `{}`.
@@ -662,6 +662,7 @@ You can optionally specify config overrides on the new turn. If specified, these
 ```json
 { "method": "turn/start", "id": 30, "params": {
     "threadId": "thr_123",
+    "clientUserMessageId": "client_msg_123",
     "input": [ { "type": "text", "text": "Run tests" } ],
     // Below are optional config overrides
     "cwd": "/Users/me/project",
@@ -860,6 +861,7 @@ not emit `turn/started` and does not accept thread settings overrides.
 ```json
 { "method": "turn/steer", "id": 32, "params": {
     "threadId": "thr_123",
+    "clientUserMessageId": "client_msg_124",
     "input": [ { "type": "text", "text": "Actually focus on failing tests first." } ],
     "expectedTurnId": "turn_456"
 } }
@@ -1245,7 +1247,7 @@ Today both notifications carry an empty `items` array even when item events were
 
 `ThreadItem` is the tagged union carried in turn responses and `item/*` notifications. Currently we support events for the following items:
 
-- `userMessage` — `{id, content}` where `content` is a list of user inputs (`text`, `image`, or `localImage`).
+- `userMessage` — `{id, clientId, content}` where `clientId` is the optional `clientUserMessageId` supplied to `turn/start` or `turn/steer`, and `content` is a list of user inputs (`text`, `image`, or `localImage`).
 - `agentMessage` — `{id, text}` containing the accumulated agent reply.
 - `plan` — `{id, text}` emitted for plan-mode turns; plan text can stream via `item/plan/delta` (experimental).
 - `reasoning` — `{id, summary, content}` where `summary` holds streamed reasoning summaries (applicable for most OpenAI models) and `content` holds raw reasoning blocks (applicable for e.g. open source models).

codex-rs/app-server/src/bespoke_event_handling.rs

@@ -2153,6 +2153,7 @@ mod tests {
         let created_at = Utc::now();
         let history_items = vec![
             RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "before rollback".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -3228,6 +3229,7 @@ mod tests {
             state.track_current_turn_event(
                 "turn-1",
                 &EventMsg::UserMessage(codex_protocol::protocol::UserMessageEvent {
+                    client_id: None,
                     message: "already tracked".to_string(),
                     images: None,
                     local_images: Vec::new(),

codex-rs/app-server/src/message_processor_tracing_tests.rs

@@ -653,6 +653,7 @@ async fn turn_start_jsonrpc_span_parents_core_turn_spans() -> Result<()> {
                 params: TurnStartParams {
                     environments: None,
                     thread_id,
+                    client_user_message_id: None,
                     input: vec![UserInput::Text {
                         text: "hello".to_string(),
                         text_elements: Vec::new(),

codex-rs/app-server/src/request_processors/thread_processor_tests.rs

@@ -213,6 +213,7 @@ mod thread_processor_behavior_tests {
     fn thread_turns_list_merges_in_progress_active_turn_before_agent_status_running() {
         let persisted_items = vec![RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "persisted".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -224,6 +225,7 @@ mod thread_processor_behavior_tests {
             id: "live-turn".to_string(),
             items: vec![ThreadItem::UserMessage {
                 id: "live-user-message".to_string(),
+                client_id: None,
                 content: vec![V2UserInput::Text {
                     text: "live".to_string(),
                     text_elements: Vec::new(),

codex-rs/app-server/src/request_processors/token_usage_replay.rs

@@ -148,6 +148,7 @@ mod tests {
     fn token_usage_history() -> Vec<RolloutItem> {
         vec![
             RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "first turn".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -164,6 +165,7 @@ mod tests {
                 rate_limits: None,
             })),
             RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "second turn".to_string(),
                 images: None,
                 local_images: Vec::new(),

codex-rs/app-server/src/request_processors/turn_processor.rs

@@ -416,6 +416,7 @@ impl TurnRequestProcessor {
             .into_iter()
             .map(V2UserInput::into_core)
             .collect();
+        let client_user_message_id = params.client_user_message_id;
         let additional_context = map_additional_context(params.additional_context);
         let turn_has_input = !mapped_items.is_empty();
         let thread_settings = self
@@ -448,8 +449,12 @@ impl TurnRequestProcessor {
             additional_context,
             thread_settings,
         };
-        let turn_id = self
-            .submit_core_op(&request_id, thread.as_ref(), turn_op)
+        let turn_id = thread
+            .submit_user_input_with_client_user_message_id(
+                turn_op,
+                self.request_trace_context(&request_id).await,
+                client_user_message_id,
+            )
             .await
             .map_err(|err| {
                 let error = internal_error(format!("failed to start turn: {err}"));
@@ -780,6 +785,7 @@ impl TurnRequestProcessor {
                 mapped_items,
                 additional_context,
                 Some(&params.expected_turn_id),
+                params.client_user_message_id,
                 params.responsesapi_client_metadata,
             )
             .await
@@ -989,6 +995,7 @@ impl TurnRequestProcessor {
         } else {
             vec![ThreadItem::UserMessage {
                 id: turn_id.clone(),
+                client_id: None,
                 content: vec![V2UserInput::Text {
                     text: display_text.to_string(),
                     // Review prompt display text is synthesized; no UI element ranges to preserve.

codex-rs/app-server/tests/suite/v2/account.rs

@@ -506,6 +506,7 @@ async fn external_auth_refreshes_on_unauthorized() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(codex_app_server_protocol::TurnStartParams {
             thread_id: thread.thread.id,
+            client_user_message_id: None,
             input: vec![codex_app_server_protocol::UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -612,6 +613,7 @@ async fn external_auth_refresh_error_fails_turn() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(codex_app_server_protocol::TurnStartParams {
             thread_id: thread.thread.id.clone(),
+            client_user_message_id: None,
             input: vec![codex_app_server_protocol::UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -734,6 +736,7 @@ async fn external_auth_refresh_mismatched_workspace_fails_turn() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(codex_app_server_protocol::TurnStartParams {
             thread_id: thread.thread.id.clone(),
+            client_user_message_id: None,
             input: vec![codex_app_server_protocol::UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -849,6 +852,7 @@ async fn external_auth_refresh_invalid_access_token_fails_turn() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(codex_app_server_protocol::TurnStartParams {
             thread_id: thread.thread.id.clone(),
+            client_user_message_id: None,
             input: vec![codex_app_server_protocol::UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/attestation.rs

@@ -110,6 +110,7 @@ async fn attestation_generate_round_trip_adds_header_to_responses_websocket_hand
     let turn_request_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/client_metadata.rs

@@ -73,6 +73,7 @@ async fn turn_start_forwards_client_metadata_to_responses_request_v2() -> Result
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -153,6 +154,7 @@ async fn turn_start_sends_fork_lineage_in_turn_metadata_for_thread_fork_v2() ->
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Continue".to_string(),
                 text_elements: Vec::new(),
@@ -333,6 +335,7 @@ async fn turn_steer_updates_client_metadata_on_follow_up_responses_request_v2()
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Run sleep".to_string(),
                 text_elements: Vec::new(),
@@ -363,6 +366,7 @@ async fn turn_steer_updates_client_metadata_on_follow_up_responses_request_v2()
     let steer_req = mcp
         .send_turn_steer_request(TurnSteerParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Focus on the failure".to_string(),
                 text_elements: Vec::new(),
@@ -458,6 +462,7 @@ async fn turn_start_forwards_client_metadata_to_responses_websocket_request_body
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/compaction.rs

@@ -394,6 +394,7 @@ async fn send_turn_and_wait(mcp: &mut McpProcess, thread_id: &str, text: &str) -
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.to_string(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: text.to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/connection_handling_websocket_unix.rs

@@ -226,6 +226,7 @@ async fn send_turn_start_request(stream: &mut WsClient, id: i64, thread_id: &str
         id,
         Some(serde_json::to_value(TurnStartParams {
             thread_id: thread_id.to_string(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/dynamic_tools.rs

@@ -89,6 +89,7 @@ async fn thread_start_injects_dynamic_tools_into_model_requests() -> Result<()>
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -168,6 +169,7 @@ async fn thread_start_keeps_hidden_dynamic_tools_out_of_model_requests() -> Resu
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -347,6 +349,7 @@ async fn dynamic_tool_call_round_trip_sends_text_content_items_to_model() -> Res
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Run the tool".to_string(),
                 text_elements: Vec::new(),
@@ -521,6 +524,7 @@ async fn dynamic_tool_call_round_trip_sends_content_items_to_model() -> Result<(
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Run the tool".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/external_agent_config.rs

@@ -391,6 +391,7 @@ async fn external_agent_config_import_creates_session_rollouts() -> Result<()> {
     let request_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "follow up".to_string(),
                 text_elements: Vec::new(),
@@ -964,6 +965,7 @@ async fn external_agent_config_import_compacts_huge_session_before_first_follow_
     let request_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "follow up".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/hooks_list.rs

@@ -662,6 +662,7 @@ command = "python3 {hook_script_path}"
     let first_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "first turn".to_string(),
                 text_elements: Vec::new(),
@@ -723,6 +724,7 @@ command = "python3 {hook_script_path}"
     let second_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "second turn".to_string(),
                 text_elements: Vec::new(),
@@ -792,6 +794,7 @@ command = "python3 {hook_script_path}"
     let third_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "third turn".to_string(),
                 text_elements: Vec::new(),
@@ -932,6 +935,7 @@ command = "python3 {hook_script_path}"
     let first_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "first turn".to_string(),
                 text_elements: Vec::new(),
@@ -983,6 +987,7 @@ command = "python3 {hook_script_path}"
     let second_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "second turn".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/initialize.rs

@@ -306,6 +306,7 @@ async fn turn_start_notify_payload_includes_initialize_client_name() -> Result<(
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/mcp_server_elicitation.rs

@@ -135,6 +135,7 @@ async fn mcp_server_elicitation_round_trip() -> Result<()> {
     let warmup_turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Warm up connectors.".to_string(),
                 text_elements: Vec::new(),
@@ -167,6 +168,7 @@ async fn mcp_server_elicitation_round_trip() -> Result<()> {
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Use [$calendar](app://calendar) to run the calendar tool.".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/mcp_tool.rs

@@ -461,6 +461,7 @@ url = "{mcp_server_url}/mcp"
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Call the large MCP tool".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/output_schema.rs

@@ -59,6 +59,7 @@ async fn turn_start_accepts_output_schema_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -141,6 +142,7 @@ async fn turn_start_output_schema_is_per_turn_v2() -> Result<()> {
     let turn_req_1 = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -183,6 +185,7 @@ async fn turn_start_output_schema_is_per_turn_v2() -> Result<()> {
     let turn_req_2 = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello again".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/plan_item.rs

@@ -152,6 +152,7 @@ async fn start_plan_mode_turn(mcp: &mut McpProcess) -> Result<codex_app_server_p
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Plan this".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/remote_thread_store.rs

@@ -113,6 +113,7 @@ async fn thread_start_with_non_local_thread_store_does_not_create_local_persiste
             request_id: RequestId::Integer(2),
             params: TurnStartParams {
                 thread_id: thread.id.clone(),
+                client_user_message_id: None,
                 input: vec![V2UserInput::Text {
                     text: "Hello".to_string(),
                     text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/request_permissions.rs

@@ -49,6 +49,7 @@ async fn request_permissions_round_trip() -> Result<()> {
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "pick a directory".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/request_user_input.rs

@@ -51,6 +51,7 @@ async fn request_user_input_round_trip() -> Result<()> {
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "ask something".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/review.rs

@@ -91,6 +91,7 @@ async fn review_start_runs_review_turn_and_emits_code_review_item() -> Result<()
         turn.items,
         vec![ThreadItem::UserMessage {
             id: turn_id.clone(),
+            client_id: None,
             content: vec![V2UserInput::Text {
                 text: "commit 1234567: Tidy UI colors".to_string(),
                 text_elements: Vec::new(),
@@ -199,6 +200,7 @@ async fn review_start_exec_approval_item_id_matches_command_execution_item() ->
         turn.items,
         vec![ThreadItem::UserMessage {
             id: turn_id.clone(),
+            client_id: None,
             content: vec![V2UserInput::Text {
                 text: "commit 1234567: Check review approvals".to_string(),
                 text_elements: Vec::new(),
@@ -328,6 +330,7 @@ async fn review_start_with_detached_delivery_returns_new_thread_id() -> Result<(
         turn.items,
         vec![ThreadItem::UserMessage {
             id: turn.id.clone(),
+            client_id: None,
             content: vec![V2UserInput::Text {
                 text: "detached review".to_string(),
                 text_elements: Vec::new(),
@@ -465,6 +468,7 @@ async fn materialize_thread_rollout(mcp: &mut McpProcess, thread_id: &str) -> Re
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.to_string(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "materialize rollout".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/safety_check_downgrade.rs

@@ -67,6 +67,7 @@ async fn openai_model_header_mismatch_emits_model_rerouted_notification_v2() ->
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "trigger safeguard".to_string(),
                 text_elements: Vec::new(),
@@ -133,6 +134,7 @@ async fn cyber_policy_response_emits_typed_error_notification_v2() -> Result<()>
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "trigger cyber policy error".to_string(),
                 text_elements: Vec::new(),
@@ -209,6 +211,7 @@ async fn response_model_field_mismatch_emits_model_rerouted_notification_v2_when
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "trigger response model check".to_string(),
                 text_elements: Vec::new(),
@@ -277,6 +280,7 @@ async fn model_verification_emits_typed_notification_and_warning_v2() -> Result<
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "trigger model verification".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_archive.rs

@@ -93,6 +93,7 @@ async fn thread_archive_requires_materialized_rollout() -> Result<()> {
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize".to_string(),
                 text_elements: Vec::new(),
@@ -517,6 +518,7 @@ async fn thread_archive_clears_stale_subscriptions_before_resume() -> Result<()>
     let turn_start_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize".to_string(),
                 text_elements: Vec::new(),
@@ -594,6 +596,7 @@ async fn thread_archive_clears_stale_subscriptions_before_resume() -> Result<()>
     let resumed_turn_id = secondary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "secondary turn".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_fork.rs

@@ -747,6 +747,7 @@ async fn thread_fork_ephemeral_remains_pathless_and_omits_listing() -> Result<()
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: fork_thread_id,
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "continue".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_inject_items.rs

@@ -92,6 +92,7 @@ async fn thread_inject_items_adds_raw_response_items_to_thread_history() -> Resu
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -170,6 +171,7 @@ async fn thread_inject_items_adds_raw_response_items_after_a_turn() -> Result<()
     let first_turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "First turn".to_string(),
                 text_elements: Vec::new(),
@@ -215,6 +217,7 @@ async fn thread_inject_items_adds_raw_response_items_after_a_turn() -> Result<()
     let second_turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Second turn".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_list.rs

@@ -227,6 +227,7 @@ async fn thread_list_reports_system_error_idle_flag_after_failed_turn() -> Resul
     let seed_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -249,6 +250,7 @@ async fn thread_list_reports_system_error_idle_flag_after_failed_turn() -> Resul
     let failed_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "fail turn".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_read.rs

@@ -1198,6 +1198,7 @@ async fn thread_read_reports_system_error_idle_flag_after_failed_turn() -> Resul
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "fail this turn".to_string(),
                 text_elements: Vec::new(),
@@ -1391,6 +1392,7 @@ async fn seed_pathless_store_thread(
 fn store_history_items() -> Vec<RolloutItem> {
     vec![RolloutItem::EventMsg(EventMsg::UserMessage(
         UserMessageEvent {
+            client_id: None,
             message: "history from store".to_string(),
             images: None,
             local_images: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_resume.rs

@@ -211,6 +211,7 @@ async fn thread_resume_with_empty_path_uses_running_thread_id() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize rollout".to_string(),
                 text_elements: Vec::new(),
@@ -279,6 +280,7 @@ async fn turn_start_updates_runtime_workspace_roots_for_loaded_thread() -> Resul
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -809,6 +811,7 @@ async fn thread_resume_keeps_paused_goal_paused() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize this thread".to_string(),
                 text_elements: Vec::new(),
@@ -913,6 +916,7 @@ async fn thread_goal_set_preserves_budget_limited_same_objective() -> Result<()>
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize this thread".to_string(),
                 text_elements: Vec::new(),
@@ -1011,6 +1015,7 @@ async fn thread_goal_set_persists_resumable_stopped_statuses() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize this thread".to_string(),
                 text_elements: Vec::new(),
@@ -1206,6 +1211,7 @@ async fn thread_goal_clear_deletes_goal_and_notifies() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize this thread".to_string(),
                 text_elements: Vec::new(),
@@ -2074,6 +2080,7 @@ async fn thread_resume_keeps_in_flight_turn_streaming() -> Result<()> {
     let seed_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2099,6 +2106,7 @@ async fn thread_resume_keeps_in_flight_turn_streaming() -> Result<()> {
     let turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "respond with docs".to_string(),
                 text_elements: Vec::new(),
@@ -2181,6 +2189,7 @@ async fn thread_resume_rejects_history_when_thread_is_running() -> Result<()> {
     let seed_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2204,6 +2213,7 @@ async fn thread_resume_rejects_history_when_thread_is_running() -> Result<()> {
     let running_turn_request_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "keep running".to_string(),
                 text_elements: Vec::new(),
@@ -2297,6 +2307,7 @@ async fn thread_resume_rejects_mismatched_path_for_running_thread_id() -> Result
     let seed_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2320,6 +2331,7 @@ async fn thread_resume_rejects_mismatched_path_for_running_thread_id() -> Result
     let running_turn_request_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "keep running".to_string(),
                 text_elements: Vec::new(),
@@ -2433,6 +2445,7 @@ async fn thread_resume_rejoins_running_thread_even_with_override_mismatch() -> R
     let seed_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2455,6 +2468,7 @@ async fn thread_resume_rejoins_running_thread_even_with_override_mismatch() -> R
     let running_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "keep running".to_string(),
                 text_elements: Vec::new(),
@@ -2562,6 +2576,7 @@ async fn thread_resume_can_skip_turns_when_thread_is_running() -> Result<()> {
     let turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2645,6 +2660,7 @@ async fn thread_resume_replays_pending_command_execution_request_approval() -> R
     let seed_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2667,6 +2683,7 @@ async fn thread_resume_replays_pending_command_execution_request_approval() -> R
     let running_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "run command".to_string(),
                 text_elements: Vec::new(),
@@ -2783,6 +2800,7 @@ async fn thread_resume_replays_pending_file_change_request_approval() -> Result<
     let seed_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -2806,6 +2824,7 @@ async fn thread_resume_replays_pending_file_change_request_approval() -> Result<
     let running_turn_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "apply patch".to_string(),
                 text_elements: Vec::new(),
@@ -2950,6 +2969,7 @@ async fn thread_resume_with_overrides_defers_updated_at_until_turn_start() -> Re
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: resumed_thread.id,
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -3262,6 +3282,7 @@ async fn start_materialized_thread_and_restart(
     let materialize_turn_id = first_mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: seed_text.to_string(),
                 text_elements: Vec::new(),
@@ -3351,6 +3372,7 @@ async fn thread_resume_accepts_personality_override() -> Result<()> {
     let materialize_id = primary
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "seed history".to_string(),
                 text_elements: Vec::new(),
@@ -3391,6 +3413,7 @@ async fn thread_resume_accepts_personality_override() -> Result<()> {
     let turn_id = secondary
         .send_turn_start_request(TurnStartParams {
             thread_id: resume.thread.id,
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_rollback.rs

@@ -57,6 +57,7 @@ async fn thread_rollback_drops_last_turns_and_persists_to_rollout() -> Result<()
     let turn1_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: first_text.to_string(),
                 text_elements: Vec::new(),
@@ -78,6 +79,7 @@ async fn thread_rollback_drops_last_turns_and_persists_to_rollout() -> Result<()
     let turn2_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Second".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_settings_update.rs

@@ -259,6 +259,7 @@ async fn turn_start_settings_override_emits_thread_settings_updated() -> Result<
     let turn_request_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "hello".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_shell_command.rs

@@ -275,6 +275,7 @@ async fn thread_shell_command_uses_existing_active_turn() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_status.rs

@@ -48,6 +48,7 @@ async fn thread_status_changed_emits_runtime_updates() -> Result<()> {
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "collect status updates".to_string(),
                 text_elements: Vec::new(),
@@ -171,6 +172,7 @@ async fn thread_status_changed_can_be_opted_out() -> Result<()> {
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run once".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_unarchive.rs

@@ -81,6 +81,7 @@ async fn thread_unarchive_moves_rollout_back_into_sessions_directory() -> Result
     let turn_start_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![UserInput::Text {
                 text: "materialize".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/thread_unsubscribe.rs

@@ -151,6 +151,7 @@ async fn thread_unsubscribe_during_turn_keeps_turn_running() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run deterministic tool".to_string(),
                 text_elements: Vec::new(),
@@ -260,6 +261,7 @@ async fn thread_unsubscribe_preserves_cached_status_before_idle_unload() -> Resu
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread_id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "fail this turn".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/turn_interrupt.rs

@@ -78,6 +78,7 @@ async fn turn_interrupt_aborts_running_turn() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run sleep".to_string(),
                 text_elements: Vec::new(),
@@ -159,6 +160,7 @@ async fn turn_interrupt_rejects_completed_turn() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "say done".to_string(),
                 text_elements: Vec::new(),
@@ -253,6 +255,7 @@ async fn turn_interrupt_resolves_pending_command_approval_request() -> Result<()
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/turn_start.rs

@@ -141,6 +141,7 @@ async fn run_local_image_turn(detail: Option<ImageDetail>) -> Result<Vec<Value>>
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::LocalImage {
                 path: image_path,
                 detail,
@@ -235,6 +236,7 @@ async fn turn_start_with_empty_input_runs_model_request() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: Vec::new(),
             ..Default::default()
         })
@@ -335,6 +337,7 @@ async fn turn_start_additional_context_flows_to_model_input() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "inspect tab".to_string(),
                 text_elements: Vec::new(),
@@ -420,6 +423,7 @@ async fn turn_start_sends_originator_header() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -492,6 +496,7 @@ async fn turn_start_emits_user_message_item_with_text_elements() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: Some("client-message-1".to_string()),
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: text_elements.clone(),
@@ -521,7 +526,10 @@ async fn turn_start_emits_user_message_item_with_text_elements() -> Result<()> {
     .await??;
 
     match user_message_item {
-        ThreadItem::UserMessage { content, .. } => {
+        ThreadItem::UserMessage {
+            client_id, content, ..
+        } => {
+            assert_eq!(client_id, Some("client-message-1".to_string()));
             assert_eq!(
                 content,
                 vec![V2UserInput::Text {
@@ -595,6 +603,7 @@ async fn turn_start_emits_thread_scoped_warning_notification_for_trimmed_skills(
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -761,6 +770,7 @@ async fn thread_start_omits_empty_instruction_overrides_from_model_request() ->
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -840,6 +850,7 @@ async fn turn_start_tracks_turn_event_analytics() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Image {
                 url: "https://example.com/a.png".to_string(),
                 detail: None,
@@ -928,6 +939,7 @@ async fn turn_start_accepts_text_at_limit_with_mention_item() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![
                 V2UserInput::Text {
                     text: "x".repeat(MAX_USER_INPUT_TEXT_CHARS),
@@ -991,6 +1003,7 @@ async fn turn_start_rejects_combined_oversized_text_input() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![
                 V2UserInput::Text {
                     text: first,
@@ -1065,6 +1078,7 @@ async fn turn_start_rejects_invalid_permission_selection_before_starting_turn()
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1137,6 +1151,7 @@ async fn turn_start_rejects_unknown_environment_before_starting_turn() -> Result
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1210,6 +1225,7 @@ async fn turn_start_emits_notifications_and_accepts_model_override() -> Result<(
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1262,6 +1278,7 @@ async fn turn_start_emits_notifications_and_accepts_model_override() -> Result<(
     let turn_req2 = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Second".to_string(),
                 text_elements: Vec::new(),
@@ -1360,6 +1377,7 @@ async fn turn_start_accepts_collaboration_mode_override_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1449,6 +1467,7 @@ async fn turn_start_uses_thread_feature_overrides_for_request_user_input_tool_de
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1520,6 +1539,7 @@ async fn turn_start_accepts_personality_override_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1601,6 +1621,7 @@ async fn turn_start_change_personality_mid_thread_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1625,6 +1646,7 @@ async fn turn_start_change_personality_mid_thread_v2() -> Result<()> {
     let turn_req2 = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello again".to_string(),
                 text_elements: Vec::new(),
@@ -1727,6 +1749,7 @@ async fn turn_start_uses_migrated_pragmatic_personality_without_override_v2() ->
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Hello".to_string(),
                 text_elements: Vec::new(),
@@ -1847,6 +1870,7 @@ async fn turn_start_exec_approval_toggle_v2() -> Result<()> {
     let first_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python".to_string(),
                 text_elements: Vec::new(),
@@ -1911,6 +1935,7 @@ async fn turn_start_exec_approval_toggle_v2() -> Result<()> {
     let second_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python again".to_string(),
                 text_elements: Vec::new(),
@@ -1988,6 +2013,7 @@ async fn turn_start_exec_approval_decline_v2() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python".to_string(),
                 text_elements: Vec::new(),
@@ -2143,6 +2169,7 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
         .send_turn_start_request(TurnStartParams {
             environments: None,
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "first turn".to_string(),
                 text_elements: Vec::new(),
@@ -2186,6 +2213,7 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
         .send_turn_start_request(TurnStartParams {
             environments: None,
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "second turn".to_string(),
                 text_elements: Vec::new(),
@@ -2328,6 +2356,7 @@ stream_max_retries = 0
     let first_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "select dev profile".to_string(),
                 text_elements: Vec::new(),
@@ -2351,6 +2380,7 @@ stream_max_retries = 0
     let second_turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "write in new root".to_string(),
                 text_elements: Vec::new(),
@@ -2483,6 +2513,7 @@ async fn run_environment_selection_case(
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: format!("run {}", case.name),
                 text_elements: Vec::new(),
@@ -2598,6 +2629,7 @@ async fn turn_start_file_change_approval_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "apply patch".into(),
                 text_elements: Vec::new(),
@@ -2788,6 +2820,7 @@ async fn turn_start_does_not_stream_apply_patch_change_updates_without_feature_v
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "apply patch".into(),
                 text_elements: Vec::new(),
@@ -2925,6 +2958,7 @@ async fn turn_start_streams_apply_patch_change_updates_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "apply patch".into(),
                 text_elements: Vec::new(),
@@ -3055,6 +3089,7 @@ async fn turn_start_emits_spawn_agent_item_with_model_metadata_v2() -> Result<()
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: PARENT_PROMPT.to_string(),
                 text_elements: Vec::new(),
@@ -3274,6 +3309,7 @@ config_file = "./custom-role.toml"
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: PARENT_PROMPT.to_string(),
                 text_elements: Vec::new(),
@@ -3419,6 +3455,7 @@ async fn turn_start_file_change_approval_accept_for_session_persists_v2() -> Res
     let turn_1_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "apply patch 1".into(),
                 text_elements: Vec::new(),
@@ -3491,6 +3528,7 @@ async fn turn_start_file_change_approval_accept_for_session_persists_v2() -> Res
     let turn_2_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "apply patch 2".into(),
                 text_elements: Vec::new(),
@@ -3589,6 +3627,7 @@ async fn turn_start_file_change_approval_decline_v2() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "apply patch".into(),
                 text_elements: Vec::new(),
@@ -3734,6 +3773,7 @@ async fn command_execution_notifications_include_process_id() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run a command".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/turn_start_zsh_fork.rs

@@ -117,6 +117,7 @@ async fn turn_start_shell_zsh_fork_executes_command_v2() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run echo hi".to_string(),
                 text_elements: Vec::new(),
@@ -235,6 +236,7 @@ async fn turn_start_shell_zsh_fork_exec_approval_decline_v2() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python".to_string(),
                 text_elements: Vec::new(),
@@ -367,6 +369,7 @@ async fn turn_start_shell_zsh_fork_exec_approval_cancel_v2() -> Result<()> {
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run python".to_string(),
                 text_elements: Vec::new(),
@@ -525,6 +528,7 @@ async fn turn_start_shell_zsh_fork_subcommand_decline_marks_parent_declined_v2()
     let turn_id = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "remove both files".to_string(),
                 text_elements: Vec::new(),

codex-rs/app-server/tests/suite/v2/turn_steer.rs

@@ -12,10 +12,12 @@ use codex_app_server::INPUT_TOO_LARGE_ERROR_CODE;
 use codex_app_server::INVALID_PARAMS_ERROR_CODE;
 use codex_app_server_protocol::AdditionalContextEntry;
 use codex_app_server_protocol::AdditionalContextKind;
+use codex_app_server_protocol::ItemStartedNotification;
 use codex_app_server_protocol::JSONRPCError;
 use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::RequestId;
+use codex_app_server_protocol::ThreadItem;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
 use codex_app_server_protocol::TurnStartParams;
@@ -67,6 +69,7 @@ async fn turn_steer_requires_active_turn() -> Result<()> {
     let steer_req = mcp
         .send_turn_steer_request(TurnSteerParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: Some("client-steer-message-1".to_string()),
             input: vec![V2UserInput::Text {
                 text: "steer".to_string(),
                 text_elements: Vec::new(),
@@ -152,6 +155,7 @@ async fn turn_steer_rejects_oversized_text_input() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run sleep".to_string(),
                 text_elements: Vec::new(),
@@ -177,6 +181,7 @@ async fn turn_steer_rejects_oversized_text_input() -> Result<()> {
     let steer_req = mcp
         .send_turn_steer_request(TurnSteerParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: oversized_input.clone(),
                 text_elements: Vec::new(),
@@ -217,10 +222,10 @@ async fn turn_steer_returns_active_turn_id() -> Result<()> {
     let shell_command = vec![
         "powershell".to_string(),
         "-Command".to_string(),
-        "Start-Sleep -Seconds 10".to_string(),
+        "Start-Sleep -Seconds 2".to_string(),
     ];
     #[cfg(not(target_os = "windows"))]
-    let shell_command = vec!["sleep".to_string(), "10".to_string()];
+    let shell_command = vec!["sleep".to_string(), "2".to_string()];
 
     let tmp = TempDir::new()?;
     let codex_home = tmp.path().join("codex_home");
@@ -228,14 +233,16 @@ async fn turn_steer_returns_active_turn_id() -> Result<()> {
     let working_directory = tmp.path().join("workdir");
     std::fs::create_dir(&working_directory)?;
 
-    let server =
-        create_mock_responses_server_sequence_unchecked(vec![create_shell_command_sse_response(
+    let server = create_mock_responses_server_sequence_unchecked(vec![
+        create_shell_command_sse_response(
             shell_command.clone(),
             Some(&working_directory),
             Some(10_000),
             "call_sleep",
-        )?])
-        .await;
+        )?,
+        app_test_support::create_final_assistant_message_sse_response("Done")?,
+    ])
+    .await;
     write_mock_responses_config_toml_with_chatgpt_base_url(
         &codex_home,
         &server.uri(),
@@ -262,6 +269,7 @@ async fn turn_steer_returns_active_turn_id() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run sleep".to_string(),
                 text_elements: Vec::new(),
@@ -286,6 +294,7 @@ async fn turn_steer_returns_active_turn_id() -> Result<()> {
     let steer_req = mcp
         .send_turn_steer_request(TurnSteerParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: Some("client-steer-message-1".to_string()),
             input: vec![V2UserInput::Text {
                 text: "steer".to_string(),
                 text_elements: Vec::new(),
@@ -303,6 +312,34 @@ async fn turn_steer_returns_active_turn_id() -> Result<()> {
     let steer: TurnSteerResponse = to_response::<TurnSteerResponse>(steer_resp)?;
     assert_eq!(steer.turn_id, turn.id);
 
+    timeout(DEFAULT_READ_TIMEOUT, async {
+        loop {
+            let notification = mcp
+                .read_stream_until_notification_message("item/started")
+                .await?;
+            let params = notification.params.expect("item/started params");
+            let item_started: ItemStartedNotification =
+                serde_json::from_value(params).expect("deserialize item/started notification");
+            let ThreadItem::UserMessage {
+                client_id, content, ..
+            } = item_started.item
+            else {
+                continue;
+            };
+            if client_id == Some("client-steer-message-1".to_string()) {
+                assert_eq!(
+                    content,
+                    vec![V2UserInput::Text {
+                        text: "steer".to_string(),
+                        text_elements: Vec::new(),
+                    }]
+                );
+                return Ok::<(), anyhow::Error>(());
+            }
+        }
+    })
+    .await??;
+
     let event =
         wait_for_analytics_event(&server, DEFAULT_READ_TIMEOUT, "codex_turn_steer_event").await?;
     assert_eq!(event["event_params"]["thread_id"], thread.id);
@@ -316,8 +353,11 @@ async fn turn_steer_returns_active_turn_id() -> Result<()> {
         serde_json::Value::Null
     );
 
-    mcp.interrupt_turn_and_wait_for_aborted(thread.id, steer.turn_id, DEFAULT_READ_TIMEOUT)
-        .await?;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
 
     Ok(())
 }
@@ -366,6 +406,7 @@ async fn turn_steer_rejects_context_only_input_without_merging_context() -> Resu
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "run sleep".to_string(),
                 text_elements: Vec::new(),
@@ -396,6 +437,7 @@ async fn turn_steer_rejects_context_only_input_without_merging_context() -> Resu
     let steer_req = mcp
         .send_turn_steer_request(TurnSteerParams {
             thread_id: thread.id.clone(),
+            client_user_message_id: None,
             input: Vec::new(),
             responsesapi_client_metadata: None,
             additional_context,

codex-rs/app-server/tests/suite/v2/web_search.rs

@@ -88,6 +88,7 @@ async fn standalone_web_search_round_trips_encrypted_output() -> Result<()> {
     let turn_req = mcp
         .send_turn_start_request(TurnStartParams {
             thread_id: thread.id,
+            client_user_message_id: None,
             input: vec![V2UserInput::Text {
                 text: "Search the web".to_string(),
                 text_elements: Vec::new(),

codex-rs/core-skills/src/injection.rs

@@ -132,7 +132,7 @@ pub fn collect_explicit_skill_mentions(
     let mut blocked_plain_names: HashSet<String> = HashSet::new();
 
     for input in inputs {
-        if let UserInput::Skill { name, path } = input {
+        if let UserInput::Skill { name, path, .. } = input {
             blocked_plain_names.insert(name.clone());
             let Ok(path) = AbsolutePathBuf::relative_to_current_dir(path) else {
                 continue;

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

@@ -1296,8 +1296,10 @@ pub(crate) fn render_input_preview(initial_operation: &Op) -> String {
                 UserInput::LocalImage { path, .. } => {
                     format!("[local_image:{}]", path.display())
                 }
-                UserInput::Skill { name, path } => format!("[skill:${name}]({})", path.display()),
-                UserInput::Mention { name, path } => format!("[mention:${name}]({path})"),
+                UserInput::Skill { name, path, .. } => {
+                    format!("[skill:${name}]({})", path.display())
+                }
+                UserInput::Mention { name, path, .. } => format!("[mention:${name}]({path})"),
                 _ => "[input]".to_string(),
             })
             .collect::<Vec<_>>()

codex-rs/core/src/codex_delegate.rs

@@ -218,6 +218,7 @@ pub(crate) async fn run_codex_thread_one_shot(
                     .send(Submission {
                         id: "shutdown".to_string(),
                         op: Op::Shutdown {},
+                        client_user_message_id: None,
                         trace: None,
                     })
                     .await;

codex-rs/core/src/codex_delegate_tests.rs

@@ -129,6 +129,7 @@ async fn forward_ops_preserves_submission_trace_context() {
     let submission = Submission {
         id: "sub-1".to_string(),
         op: Op::Interrupt,
+        client_user_message_id: None,
         trace: Some(codex_protocol::protocol::W3cTraceContext {
             traceparent: Some(
                 "00-1234567890abcdef1234567890abcdef-1234567890abcdef-01".to_string(),

codex-rs/core/src/codex_thread.rs

@@ -230,6 +230,17 @@ impl CodexThread {
         self.codex.submit_with_trace(op, trace).await
     }
 
+    pub async fn submit_user_input_with_client_user_message_id(
+        &self,
+        op: Op,
+        trace: Option<W3cTraceContext>,
+        client_user_message_id: Option<String>,
+    ) -> CodexResult<String> {
+        self.codex
+            .submit_user_input_with_client_user_message_id(op, trace, client_user_message_id)
+            .await
+    }
+
     /// Persist whether this thread is eligible for future memory generation.
     pub async fn set_thread_memory_mode(&self, mode: ThreadMemoryMode) -> anyhow::Result<()> {
         self.codex.set_thread_memory_mode(mode).await
@@ -240,6 +251,7 @@ impl CodexThread {
         input: Vec<UserInput>,
         additional_context: BTreeMap<String, AdditionalContextEntry>,
         expected_turn_id: Option<&str>,
+        client_user_message_id: Option<String>,
         responsesapi_client_metadata: Option<HashMap<String, String>>,
     ) -> Result<String, SteerInputError> {
         self.codex
@@ -247,6 +259,7 @@ impl CodexThread {
                 input,
                 additional_context,
                 expected_turn_id,
+                client_user_message_id,
                 responsesapi_client_metadata,
             )
             .await

codex-rs/core/src/hook_runtime.rs

@@ -500,7 +500,7 @@ pub(crate) async fn inspect_pending_input(
     pending_input_item: &TurnInput,
 ) -> HookRuntimeOutcome {
     match pending_input_item {
-        TurnInput::UserInput(content) => {
+        TurnInput::UserInput { content, .. } => {
             let request = UserPromptSubmitRequest {
                 session_id: sess.session_id().into(),
                 turn_id: turn_context.sub_id.clone(),
@@ -536,9 +536,13 @@ pub(crate) async fn record_pending_input(
     additional_contexts: Vec<String>,
 ) {
     match pending_input {
-        TurnInput::UserInput(content) => {
-            sess.record_user_prompt_and_emit_turn_item(turn_context.as_ref(), content.as_slice())
-                .await;
+        TurnInput::UserInput { content, client_id } => {
+            sess.record_user_prompt_and_emit_turn_item(
+                turn_context.as_ref(),
+                content.as_slice(),
+                client_id,
+            )
+            .await;
         }
         TurnInput::ResponseItem(item) => {
             sess.record_conversation_items(turn_context, std::slice::from_ref(&item))

codex-rs/core/src/personality_migration_tests.rs

@@ -68,6 +68,7 @@ async fn write_rollout_with_user_event(dir: &Path, thread_id: ThreadId) -> io::R
     let user_event = RolloutLine {
         timestamp: TEST_TIMESTAMP.to_string(),
         item: RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "hello".to_string(),
             images: None,
             local_images: Vec::new(),

codex-rs/core/src/session/handlers.rs

@@ -85,12 +85,18 @@ pub async fn realtime_conversation_list_voices(sess: &Session, sub_id: String) {
     .await;
 }
 
-pub async fn user_input_or_turn(sess: &Arc<Session>, sub_id: String, op: Op) {
+pub async fn user_input_or_turn(
+    sess: &Arc<Session>,
+    sub_id: String,
+    op: Op,
+    client_user_message_id: Option<String>,
+) {
     user_input_or_turn_inner(
         sess,
         sub_id,
         op,
         /*mirror_user_text_to_realtime*/ Some(()),
+        client_user_message_id,
     )
     .await;
 }
@@ -190,6 +196,7 @@ pub(super) async fn user_input_or_turn_inner(
     sub_id: String,
     op: Op,
     mirror_user_text_to_realtime: Option<()>,
+    client_user_message_id: Option<String>,
 ) {
     let Op::UserInput {
         items,
@@ -229,6 +236,7 @@ pub(super) async fn user_input_or_turn_inner(
             items.clone(),
             additional_context.clone(),
             /*expected_turn_id*/ None,
+            client_user_message_id.clone(),
             responsesapi_client_metadata.clone(),
         )
         .await
@@ -260,7 +268,10 @@ pub(super) async fn user_input_or_turn_inner(
                 .map(TurnInput::ResponseItem)
                 .collect::<Vec<_>>();
             if !items.is_empty() {
-                task_input.push(TurnInput::UserInput(items));
+                task_input.push(TurnInput::UserInput {
+                    content: items,
+                    client_id: client_user_message_id,
+                });
             }
             sess.spawn_task(
                 Arc::clone(&current_context),
@@ -773,7 +784,8 @@ pub(super) async fn submission_loop(
                     false
                 }
                 Op::UserInput { .. } => {
-                    user_input_or_turn(&sess, sub.id.clone(), sub.op).await;
+                    user_input_or_turn(&sess, sub.id.clone(), sub.op, sub.client_user_message_id)
+                        .await;
                     false
                 }
                 Op::ThreadSettings { thread_settings } => {

codex-rs/core/src/session/input_queue.rs

@@ -11,7 +11,10 @@ use tokio::sync::watch;
 
 #[derive(Clone, Debug, PartialEq)]
 pub(crate) enum TurnInput {
-    UserInput(Vec<UserInput>),
+    UserInput {
+        content: Vec<UserInput>,
+        client_id: Option<String>,
+    },
     ResponseItem(ResponseItem),
 }
 

codex-rs/core/src/session/mod.rs

@@ -667,6 +667,25 @@ impl Codex {
         let sub = Submission {
             id: id.clone(),
             op,
+            client_user_message_id: None,
+            trace,
+        };
+        self.submit_with_id(sub).await?;
+        Ok(id)
+    }
+
+    pub async fn submit_user_input_with_client_user_message_id(
+        &self,
+        op: Op,
+        trace: Option<W3cTraceContext>,
+        client_user_message_id: Option<String>,
+    ) -> CodexResult<String> {
+        debug_assert!(matches!(op, Op::UserInput { .. }));
+        let id = Uuid::now_v7().to_string();
+        let sub = Submission {
+            id: id.clone(),
+            op,
+            client_user_message_id,
             trace,
         };
         self.submit_with_id(sub).await?;
@@ -722,6 +741,7 @@ impl Codex {
         input: Vec<UserInput>,
         additional_context: BTreeMap<String, AdditionalContextEntry>,
         expected_turn_id: Option<&str>,
+        client_user_message_id: Option<String>,
         responsesapi_client_metadata: Option<HashMap<String, String>>,
     ) -> Result<String, SteerInputError> {
         self.session
@@ -729,6 +749,7 @@ impl Codex {
                 input,
                 additional_context,
                 expected_turn_id,
+                client_user_message_id,
                 responsesapi_client_metadata,
             )
             .await
@@ -1074,6 +1095,7 @@ impl Session {
                 thread_settings: Default::default(),
             },
             /*mirror_user_text_to_realtime*/ None,
+            /*client_user_message_id*/ None,
         )
         .await;
     }
@@ -3056,6 +3078,7 @@ impl Session {
         &self,
         turn_context: &TurnContext,
         input: &[UserInput],
+        client_id: Option<String>,
     ) {
         // Persist the user message to history, but emit the turn item from `UserInput` so
         // UI-only `text_elements` are preserved. `ResponseItem::Message` does not carry
@@ -3063,7 +3086,9 @@ impl Session {
         let response_item = ResponseItem::from(ResponseInputItem::from(input.to_vec()));
         self.record_conversation_items(turn_context, std::slice::from_ref(&response_item))
             .await;
-        let turn_item = TurnItem::UserMessage(UserMessageItem::new(input));
+        let mut user_message_item = UserMessageItem::new(input);
+        user_message_item.client_id = client_id;
+        let turn_item = TurnItem::UserMessage(user_message_item);
         self.emit_turn_item_started(turn_context, &turn_item).await;
         self.emit_turn_item_completed(turn_context, turn_item).await;
         self.ensure_rollout_materialized().await;
@@ -3099,6 +3124,7 @@ impl Session {
         input: Vec<UserInput>,
         additional_context: BTreeMap<String, AdditionalContextEntry>,
         expected_turn_id: Option<&str>,
+        client_user_message_id: Option<String>,
         responsesapi_client_metadata: Option<HashMap<String, String>>,
     ) -> Result<String, SteerInputError> {
         let mut active = self.active_turn.lock().await;
@@ -3155,7 +3181,10 @@ impl Session {
             .map(ResponseItem::from)
             .map(TurnInput::ResponseItem)
             .collect::<Vec<_>>();
-        pending_input.push(TurnInput::UserInput(input));
+        pending_input.push(TurnInput::UserInput {
+            content: input,
+            client_id: client_user_message_id,
+        });
         self.input_queue
             .extend_pending_input_and_accept_mailbox_delivery_for_turn_state(
                 active_turn.turn_state.as_ref(),

codex-rs/core/src/session/review.rs

@@ -137,11 +137,14 @@ pub(super) async fn spawn_review_thread(
     };
 
     // Seed the child task with the review prompt as the initial user message.
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: review_prompt,
-        // Review prompt is synthesized; no UI element ranges to preserve.
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: review_prompt,
+            // Review prompt is synthesized; no UI element ranges to preserve.
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     let tc = Arc::new(review_turn_context);
     tc.turn_metadata_state.spawn_git_enrichment_task();
     // TODO(ccunningham): Review turns currently rely on `spawn_task` for TurnComplete but do not

codex-rs/core/src/session/rollout_reconstruction_tests.rs

@@ -130,6 +130,7 @@ async fn record_initial_history_resumed_hydrates_previous_turn_settings_from_lif
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -198,6 +199,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_com
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 1 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -228,6 +230,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_com
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 2 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -300,6 +303,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_inc
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 1 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -330,6 +334,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_inc
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 2 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -394,6 +399,7 @@ async fn reconstruct_history_rollback_skips_non_user_turns_for_history_and_metad
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 1 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -424,6 +430,7 @@ async fn reconstruct_history_rollback_skips_non_user_turns_for_history_and_metad
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 2 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -517,6 +524,7 @@ async fn reconstruct_history_rollback_counts_inter_agent_assistant_turns() {
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 1 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -608,6 +616,7 @@ async fn reconstruct_history_rollback_clears_history_and_metadata_when_exceeding
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "only user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -662,6 +671,7 @@ async fn record_initial_history_resumed_rollback_skips_only_user_turns() {
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -737,6 +747,7 @@ async fn record_initial_history_resumed_rollback_drops_incomplete_user_turn_comp
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -765,6 +776,7 @@ async fn record_initial_history_resumed_rollback_drops_incomplete_user_turn_comp
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "rolled back".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -898,6 +910,7 @@ async fn reconstruct_history_legacy_compaction_without_replacement_history_clear
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "after legacy compact".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -963,6 +976,7 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1068,6 +1082,7 @@ async fn record_initial_history_resumed_aborted_turn_without_id_clears_active_tu
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1096,6 +1111,7 @@ async fn record_initial_history_resumed_aborted_turn_without_id_clears_active_tu
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "aborted".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1178,6 +1194,7 @@ async fn record_initial_history_resumed_unmatched_abort_preserves_active_turn_fo
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1206,6 +1223,7 @@ async fn record_initial_history_resumed_unmatched_abort_preserves_active_turn_fo
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "current".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1297,6 +1315,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_compaction_clea
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1325,6 +1344,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_compaction_clea
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "incomplete".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1377,6 +1397,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_preserves_turn_
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "incomplete".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1452,6 +1473,7 @@ async fn record_initial_history_resumed_replaced_incomplete_compacted_turn_clear
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -1480,6 +1502,7 @@ async fn record_initial_history_resumed_replaced_incomplete_compacted_turn_clear
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "compacted".to_string(),
                 images: None,
                 local_images: Vec::new(),

codex-rs/core/src/session/tests.rs

@@ -2490,6 +2490,7 @@ async fn record_initial_history_forked_hydrates_previous_turn_settings() {
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "forked seed".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -2686,6 +2687,7 @@ async fn thread_rollback_recomputes_previous_turn_settings_and_reference_context
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 1 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -2714,6 +2716,7 @@ async fn thread_rollback_recomputes_previous_turn_settings_and_reference_context
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(
             codex_protocol::protocol::UserMessageEvent {
+                client_id: None,
                 message: "turn 2 user".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -2798,6 +2801,7 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
             },
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "turn 1 user".to_string(),
             images: None,
             local_images: Vec::new(),
@@ -2844,6 +2848,7 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
             },
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "turn 2 user".to_string(),
             images: None,
             local_images: Vec::new(),
@@ -2900,6 +2905,7 @@ async fn thread_rollback_persists_marker_and_replays_cumulatively() {
             },
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "turn 1 user".to_string(),
             images: None,
             local_images: Vec::new(),
@@ -2926,6 +2932,7 @@ async fn thread_rollback_persists_marker_and_replays_cumulatively() {
             },
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "turn 2 user".to_string(),
             images: None,
             local_images: Vec::new(),
@@ -2952,6 +2959,7 @@ async fn thread_rollback_persists_marker_and_replays_cumulatively() {
             },
         )),
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "turn 3 user".to_string(),
             images: None,
             local_images: Vec::new(),
@@ -5410,6 +5418,7 @@ async fn submit_with_id_captures_current_span_trace_context() {
             .submit_with_id(Submission {
                 id: "sub-1".into(),
                 op: Op::Interrupt,
+                client_user_message_id: None,
                 trace: None,
             })
             .await
@@ -5481,6 +5490,7 @@ fn submission_dispatch_span_prefers_submission_trace_context() {
         submission_dispatch_span(&Submission {
             id: "sub-1".into(),
             op: Op::Interrupt,
+            client_user_message_id: None,
             trace: Some(submission_trace),
         })
     });
@@ -5507,6 +5517,7 @@ fn submission_dispatch_span_uses_debug_for_realtime_audio() {
                 item_id: None,
             },
         }),
+        client_user_message_id: None,
         trace: None,
     });
 
@@ -5574,6 +5585,7 @@ async fn user_turn_updates_approvals_reviewer() {
                 ..Default::default()
             },
         },
+        /*client_user_message_id*/ None,
     )
     .await;
 
@@ -5867,6 +5879,7 @@ async fn spawn_task_turn_span_inherits_dispatch_trace_context() {
     let dispatch_span = submission_dispatch_span(&Submission {
         id: "sub-1".into(),
         op: Op::Interrupt,
+        client_user_message_id: None,
         trace: Some(submission_trace.clone()),
     });
     let dispatch_span_id = dispatch_span.context().span().span_context().span_id();
@@ -5877,10 +5890,13 @@ async fn spawn_task_turn_span_inherits_dispatch_trace_context() {
     async {
         sess.spawn_task(
             Arc::clone(&tc),
-            vec![TurnInput::UserInput(vec![UserInput::Text {
-                text: "hello".to_string(),
-                text_elements: Vec::new(),
-            }])],
+            vec![TurnInput::UserInput {
+                content: vec![UserInput::Text {
+                    text: "hello".to_string(),
+                    text_elements: Vec::new(),
+                }],
+                client_id: None,
+            }],
             TraceCaptureTask {
                 captured_trace: Arc::clone(&captured_trace),
             },
@@ -6689,10 +6705,13 @@ async fn spawn_task_does_not_update_previous_turn_settings_for_non_run_turn_task
     let (sess, tc, _rx) = make_session_and_context_with_rx().await;
     sess.set_previous_turn_settings(/*previous_turn_settings*/ None)
         .await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "hello".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "hello".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
 
     sess.spawn_task(
         Arc::clone(&tc),
@@ -7775,6 +7794,7 @@ async fn record_context_updates_and_set_reference_context_item_persists_full_rei
     session
         .persist_rollout_items(&[RolloutItem::EventMsg(EventMsg::UserMessage(
             UserMessageEvent {
+                client_id: None,
                 message: "seed rollout".to_string(),
                 images: None,
                 local_images: Vec::new(),
@@ -7981,10 +8001,13 @@ impl SessionTask for GuardianDeniedApprovalTask {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn guardian_auto_review_interrupts_after_three_consecutive_denials() {
     let (sess, tc, rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "trigger guardian denials".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "trigger guardian denials".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(Arc::clone(&tc), input, GuardianDeniedApprovalTask)
         .await;
 
@@ -8012,10 +8035,13 @@ async fn guardian_auto_review_interrupts_after_three_consecutive_denials() {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn guardian_helper_review_interrupts_after_three_consecutive_denials() {
     let (sess, tc, rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "keep turn active for helper reviews".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "keep turn active for helper reviews".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(
         Arc::clone(&tc),
         input,
@@ -8072,10 +8098,13 @@ async fn guardian_helper_review_interrupts_after_three_consecutive_denials() {
 #[test_log::test]
 async fn abort_regular_task_emits_marker_before_turn_aborted() {
     let (sess, tc, rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "hello".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "hello".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(
         Arc::clone(&tc),
         input,
@@ -8110,10 +8139,13 @@ async fn abort_regular_task_emits_marker_before_turn_aborted() {
 #[tokio::test]
 async fn abort_gracefully_emits_marker_before_turn_aborted() {
     let (sess, tc, rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "hello".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "hello".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(
         Arc::clone(&tc),
         input,
@@ -8148,10 +8180,13 @@ async fn abort_gracefully_emits_marker_before_turn_aborted() {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn task_finish_emits_turn_item_lifecycle_for_leftover_pending_user_input() {
     let (sess, tc, rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "hello".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "hello".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(
         Arc::clone(&tc),
         input,
@@ -8176,6 +8211,7 @@ async fn task_finish_emits_turn_item_lifecycle_for_leftover_pending_user_input()
         pending_user_input.clone(),
         /*additional_context*/ Default::default(),
         Some(&tc.sub_id),
+        /*client_user_message_id*/ None,
         /*responsesapi_client_metadata*/ None,
     )
     .await
@@ -8235,6 +8271,7 @@ async fn task_finish_emits_turn_item_lifecycle_for_leftover_pending_user_input()
     assert!(matches!(
         fourth.msg,
         EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
             message,
             images,
             text_elements,
@@ -8354,6 +8391,7 @@ async fn steer_input_requires_active_turn() {
             input,
             /*additional_context*/ Default::default(),
             /*expected_turn_id*/ None,
+            /*client_user_message_id*/ None,
             /*responsesapi_client_metadata*/ None,
         )
         .await
@@ -8365,10 +8403,13 @@ async fn steer_input_requires_active_turn() {
 #[tokio::test]
 async fn steer_input_enforces_expected_turn_id() {
     let (sess, tc, _rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "hello".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "hello".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(
         Arc::clone(&tc),
         input,
@@ -8388,6 +8429,7 @@ async fn steer_input_enforces_expected_turn_id() {
             steer_input,
             /*additional_context*/ Default::default(),
             Some("different-turn-id"),
+            /*client_user_message_id*/ None,
             /*responsesapi_client_metadata*/ None,
         )
         .await
@@ -8411,10 +8453,13 @@ async fn steer_input_rejects_non_regular_turns() {
         (TaskKind::Compact, NonSteerableTurnKind::Compact),
     ] {
         let (sess, _tc, _rx) = make_session_and_context_with_rx().await;
-        let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-            text: "hello".to_string(),
-            text_elements: Vec::new(),
-        }])];
+        let input = vec![TurnInput::UserInput {
+            content: vec![UserInput::Text {
+                text: "hello".to_string(),
+                text_elements: Vec::new(),
+            }],
+            client_id: None,
+        }];
         let turn_context = sess.new_default_turn_with_sub_id("turn".to_string()).await;
         sess.spawn_task(
             turn_context,
@@ -8435,6 +8480,7 @@ async fn steer_input_rejects_non_regular_turns() {
                 steer_input,
                 /*additional_context*/ Default::default(),
                 /*expected_turn_id*/ None,
+                /*client_user_message_id*/ None,
                 /*responsesapi_client_metadata*/ None,
             )
             .await
@@ -8449,10 +8495,13 @@ async fn steer_input_rejects_non_regular_turns() {
 #[tokio::test]
 async fn steer_input_returns_active_turn_id() {
     let (sess, tc, _rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "hello".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "hello".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(
         Arc::clone(&tc),
         input,
@@ -8472,6 +8521,7 @@ async fn steer_input_returns_active_turn_id() {
             steer_input,
             /*additional_context*/ Default::default(),
             Some(&tc.sub_id),
+            /*client_user_message_id*/ None,
             /*responsesapi_client_metadata*/ None,
         )
         .await
@@ -9463,6 +9513,7 @@ async fn steered_input_reopens_mailbox_delivery_for_current_turn() {
         }],
         /*additional_context*/ Default::default(),
         Some(&tc.sub_id),
+        /*client_user_message_id*/ None,
         /*responsesapi_client_metadata*/ None,
     )
     .await
@@ -9471,10 +9522,13 @@ async fn steered_input_reopens_mailbox_delivery_for_current_turn() {
     assert_eq!(
         sess.input_queue.get_pending_input(&sess.active_turn).await,
         vec![
-            TurnInput::UserInput(vec![UserInput::Text {
-                text: "follow up".to_string(),
-                text_elements: Vec::new(),
-            }]),
+            TurnInput::UserInput {
+                content: vec![UserInput::Text {
+                    text: "follow up".to_string(),
+                    text_elements: Vec::new(),
+                }],
+                client_id: None
+            },
             TurnInput::ResponseItem(ResponseItem::from(communication.to_response_input_item())),
         ],
     );
@@ -9513,6 +9567,7 @@ async fn stale_defer_mailbox_delivery_does_not_override_steered_input() {
         }],
         /*additional_context*/ Default::default(),
         Some(&tc.sub_id),
+        /*client_user_message_id*/ None,
         /*responsesapi_client_metadata*/ None,
     )
     .await
@@ -9525,10 +9580,13 @@ async fn stale_defer_mailbox_delivery_does_not_override_steered_input() {
     assert_eq!(
         sess.input_queue.get_pending_input(&sess.active_turn).await,
         vec![
-            TurnInput::UserInput(vec![UserInput::Text {
-                text: "follow up".to_string(),
-                text_elements: Vec::new(),
-            }]),
+            TurnInput::UserInput {
+                content: vec![UserInput::Text {
+                    text: "follow up".to_string(),
+                    text_elements: Vec::new(),
+                }],
+                client_id: None
+            },
             TurnInput::ResponseItem(ResponseItem::from(communication.to_response_input_item())),
         ],
     );
@@ -9593,10 +9651,13 @@ async fn tool_calls_reopen_mailbox_delivery_for_current_turn() {
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn abort_review_task_emits_exited_then_aborted_and_records_history() {
     let (sess, tc, rx) = make_session_and_context_with_rx().await;
-    let input = vec![TurnInput::UserInput(vec![UserInput::Text {
-        text: "start review".to_string(),
-        text_elements: Vec::new(),
-    }])];
+    let input = vec![TurnInput::UserInput {
+        content: vec![UserInput::Text {
+            text: "start review".to_string(),
+            text_elements: Vec::new(),
+        }],
+        client_id: None,
+    }];
     sess.spawn_task(Arc::clone(&tc), input, ReviewTask::new())
         .await;
 

codex-rs/core/src/session/turn.rs

@@ -429,7 +429,7 @@ async fn run_hooks_and_record_inputs(
             blocked_input = true;
             record_additional_contexts(sess, turn_context, hook_outcome.additional_contexts).await;
         } else {
-            if matches!(input_item, TurnInput::UserInput(items) if !items.is_empty()) {
+            if matches!(input_item, TurnInput::UserInput { content, .. } if !content.is_empty()) {
                 accepted_user_input = true;
             }
             record_pending_input(
@@ -457,7 +457,7 @@ async fn build_skills_and_plugins(
     let user_input = input
         .iter()
         .filter_map(|item| match item {
-            TurnInput::UserInput(content) => Some(content.as_slice()),
+            TurnInput::UserInput { content, .. } => Some(content.as_slice()),
             TurnInput::ResponseItem(_) => None,
         })
         .flatten()
@@ -610,7 +610,7 @@ async fn track_turn_resolved_config_analytics(
             num_input_images: input
                 .iter()
                 .filter_map(|item| match item {
-                    TurnInput::UserInput(content) => Some(content.as_slice()),
+                    TurnInput::UserInput { content, .. } => Some(content.as_slice()),
                     TurnInput::ResponseItem(_) => None,
                 })
                 .flatten()

codex-rs/core/src/tasks/review.rs

@@ -72,7 +72,7 @@ impl SessionTask for ReviewTask {
         let mut user_input = Vec::new();
         for item in input {
             match item {
-                TurnInput::UserInput(mut content) => user_input.append(&mut content),
+                TurnInput::UserInput { mut content, .. } => user_input.append(&mut content),
                 TurnInput::ResponseItem(_) => {}
             }
         }

codex-rs/core/src/thread_manager_tests.rs

@@ -1124,6 +1124,7 @@ fn multi_agent_v2_interrupted_marker_uses_developer_input_message() {
 fn completed_legacy_event_history_is_not_mid_turn() {
     let completed_history = InitialHistory::Forked(vec![
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "hello".to_string(),
             images: None,
             text_elements: Vec::new(),
@@ -1152,6 +1153,7 @@ fn mixed_response_and_legacy_user_event_history_is_mid_turn() {
     let mixed_history = InitialHistory::Forked(vec![
         RolloutItem::ResponseItem(user_msg("hello")),
         RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "hello".to_string(),
             images: None,
             text_elements: Vec::new(),

codex-rs/core/tests/suite/pending_input.rs

@@ -152,6 +152,7 @@ async fn steer_user_input(codex: &CodexThread, text: &str) {
             }],
             /*additional_context*/ Default::default(),
             /*expected_turn_id*/ None,
+            /*client_user_message_id*/ None,
             /*responsesapi_client_metadata*/ None,
         )
         .await

codex-rs/core/tests/suite/personality_migration.rs

@@ -84,6 +84,7 @@ async fn write_rollout_with_user_event(dir: &Path, thread_id: ThreadId) -> io::R
     let user_event = RolloutLine {
         timestamp: TEST_TIMESTAMP.to_string(),
         item: RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "hello".to_string(),
             images: None,
             local_images: Vec::new(),

codex-rs/core/tests/suite/resume_warning.rs

@@ -56,6 +56,7 @@ fn resume_history(
                 collaboration_mode_kind: ModeKind::Default,
             })),
             RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                client_id: None,
                 message: "seed".to_string(),
                 images: None,
                 local_images: vec![],

codex-rs/core/tests/suite/sqlite_state.rs

@@ -236,6 +236,7 @@ async fn backfill_scans_existing_rollouts() -> Result<()> {
                 RolloutLine {
                     timestamp: "2026-01-27T12:00:01Z".to_string(),
                     item: RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+                        client_id: None,
                         message: "hello from backfill".to_string(),
                         images: None,
                         local_images: Vec::new(),

codex-rs/debug-client/src/client.rs

@@ -198,6 +198,7 @@ impl AppServerClient {
             request_id: request_id.clone(),
             params: TurnStartParams {
                 thread_id: thread_id.to_string(),
+                client_user_message_id: None,
                 input: vec![UserInput::Text {
                     text,
                     // Debug client sends plain text with no UI markup spans.

codex-rs/exec/src/lib.rs

@@ -779,6 +779,7 @@ async fn run_exec_session(args: ExecRunArgs) -> anyhow::Result<()> {
                     request_id: request_ids.next(),
                     params: TurnStartParams {
                         thread_id: primary_thread_id_for_span.clone(),
+                        client_user_message_id: None,
                         input: items.into_iter().map(Into::into).collect(),
                         responsesapi_client_metadata: None,
                         additional_context: None,

codex-rs/external-agent-sessions/src/export.rs

@@ -78,6 +78,7 @@ fn rollout_items_from_messages(messages: &[ConversationMessage]) -> Vec<RolloutI
                 items.push(RolloutItem::ResponseItem(response_item));
                 items.push(RolloutItem::EventMsg(EventMsg::UserMessage(
                     UserMessageEvent {
+                        client_id: None,
                         message: message.text.clone(),
                         images: None,
                         local_images: Vec::new(),

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -114,6 +114,7 @@ pub async fn run_codex_tool_session(
             additional_context: Default::default(),
             thread_settings: Default::default(),
         },
+        client_user_message_id: None,
         trace: None,
     };
 

codex-rs/mcp-server/src/message_processor.rs

@@ -539,6 +539,7 @@ impl MessageProcessor {
             .submit_with_id(Submission {
                 id: request_id_string,
                 op: codex_protocol::protocol::Op::Interrupt,
+                client_user_message_id: None,
                 trace: None,
             })
             .await

codex-rs/protocol/src/items.rs

@@ -56,6 +56,9 @@ pub enum TurnItem {
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
 pub struct UserMessageItem {
     pub id: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub client_id: Option<String>,
     pub content: Vec<UserInput>,
 }
 
@@ -237,6 +240,7 @@ impl UserMessageItem {
     pub fn new(content: &[UserInput]) -> Self {
         Self {
             id: uuid::Uuid::new_v4().to_string(),
+            client_id: None,
             content: content.to_vec(),
         }
     }
@@ -245,6 +249,7 @@ impl UserMessageItem {
         // Legacy user-message events flatten only text inputs into `message` and
         // rebase text element ranges onto that concatenated text.
         EventMsg::UserMessage(UserMessageEvent {
+            client_id: self.client_id.clone(),
             message: self.message(),
             images: Some(self.image_urls()),
             image_details: self.image_details(),
@@ -272,6 +277,7 @@ impl UserMessageItem {
             if let UserInput::Text {
                 text,
                 text_elements,
+                ..
             } = input
             {
                 // Text element ranges are relative to each text chunk; offset them so they align

codex-rs/protocol/src/models.rs

@@ -1237,7 +1237,9 @@ impl From<Vec<UserInput>> for ResponseInputItem {
                 .into_iter()
                 .flat_map(|c| match c {
                     UserInput::Text { text, .. } => vec![ContentItem::InputText { text }],
-                    UserInput::Image { image_url, detail } => {
+                    UserInput::Image {
+                        image_url, detail, ..
+                    } => {
                         image_index += 1;
                         let detail = detail.unwrap_or(DEFAULT_IMAGE_DETAIL);
                         vec![ContentItem::InputImage {
@@ -1245,7 +1247,7 @@ impl From<Vec<UserInput>> for ResponseInputItem {
                             detail: Some(detail),
                         }]
                     }
-                    UserInput::LocalImage { path, detail } => {
+                    UserInput::LocalImage { path, detail, .. } => {
                         image_index += 1;
                         let detail = detail.unwrap_or(DEFAULT_IMAGE_DETAIL);
                         match std::fs::read(&path) {

codex-rs/protocol/src/protocol.rs

@@ -129,6 +129,9 @@ pub struct Submission {
     pub id: String,
     /// Payload
     pub op: Op,
+    /// Client-provided id for the user message represented by `Op::UserInput`.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub client_user_message_id: Option<String>,
     /// Optional W3C trace carrier propagated across async submission handoffs.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub trace: Option<W3cTraceContext>,
@@ -2164,6 +2167,8 @@ pub struct AgentMessageEvent {
 
 #[derive(Debug, Clone, Default, Deserialize, Serialize, JsonSchema, TS)]
 pub struct UserMessageEvent {
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub client_id: Option<String>,
     pub message: String,
     /// Image URLs sourced from `UserInput::Image`. These are safe
     /// to replay in legacy UI history events and correspond to images sent to
@@ -5088,6 +5093,7 @@ mod tests {
     #[test]
     fn user_message_event_serializes_empty_metadata_vectors() -> Result<()> {
         let event = UserMessageEvent {
+            client_id: None,
             message: "hello".to_string(),
             images: None,
             local_images: Vec::new(),
@@ -5133,7 +5139,7 @@ mod tests {
     #[test]
     fn user_message_item_legacy_event_preserves_image_details() {
         let local_path = PathBuf::from("/tmp/local.png");
-        let item = UserMessageItem::new(&[
+        let mut item = UserMessageItem::new(&[
             crate::user_input::UserInput::Image {
                 image_url: "https://example.com/first.png".to_string(),
                 detail: Some(ImageDetail::Original),
@@ -5147,6 +5153,7 @@ mod tests {
                 detail: Some(ImageDetail::Original),
             },
         ]);
+        item.client_id = Some("client-message-1".to_string());
 
         let EventMsg::UserMessage(event) = item.as_legacy_event() else {
             panic!("expected user message event");
@@ -5159,6 +5166,7 @@ mod tests {
                 "https://example.com/second.png".to_string(),
             ])
         );
+        assert_eq!(event.client_id, Some("client-message-1".to_string()));
         assert_eq!(event.image_details, vec![Some(ImageDetail::Original)]);
         assert_eq!(event.local_images, vec![local_path]);
         assert_eq!(event.local_image_details, vec![Some(ImageDetail::Original)]);