diff --git a/codex-rs/app-server-protocol/schema/json/ClientRequest.json b/codex-rs/app-server-protocol/schema/json/ClientRequest.json
index ae8e6fed34..2da898f5c7 100644
--- a/codex-rs/app-server-protocol/schema/json/ClientRequest.json
+++ b/codex-rs/app-server-protocol/schema/json/ClientRequest.json
@@ -3116,6 +3116,16 @@
           },
           "type": "array"
         },
+        "metadata": {
+          "additionalProperties": {
+            "type": "string"
+          },
+          "description": "Optional string metadata attached only to this turn.",
+          "type": [
+            "object",
+            "null"
+          ]
+        },
         "model": {
           "description": "Override the model for this turn and subsequent turns.",
           "type": [
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
index e20953a231..40e35afc47 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
@@ -13912,6 +13912,16 @@
             },
             "type": "array"
           },
+          "metadata": {
+            "additionalProperties": {
+              "type": "string"
+            },
+            "description": "Optional string metadata attached only to this turn.",
+            "type": [
+              "object",
+              "null"
+            ]
+          },
           "model": {
             "description": "Override the model for this turn and subsequent turns.",
             "type": [
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
index cb7b2c3a0a..dc5f10f01d 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
@@ -11672,6 +11672,16 @@
           },
           "type": "array"
         },
+        "metadata": {
+          "additionalProperties": {
+            "type": "string"
+          },
+          "description": "Optional string metadata attached only to this turn.",
+          "type": [
+            "object",
+            "null"
+          ]
+        },
         "model": {
           "description": "Override the model for this turn and subsequent turns.",
           "type": [
diff --git a/codex-rs/app-server-protocol/schema/json/v2/TurnStartParams.json b/codex-rs/app-server-protocol/schema/json/v2/TurnStartParams.json
index cad1d8b5bc..8fc67ea731 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/TurnStartParams.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/TurnStartParams.json
@@ -545,6 +545,16 @@
       },
       "type": "array"
     },
+    "metadata": {
+      "additionalProperties": {
+        "type": "string"
+      },
+      "description": "Optional string metadata attached only to this turn.",
+      "type": [
+        "object",
+        "null"
+      ]
+    },
     "model": {
       "description": "Override the model for this turn and subsequent turns.",
       "type": [
diff --git a/codex-rs/app-server-protocol/schema/typescript/v2/TurnStartParams.ts b/codex-rs/app-server-protocol/schema/typescript/v2/TurnStartParams.ts
index 8f57a5e68b..76b8c054a9 100644
--- a/codex-rs/app-server-protocol/schema/typescript/v2/TurnStartParams.ts
+++ b/codex-rs/app-server-protocol/schema/typescript/v2/TurnStartParams.ts
@@ -13,6 +13,9 @@ import type { SandboxPolicy } from "./SandboxPolicy";
 import type { UserInput } from "./UserInput";
 
 export type TurnStartParams = {threadId: string, input: Array<UserInput>, /**
+ * Optional string metadata attached only to this turn.
+ */
+metadata?: { [key in string]?: string } | null, /**
  * Override the working directory for this turn and subsequent turns.
  */
 cwd?: string | null, /**
diff --git a/codex-rs/app-server-protocol/src/protocol/v2.rs b/codex-rs/app-server-protocol/src/protocol/v2.rs
index b534510b7c..41bf18798e 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2.rs
@@ -3831,6 +3831,9 @@ pub enum TurnStatus {
 pub struct TurnStartParams {
     pub thread_id: String,
     pub input: Vec<UserInput>,
+    /// Optional string metadata attached only to this turn.
+    #[ts(optional = nullable)]
+    pub metadata: Option<BTreeMap<String, String>>,
     /// Override the working directory for this turn and subsequent turns.
     #[ts(optional = nullable)]
     pub cwd: Option<PathBuf>,
@@ -7906,6 +7909,7 @@ mod tests {
         let without_override = TurnStartParams {
             thread_id: "thread_123".to_string(),
             input: vec![],
+            metadata: None,
             cwd: None,
             approval_policy: None,
             approvals_reviewer: None,
diff --git a/codex-rs/app-server/README.md b/codex-rs/app-server/README.md
index 57798a99b0..8a9a48e0fd 100644
--- a/codex-rs/app-server/README.md
+++ b/codex-rs/app-server/README.md
@@ -69,7 +69,7 @@ Use the thread APIs to create, list, or archive conversations. Drive a conversat
 - Initialize once per connection: Immediately after opening a transport connection, send an `initialize` request with your client metadata, then emit an `initialized` notification. Any other request on that connection before this handshake gets rejected.
 - Start (or resume) a thread: Call `thread/start` to open a fresh conversation. The response returns the thread object and you’ll also get a `thread/started` notification. If you’re continuing an existing conversation, call `thread/resume` with its ID instead. If you want to branch from an existing conversation, call `thread/fork` to create a new thread id with copied history. Like `thread/start`, `thread/fork` also accepts `ephemeral: true` for an in-memory temporary thread.
   The returned `thread.ephemeral` flag tells you whether the session is intentionally in-memory only; when it is `true`, `thread.path` is `null`.
-- Begin a turn: To send user input, call `turn/start` with the target `threadId` and the user's input. Optional fields let you override model, cwd, sandbox policy, approval policy, approvals reviewer, etc. This immediately returns the new turn object. The app-server emits `turn/started` when that turn actually begins running.
+- Begin a turn: To send user input, call `turn/start` with the target `threadId` and the user's input. Optional fields let you override model, cwd, sandbox policy, approval policy, approvals reviewer, etc. `turn/start.metadata` also lets callers attach arbitrary string metadata to that turn. This immediately returns the new turn object. The app-server emits `turn/started` when that turn actually begins running.
 - Stream events: After `turn/start`, keep reading JSON-RPC notifications on stdout. You’ll see `item/started`, `item/completed`, deltas like `item/agentMessage/delta`, tool progress, etc. These represent streaming model output plus any side effects (commands, tool calls, reasoning notes).
 - Finish the turn: When the model is done (or the turn is interrupted via making the `turn/interrupt` call), the server sends `turn/completed` with the final turn state and token usage.
 
@@ -139,7 +139,7 @@ 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. 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. `metadata` accepts arbitrary string key/value pairs for turn-scoped observability and request forwarding. For `collaborationMode`, `settings.developer_instructions: null` means "use built-in instructions for the selected mode".
 - `turn/steer` — add user input to an already in-flight turn without starting a new turn; returns the active `turnId` that accepted the input.
 - `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); returns `{}` and streams `thread/realtime/*` notifications.
diff --git a/codex-rs/app-server/src/codex_message_processor.rs b/codex-rs/app-server/src/codex_message_processor.rs
index b6ece83ddf..0a54b9346a 100644
--- a/codex-rs/app-server/src/codex_message_processor.rs
+++ b/codex-rs/app-server/src/codex_message_processor.rs
@@ -6018,6 +6018,7 @@ impl CodexMessageProcessor {
                 Op::UserInput {
                     items: mapped_items,
                     final_output_json_schema: params.output_schema,
+                    metadata: params.metadata,
                 },
             )
             .await;
diff --git a/codex-rs/app-server/src/in_process.rs b/codex-rs/app-server/src/in_process.rs
index 4288d15393..5ff3e4e95c 100644
--- a/codex-rs/app-server/src/in_process.rs
+++ b/codex-rs/app-server/src/in_process.rs
@@ -857,6 +857,176 @@ mod tests {
             .expect("in-process runtime should shutdown cleanly");
     }
 
+    #[tokio::test]
+    async fn in_process_start_forwards_turn_metadata_headers_on_turn_requests() {
+        let server = create_mock_responses_server_repeating_assistant("Done").await;
+        let codex_home = TempDir::new().expect("tempdir should create");
+        let mut client = start(InProcessStartArgs {
+            arg0_paths: Arg0DispatchPaths::default(),
+            config: Arc::new(
+                ConfigBuilder::default()
+                    .codex_home(codex_home.path().to_path_buf())
+                    .build()
+                    .await
+                    .expect("test config should load"),
+            ),
+            cli_overrides: vec![
+                (
+                    "model_provider".to_string(),
+                    TomlValue::String("mock_provider".to_string()),
+                ),
+                (
+                    "model_providers.mock_provider.name".to_string(),
+                    TomlValue::String("Mock provider for test".to_string()),
+                ),
+                (
+                    "model_providers.mock_provider.base_url".to_string(),
+                    TomlValue::String(format!("{}/v1", server.uri())),
+                ),
+                (
+                    "model_providers.mock_provider.wire_api".to_string(),
+                    TomlValue::String("responses".to_string()),
+                ),
+                (
+                    "model_providers.mock_provider.request_max_retries".to_string(),
+                    TomlValue::Integer(0),
+                ),
+                (
+                    "model_providers.mock_provider.stream_max_retries".to_string(),
+                    TomlValue::Integer(0),
+                ),
+            ],
+            loader_overrides: LoaderOverrides::default(),
+            cloud_requirements: CloudRequirementsLoader::default(),
+            auth_manager: None,
+            thread_manager: None,
+            feedback: CodexFeedback::new(),
+            config_warnings: Vec::new(),
+            session_source: SessionSource::Cli,
+            enable_codex_api_key_env: false,
+            initialize: InitializeParams {
+                client_info: ClientInfo {
+                    name: "codex-in-process-test".to_string(),
+                    title: None,
+                    version: "0.0.0".to_string(),
+                },
+                capabilities: None,
+            },
+            channel_capacity: DEFAULT_IN_PROCESS_CHANNEL_CAPACITY,
+        })
+        .await
+        .expect("in-process runtime should start");
+
+        let thread_start_response: ThreadStartResponse = serde_json::from_value(
+            client
+                .request(ClientRequest::ThreadStart {
+                    request_id: RequestId::Integer(5),
+                    params: ThreadStartParams {
+                        model: Some("mock-model".to_string()),
+                        ephemeral: Some(true),
+                        ..ThreadStartParams::default()
+                    },
+                })
+                .await
+                .expect("thread/start request should work")
+                .expect("thread/start should succeed"),
+        )
+        .expect("thread/start response should parse");
+
+        let _turn_start_response: TurnStartResponse = serde_json::from_value(
+            client
+                .request(ClientRequest::TurnStart {
+                    request_id: RequestId::Integer(6),
+                    params: TurnStartParams {
+                        thread_id: thread_start_response.thread.id,
+                        input: vec![UserInput::Text {
+                            text: "Hello".to_string(),
+                            text_elements: Vec::new(),
+                        }],
+                        metadata: Some(std::collections::BTreeMap::from([
+                            (
+                                "parentConversationId".to_string(),
+                                "parent-conversation-123".to_string(),
+                            ),
+                            (
+                                "parentMessageId".to_string(),
+                                "parent-message-123".to_string(),
+                            ),
+                            ("parentTurnId".to_string(), "parent-turn-123".to_string()),
+                        ])),
+                        ..TurnStartParams::default()
+                    },
+                })
+                .await
+                .expect("turn/start request should work")
+                .expect("turn/start should succeed"),
+        )
+        .expect("turn/start response should parse");
+
+        let turn_completed = loop {
+            let event = timeout(std::time::Duration::from_secs(10), client.next_event())
+                .await
+                .expect("timed out waiting for turn completion");
+            match event {
+                Some(InProcessServerEvent::ServerNotification(
+                    ServerNotification::TurnCompleted(notification),
+                )) => break notification,
+                Some(_) => continue,
+                None => panic!("in-process runtime exited before turn completion"),
+            }
+        };
+        assert_eq!(
+            turn_completed.turn.status,
+            TurnStatus::Completed,
+            "turn error: {:?}",
+            turn_completed.turn.error
+        );
+        assert_eq!(turn_completed.turn.error, None);
+
+        let requests = timeout(std::time::Duration::from_secs(5), async {
+            loop {
+                let requests = server
+                    .received_requests()
+                    .await
+                    .expect("received requests should be available");
+                if !requests.is_empty() {
+                    break requests;
+                }
+                tokio::task::yield_now().await;
+            }
+        })
+        .await
+        .expect("timed out waiting for outbound requests");
+        assert!(!requests.is_empty());
+        for request in requests {
+            assert_eq!(
+                request
+                    .headers
+                    .get("x-openai-parent-conversation-id")
+                    .and_then(|value| value.to_str().ok()),
+                Some("parent-conversation-123")
+            );
+            assert_eq!(
+                request
+                    .headers
+                    .get("x-openai-parent-message-id")
+                    .and_then(|value| value.to_str().ok()),
+                Some("parent-message-123")
+            );
+            assert_eq!(
+                request
+                    .headers
+                    .get("x-openai-parent-turn-id")
+                    .and_then(|value| value.to_str().ok()),
+                Some("parent-turn-123")
+            );
+        }
+
+        client
+            .shutdown()
+            .await
+            .expect("in-process runtime should shutdown cleanly");
+    }
     #[test]
     fn guaranteed_delivery_helpers_cover_terminal_notifications() {
         assert!(server_notification_requires_delivery(
diff --git a/codex-rs/app-server/src/message_processor/tracing_tests.rs b/codex-rs/app-server/src/message_processor/tracing_tests.rs
index e39484cedb..7d86c86e90 100644
--- a/codex-rs/app-server/src/message_processor/tracing_tests.rs
+++ b/codex-rs/app-server/src/message_processor/tracing_tests.rs
@@ -601,6 +601,7 @@ async fn turn_start_jsonrpc_span_parents_core_turn_spans() -> Result<()> {
                     personality: None,
                     output_schema: None,
                     collaboration_mode: None,
+                    metadata: None,
                 },
             },
             Some(remote_trace),
diff --git a/codex-rs/app-server/tests/suite/v2/turn_start.rs b/codex-rs/app-server/tests/suite/v2/turn_start.rs
index e235ee6b61..2a6faf5788 100644
--- a/codex-rs/app-server/tests/suite/v2/turn_start.rs
+++ b/codex-rs/app-server/tests/suite/v2/turn_start.rs
@@ -1395,6 +1395,7 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
             personality: None,
             output_schema: None,
             collaboration_mode: None,
+            metadata: None,
         })
         .await?;
     timeout(
@@ -1428,6 +1429,7 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
             personality: None,
             output_schema: None,
             collaboration_mode: None,
+            metadata: None,
         })
         .await?;
     timeout(
diff --git a/codex-rs/core/src/agent/control.rs b/codex-rs/core/src/agent/control.rs
index 83af6258fb..1b76cce5fd 100644
--- a/codex-rs/core/src/agent/control.rs
+++ b/codex-rs/core/src/agent/control.rs
@@ -424,6 +424,7 @@ impl AgentControl {
                 Op::UserInput {
                     items,
                     final_output_json_schema: None,
+                    metadata: None,
                 },
             )
             .await;
diff --git a/codex-rs/core/src/agent/control_tests.rs b/codex-rs/core/src/agent/control_tests.rs
index 7c2c46b2f3..50660a739e 100644
--- a/codex-rs/core/src/agent/control_tests.rs
+++ b/codex-rs/core/src/agent/control_tests.rs
@@ -372,6 +372,7 @@ async fn send_input_submits_user_message() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+            metadata: None,
         },
     );
     let captured = harness
@@ -403,6 +404,7 @@ async fn spawn_agent_creates_thread_and_sends_prompt() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+            metadata: None,
         },
     );
     let captured = harness
@@ -479,6 +481,7 @@ async fn spawn_agent_can_fork_parent_thread_history() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+            metadata: None,
         },
     );
     let captured = harness
diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index ba71033c3b..70c4bfa44c 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -108,6 +108,7 @@ use crate::response_debug_context::extract_response_debug_context_from_api_error
 use crate::response_debug_context::telemetry_api_error_message;
 use crate::response_debug_context::telemetry_transport_error_message;
 use crate::tools::spec::create_tools_json_for_responses_api;
+use crate::turn_metadata::extend_known_request_headers;
 use crate::util::FeedbackRequestTags;
 use crate::util::emit_feedback_auth_recovery_tags;
 use crate::util::emit_feedback_request_tags_with_auth_env;
@@ -469,6 +470,9 @@ impl ModelClient {
         extra_headers
     }
 
+    fn build_session_request_headers(&self) -> ApiHeaderMap {
+        self.build_subagent_headers()
+    }
     /// Builds request telemetry for unary API calls (e.g., Compact endpoint).
     fn build_request_telemetry(
         session_telemetry: &SessionTelemetry,
@@ -1384,6 +1388,10 @@ fn build_responses_headers(
     turn_metadata_header: Option<&HeaderValue>,
 ) -> ApiHeaderMap {
     let mut headers = ApiHeaderMap::new();
+    extend_known_request_headers(
+        &mut headers,
+        turn_metadata_header.and_then(|value| value.to_str().ok()),
+    );
     if let Some(value) = beta_features_header
         && !value.is_empty()
         && let Ok(header_value) = HeaderValue::from_str(value)
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 931300cf4e..3e9832977d 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -1,3 +1,4 @@
+use std::collections::BTreeMap;
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::fmt::Debug;
@@ -590,6 +591,7 @@ impl Codex {
             persist_extended_history,
             inherited_shell_snapshot,
             user_shell_override,
+            next_turn_metadata: BTreeMap::new(),
         };
 
         // Generate a unique ID for the lifetime of this Codex session.
@@ -1055,6 +1057,8 @@ pub(crate) struct SessionConfiguration {
     persist_extended_history: bool,
     inherited_shell_snapshot: Option<Arc<ShellSnapshot>>,
     user_shell_override: Option<shell::Shell>,
+    /// One-shot metadata consumed by the next turn created from this session.
+    next_turn_metadata: BTreeMap<String, String>,
 }
 
 impl SessionConfiguration {
@@ -1097,6 +1101,9 @@ impl SessionConfiguration {
         if let Some(personality) = updates.personality {
             next_configuration.personality = Some(personality);
         }
+        if let Some(next_turn_metadata) = updates.next_turn_metadata.clone() {
+            next_configuration.next_turn_metadata = next_turn_metadata;
+        }
         if let Some(approval_policy) = updates.approval_policy {
             next_configuration.approval_policy.set(approval_policy)?;
         }
@@ -1147,6 +1154,8 @@ pub(crate) struct SessionSettingsUpdate {
     pub(crate) final_output_json_schema: Option<Option<Value>>,
     pub(crate) personality: Option<Personality>,
     pub(crate) app_server_client_name: Option<String>,
+    /// One-shot metadata for the next turn created from this update.
+    pub(crate) next_turn_metadata: Option<BTreeMap<String, String>>,
 }
 
 impl Session {
@@ -1341,6 +1350,7 @@ impl Session {
             cwd.clone(),
             session_configuration.sandbox_policy.get(),
             session_configuration.windows_sandbox_level,
+            session_configuration.next_turn_metadata.clone(),
         ));
         let (current_date, timezone) = local_time_context();
         TurnContext {
@@ -2036,6 +2046,7 @@ impl Session {
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+                metadata: None,
             },
         )
         .await;
@@ -2305,7 +2316,9 @@ impl Session {
                         state.session_configuration.sandbox_policy != next.sandbox_policy;
                     let codex_home = next.codex_home.clone();
                     let session_source = next.session_source.clone();
-                    state.session_configuration = next.clone();
+                    let mut persisted_configuration = next.clone();
+                    persisted_configuration.next_turn_metadata.clear();
+                    state.session_configuration = persisted_configuration;
                     (
                         next,
                         sandbox_policy_changed,
@@ -4491,6 +4504,7 @@ mod handlers {
                         reasoning_summary: summary,
                         service_tier,
                         final_output_json_schema: Some(final_output_json_schema),
+                        next_turn_metadata: None,
                         personality,
                         app_server_client_name: None,
                     },
@@ -4499,10 +4513,12 @@ mod handlers {
             Op::UserInput {
                 items,
                 final_output_json_schema,
+                metadata,
             } => (
                 items,
                 SessionSettingsUpdate {
                     final_output_json_schema: Some(final_output_json_schema),
+                    next_turn_metadata: Some(metadata.unwrap_or_default()),
                     ..Default::default()
                 },
             ),
@@ -5225,6 +5241,7 @@ async fn spawn_review_thread(
         parent_turn_context.cwd.clone(),
         parent_turn_context.sandbox_policy.get(),
         parent_turn_context.windows_sandbox_level,
+        parent_turn_context.turn_metadata_state.metadata().clone(),
     ));
 
     let review_turn_context = TurnContext {
diff --git a/codex-rs/core/src/codex_delegate.rs b/codex-rs/core/src/codex_delegate.rs
index e560cd9c7f..54261d6bcd 100644
--- a/codex-rs/core/src/codex_delegate.rs
+++ b/codex-rs/core/src/codex_delegate.rs
@@ -170,6 +170,7 @@ pub(crate) async fn run_codex_thread_one_shot(
     io.submit(Op::UserInput {
         items: input,
         final_output_json_schema,
+        metadata: None,
     })
     .await?;
 
diff --git a/codex-rs/core/src/codex_tests.rs b/codex-rs/core/src/codex_tests.rs
index c7cbcf2252..440b240366 100644
--- a/codex-rs/core/src/codex_tests.rs
+++ b/codex-rs/core/src/codex_tests.rs
@@ -1660,6 +1660,7 @@ async fn set_rate_limits_retains_previous_credits() {
         persist_extended_history: false,
         inherited_shell_snapshot: None,
         user_shell_override: None,
+        next_turn_metadata: std::collections::BTreeMap::new(),
     };
 
     let mut state = SessionState::new(session_configuration);
@@ -1758,6 +1759,7 @@ async fn set_rate_limits_updates_plan_type_when_present() {
         persist_extended_history: false,
         inherited_shell_snapshot: None,
         user_shell_override: None,
+        next_turn_metadata: std::collections::BTreeMap::new(),
     };
 
     let mut state = SessionState::new(session_configuration);
@@ -2102,6 +2104,7 @@ pub(crate) async fn make_session_configuration_for_tests() -> SessionConfigurati
         persist_extended_history: false,
         inherited_shell_snapshot: None,
         user_shell_override: None,
+        next_turn_metadata: std::collections::BTreeMap::new(),
     }
 }
 
@@ -2333,6 +2336,7 @@ async fn session_new_fails_when_zsh_fork_enabled_without_zsh_path() {
         persist_extended_history: false,
         inherited_shell_snapshot: None,
         user_shell_override: None,
+        next_turn_metadata: std::collections::BTreeMap::new(),
     };
 
     let (tx_event, _rx_event) = async_channel::unbounded();
@@ -2428,6 +2432,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         persist_extended_history: false,
         inherited_shell_snapshot: None,
         user_shell_override: None,
+        next_turn_metadata: std::collections::BTreeMap::new(),
     };
     let per_turn_config = Session::build_per_turn_config(&session_configuration);
     let model_info = ModelsManager::construct_model_info_offline_for_tests(
@@ -2865,6 +2870,7 @@ fn op_kind_distinguishes_turn_ops() {
         Op::UserInput {
             items: vec![],
             final_output_json_schema: None,
+            metadata: None,
         }
         .kind(),
         "user_input"
@@ -3223,6 +3229,7 @@ pub(crate) async fn make_session_and_context_with_dynamic_tools_and_rx(
         persist_extended_history: false,
         inherited_shell_snapshot: None,
         user_shell_override: None,
+        next_turn_metadata: std::collections::BTreeMap::new(),
     };
     let per_turn_config = Session::build_per_turn_config(&session_configuration);
     let model_info = ModelsManager::construct_model_info_offline_for_tests(
diff --git a/codex-rs/core/src/mcp_tool_call.rs b/codex-rs/core/src/mcp_tool_call.rs
index 16a05df957..ac76f7c9a8 100644
--- a/codex-rs/core/src/mcp_tool_call.rs
+++ b/codex-rs/core/src/mcp_tool_call.rs
@@ -33,6 +33,7 @@ use crate::protocol::McpInvocation;
 use crate::protocol::McpToolCallBeginEvent;
 use crate::protocol::McpToolCallEndEvent;
 use crate::state_db;
+use crate::turn_metadata::extend_known_request_headers;
 use codex_protocol::mcp::CallToolResult;
 use codex_protocol::openai_models::InputModality;
 use codex_protocol::protocol::AskForApproval;
@@ -389,7 +390,6 @@ pub(crate) struct McpToolApprovalMetadata {
 }
 
 const MCP_TOOL_CODEX_APPS_META_KEY: &str = "_codex_apps";
-
 fn build_mcp_tool_call_request_meta(
     turn_context: &TurnContext,
     server: &str,
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
index be34a15707..e51f71caa3 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -557,6 +557,7 @@ async fn send_input_accepts_structured_items() {
             },
         ],
         final_output_json_schema: None,
+        metadata: None,
     };
     let captured = manager
         .captured_ops()
diff --git a/codex-rs/core/src/turn_metadata.rs b/codex-rs/core/src/turn_metadata.rs
index 3a4bac011d..fd3f1e3522 100644
--- a/codex-rs/core/src/turn_metadata.rs
+++ b/codex-rs/core/src/turn_metadata.rs
@@ -5,6 +5,9 @@ use std::sync::Arc;
 use std::sync::Mutex;
 use std::sync::RwLock;
 
+use http::HeaderMap;
+use http::HeaderValue;
+use serde::Deserialize;
 use serde::Serialize;
 use tokio::task::JoinHandle;
 
@@ -16,6 +19,14 @@ use crate::sandbox_tags::sandbox_tag;
 use codex_protocol::config_types::WindowsSandboxLevel;
 use codex_protocol::protocol::SandboxPolicy;
 
+pub(crate) const PARENT_CONVERSATION_ID_METADATA_KEY: &str = "parentConversationId";
+pub(crate) const PARENT_MESSAGE_ID_METADATA_KEY: &str = "parentMessageId";
+pub(crate) const PARENT_TURN_ID_METADATA_KEY: &str = "parentTurnId";
+
+const X_OPENAI_PARENT_CONVERSATION_ID_HEADER: &str = "x-openai-parent-conversation-id";
+const X_OPENAI_PARENT_MESSAGE_ID_HEADER: &str = "x-openai-parent-message-id";
+const X_OPENAI_PARENT_TURN_ID_HEADER: &str = "x-openai-parent-turn-id";
+
 #[derive(Clone, Debug, Default)]
 struct WorkspaceGitMetadata {
     associated_remote_urls: Option<BTreeMap<String, String>>,
@@ -31,7 +42,7 @@ impl WorkspaceGitMetadata {
     }
 }
 
-#[derive(Clone, Debug, Serialize, Default)]
+#[derive(Clone, Debug, Deserialize, Serialize, Default)]
 struct TurnMetadataWorkspace {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     associated_remote_urls: Option<BTreeMap<String, String>>,
@@ -51,7 +62,7 @@ impl From<WorkspaceGitMetadata> for TurnMetadataWorkspace {
     }
 }
 
-#[derive(Clone, Debug, Serialize, Default)]
+#[derive(Clone, Debug, Deserialize, Serialize, Default)]
 pub(crate) struct TurnMetadataBag {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     session_id: Option<String>,
@@ -61,6 +72,8 @@ pub(crate) struct TurnMetadataBag {
     workspaces: BTreeMap<String, TurnMetadataWorkspace>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     sandbox: Option<String>,
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
+    metadata: BTreeMap<String, String>,
 }
 
 impl TurnMetadataBag {
@@ -75,6 +88,7 @@ fn build_turn_metadata_bag(
     sandbox: Option<String>,
     repo_root: Option<String>,
     workspace_git_metadata: Option<WorkspaceGitMetadata>,
+    metadata: BTreeMap<String, String>,
 ) -> TurnMetadataBag {
     let mut workspaces = BTreeMap::new();
     if let (Some(repo_root), Some(workspace_git_metadata)) = (repo_root, workspace_git_metadata)
@@ -88,6 +102,7 @@ fn build_turn_metadata_bag(
         turn_id,
         workspaces,
         sandbox,
+        metadata,
     }
 }
 
@@ -117,6 +132,7 @@ pub async fn build_turn_metadata_header(cwd: &Path, sandbox: Option<&str>) -> Op
             latest_git_commit_hash,
             has_changes,
         }),
+        BTreeMap::new(),
     )
     .to_header_value()
 }
@@ -138,6 +154,7 @@ impl TurnMetadataState {
         cwd: PathBuf,
         sandbox_policy: &SandboxPolicy,
         windows_sandbox_level: WindowsSandboxLevel,
+        metadata: BTreeMap<String, String>,
     ) -> Self {
         let repo_root = get_git_repo_root(&cwd).map(|root| root.to_string_lossy().into_owned());
         let sandbox = Some(sandbox_tag(sandbox_policy, windows_sandbox_level).to_string());
@@ -147,6 +164,7 @@ impl TurnMetadataState {
             sandbox,
             /*repo_root*/ None,
             /*workspace_git_metadata*/ None,
+            metadata,
         );
         let base_header = base_metadata
             .to_header_value()
@@ -180,6 +198,10 @@ impl TurnMetadataState {
             .and_then(|header| serde_json::from_str(&header).ok())
     }
 
+    pub(crate) fn metadata(&self) -> &BTreeMap<String, String> {
+        &self.base_metadata.metadata
+    }
+
     pub(crate) fn spawn_git_enrichment_task(&self) {
         if self.repo_root.is_none() {
             return;
@@ -206,6 +228,7 @@ impl TurnMetadataState {
                 state.base_metadata.sandbox.clone(),
                 Some(repo_root),
                 Some(workspace_git_metadata),
+                state.base_metadata.metadata.clone(),
             );
             if enriched_metadata.workspaces.is_empty() {
                 return;
@@ -245,6 +268,51 @@ impl TurnMetadataState {
     }
 }
 
+pub(crate) fn extend_known_request_headers(
+    headers: &mut HeaderMap,
+    turn_metadata_header: Option<&str>,
+) {
+    let Some(turn_metadata_header) = turn_metadata_header else {
+        return;
+    };
+    let Ok(turn_metadata) = serde_json::from_str::<TurnMetadataBag>(turn_metadata_header) else {
+        return;
+    };
+
+    insert_if_valid(
+        headers,
+        X_OPENAI_PARENT_CONVERSATION_ID_HEADER,
+        turn_metadata
+            .metadata
+            .get(PARENT_CONVERSATION_ID_METADATA_KEY)
+            .map(String::as_str),
+    );
+    insert_if_valid(
+        headers,
+        X_OPENAI_PARENT_MESSAGE_ID_HEADER,
+        turn_metadata
+            .metadata
+            .get(PARENT_MESSAGE_ID_METADATA_KEY)
+            .map(String::as_str),
+    );
+    insert_if_valid(
+        headers,
+        X_OPENAI_PARENT_TURN_ID_HEADER,
+        turn_metadata
+            .metadata
+            .get(PARENT_TURN_ID_METADATA_KEY)
+            .map(String::as_str),
+    );
+}
+
+fn insert_if_valid(headers: &mut HeaderMap, name: &'static str, value: Option<&str>) {
+    if let Some(value) = value
+        && let Ok(header_value) = HeaderValue::from_str(value)
+    {
+        headers.insert(name, header_value);
+    }
+}
+
 #[cfg(test)]
 #[path = "turn_metadata_tests.rs"]
 mod tests;
diff --git a/codex-rs/core/src/turn_metadata_tests.rs b/codex-rs/core/src/turn_metadata_tests.rs
index 5da26563f6..69df990b41 100644
--- a/codex-rs/core/src/turn_metadata_tests.rs
+++ b/codex-rs/core/src/turn_metadata_tests.rs
@@ -1,5 +1,7 @@
 use super::*;
 
+use std::collections::BTreeMap;
+
 use serde_json::Value;
 use tempfile::TempDir;
 use tokio::process::Command;
@@ -72,6 +74,7 @@ fn turn_metadata_state_uses_platform_sandbox_tag() {
         cwd,
         &sandbox_policy,
         WindowsSandboxLevel::Disabled,
+        BTreeMap::new(),
     );
 
     let header = state.current_header_value().expect("header");
@@ -83,3 +86,38 @@ fn turn_metadata_state_uses_platform_sandbox_tag() {
     assert_eq!(sandbox_name, Some(expected_sandbox));
     assert_eq!(session_id, Some("session-a"));
 }
+
+#[test]
+fn extend_known_request_headers_reads_parent_ids_from_turn_metadata() {
+    let mut headers = http::HeaderMap::new();
+    let turn_metadata = serde_json::json!({
+        "turn_id": "turn-a",
+        "metadata": {
+            PARENT_CONVERSATION_ID_METADATA_KEY: "conv-123",
+            PARENT_MESSAGE_ID_METADATA_KEY: "msg-123",
+            PARENT_TURN_ID_METADATA_KEY: "turn-123",
+        },
+    });
+    let turn_metadata = serde_json::to_string(&turn_metadata).expect("turn metadata json");
+
+    extend_known_request_headers(&mut headers, Some(turn_metadata.as_str()));
+
+    assert_eq!(
+        headers
+            .get("x-openai-parent-conversation-id")
+            .and_then(|value| value.to_str().ok()),
+        Some("conv-123")
+    );
+    assert_eq!(
+        headers
+            .get("x-openai-parent-message-id")
+            .and_then(|value| value.to_str().ok()),
+        Some("msg-123")
+    );
+    assert_eq!(
+        headers
+            .get("x-openai-parent-turn-id")
+            .and_then(|value| value.to_str().ok()),
+        Some("turn-123")
+    );
+}
diff --git a/codex-rs/core/tests/responses_headers.rs b/codex-rs/core/tests/responses_headers.rs
index 823057797c..12b6173fbd 100644
--- a/codex-rs/core/tests/responses_headers.rs
+++ b/codex-rs/core/tests/responses_headers.rs
@@ -20,6 +20,7 @@ use core_test_support::responses;
 use core_test_support::test_codex::test_codex;
 use futures::StreamExt;
 use pretty_assertions::assert_eq;
+use serde_json::json;
 use tempfile::TempDir;
 use wiremock::matchers::header;
 
@@ -546,3 +547,129 @@ async fn responses_stream_includes_turn_metadata_header_for_git_workspace_e2e()
         Some(false)
     );
 }
+
+#[tokio::test]
+async fn responses_stream_includes_parent_headers_from_turn_metadata() {
+    core_test_support::skip_if_no_network!();
+
+    let server = responses::start_mock_server().await;
+    let request_recorder = responses::mount_sse_once(
+        &server,
+        responses::sse(vec![
+            responses::ev_response_created("resp-1"),
+            responses::ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+
+    let provider = ModelProviderInfo {
+        name: "mock".into(),
+        base_url: Some(format!("{}/v1", server.uri())),
+        env_key: None,
+        env_key_instructions: None,
+        experimental_bearer_token: None,
+        wire_api: WireApi::Responses,
+        query_params: None,
+        http_headers: None,
+        env_http_headers: None,
+        request_max_retries: Some(0),
+        stream_max_retries: Some(0),
+        stream_idle_timeout_ms: Some(5_000),
+        websocket_connect_timeout_ms: None,
+        requires_openai_auth: false,
+        supports_websockets: false,
+    };
+
+    let codex_home = TempDir::new().expect("failed to create TempDir");
+    let mut config = load_default_config_for_test(&codex_home).await;
+    config.model_provider_id = provider.name.clone();
+    config.model_provider = provider.clone();
+    let effort = config.model_reasoning_effort;
+    let summary = config.model_reasoning_summary;
+    let model = codex_core::test_support::get_model_offline(config.model.as_deref());
+    config.model = Some(model.clone());
+    let config = Arc::new(config);
+
+    let conversation_id = ThreadId::new();
+    let auth_mode = TelemetryAuthMode::Chatgpt;
+    let session_source = SessionSource::Exec;
+    let model_info =
+        codex_core::test_support::construct_model_info_offline(model.as_str(), &config);
+    let session_telemetry = SessionTelemetry::new(
+        conversation_id,
+        model.as_str(),
+        model_info.slug.as_str(),
+        None,
+        Some("test@test.com".to_string()),
+        Some(auth_mode),
+        "test_originator".to_string(),
+        false,
+        "test".to_string(),
+        session_source.clone(),
+    );
+
+    let client = ModelClient::new(
+        None,
+        conversation_id,
+        provider,
+        session_source,
+        config.model_verbosity,
+        false,
+        false,
+        false,
+        None,
+    );
+    let mut client_session = client.new_session();
+
+    let mut prompt = Prompt::default();
+    prompt.input = vec![ResponseItem::Message {
+        id: None,
+        role: "user".into(),
+        content: vec![ContentItem::InputText {
+            text: "hello".into(),
+        }],
+        end_turn: None,
+        phase: None,
+    }];
+    let turn_metadata_header = serde_json::to_string(&json!({
+        "turn_id": "turn-123",
+        "metadata": {
+            "parentConversationId": "conv-123",
+            "parentMessageId": "msg-123",
+            "parentTurnId": "turn-123",
+        },
+    }))
+    .expect("turn metadata json");
+
+    let mut stream = client_session
+        .stream(
+            &prompt,
+            &model_info,
+            &session_telemetry,
+            effort,
+            summary.unwrap_or(model_info.default_reasoning_summary),
+            None,
+            Some(turn_metadata_header.as_str()),
+        )
+        .await
+        .expect("stream failed");
+    while let Some(event) = stream.next().await {
+        if matches!(event, Ok(ResponseEvent::Completed { .. })) {
+            break;
+        }
+    }
+
+    let request = request_recorder.single_request();
+    assert_eq!(
+        request.header("x-openai-parent-conversation-id").as_deref(),
+        Some("conv-123")
+    );
+    assert_eq!(
+        request.header("x-openai-parent-message-id").as_deref(),
+        Some("msg-123")
+    );
+    assert_eq!(
+        request.header("x-openai-parent-turn-id").as_deref(),
+        Some("turn-123")
+    );
+}
diff --git a/codex-rs/core/tests/suite/abort_tasks.rs b/codex-rs/core/tests/suite/abort_tasks.rs
index af3c70b74e..839568e85d 100644
--- a/codex-rs/core/tests/suite/abort_tasks.rs
+++ b/codex-rs/core/tests/suite/abort_tasks.rs
@@ -51,6 +51,8 @@ async fn interrupt_long_running_tool_emits_turn_aborted() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -105,6 +107,8 @@ async fn interrupt_tool_records_history_entries() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -123,6 +127,8 @@ async fn interrupt_tool_records_history_entries() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -203,6 +209,8 @@ async fn interrupt_persists_turn_aborted_marker_in_next_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -221,6 +229,8 @@ async fn interrupt_persists_turn_aborted_marker_in_next_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index 35dee3fa70..ef24b90437 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -277,6 +277,8 @@ async fn resume_includes_initial_messages_and_sends_prior_items() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -639,6 +641,8 @@ async fn includes_conversation_id_and_model_headers_in_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -687,6 +691,8 @@ async fn includes_base_instructions_override_in_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -739,6 +745,8 @@ async fn chatgpt_auth_sends_correct_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -841,6 +849,8 @@ async fn prefers_apikey_when_config_prefers_apikey_even_with_chatgpt_tokens() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -877,6 +887,8 @@ async fn includes_user_instructions_message_in_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -962,6 +974,8 @@ async fn includes_apps_guidance_as_developer_message_for_chatgpt_auth() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1050,6 +1064,8 @@ async fn omits_apps_guidance_for_api_key_auth_even_when_feature_enabled() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1120,6 +1136,8 @@ async fn skills_append_to_developer_message() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1171,6 +1189,8 @@ async fn includes_configured_effort_in_request() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1213,6 +1233,8 @@ async fn includes_no_effort_in_request() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1253,6 +1275,8 @@ async fn includes_default_reasoning_effort_in_request_when_defined_by_model_info
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1364,6 +1388,8 @@ async fn configured_reasoning_summary_is_sent() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1478,6 +1504,8 @@ async fn reasoning_summary_is_omitted_when_disabled() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1534,6 +1562,8 @@ async fn reasoning_summary_none_overrides_model_catalog_default() -> anyhow::Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1570,6 +1600,8 @@ async fn includes_default_verbosity_in_request() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1615,6 +1647,8 @@ async fn configured_verbosity_not_sent_for_models_without_support() -> anyhow::R
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1659,6 +1693,8 @@ async fn configured_verbosity_is_sent() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1708,6 +1744,8 @@ async fn includes_developer_instructions_message_in_request() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1992,6 +2030,8 @@ async fn token_count_includes_rate_limits_snapshot() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2157,6 +2197,8 @@ async fn usage_limit_error_emits_rate_limit_event() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submission should succeed while emitting usage limit error events");
@@ -2231,6 +2273,8 @@ async fn context_window_error_sets_total_tokens_to_model_window() -> anyhow::Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -2243,6 +2287,8 @@ async fn context_window_error_sets_total_tokens_to_model_window() -> anyhow::Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -2325,6 +2371,8 @@ async fn incomplete_response_emits_content_filter_error_message() -> anyhow::Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -2423,6 +2471,8 @@ async fn azure_overrides_assign_properties_used_for_responses_url() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2508,6 +2558,8 @@ async fn env_var_overrides_loaded_auth() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2569,6 +2621,8 @@ async fn history_dedupes_streamed_and_final_messages_across_turns() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2582,6 +2636,8 @@ async fn history_dedupes_streamed_and_final_messages_across_turns() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2595,6 +2651,8 @@ async fn history_dedupes_streamed_and_final_messages_across_turns() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/client_websockets.rs b/codex-rs/core/tests/suite/client_websockets.rs
index 4416ff1083..c283332c86 100755
--- a/codex-rs/core/tests/suite/client_websockets.rs
+++ b/codex-rs/core/tests/suite/client_websockets.rs
@@ -996,6 +996,8 @@ async fn responses_websocket_usage_limit_error_emits_rate_limit_event() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submission should succeed while emitting usage limit error events");
@@ -1081,6 +1083,8 @@ async fn responses_websocket_invalid_request_error_with_status_is_forwarded() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submission should succeed while emitting invalid request events");
diff --git a/codex-rs/core/tests/suite/collaboration_instructions.rs b/codex-rs/core/tests/suite/collaboration_instructions.rs
index 81d0678cad..7ff0195655 100644
--- a/codex-rs/core/tests/suite/collaboration_instructions.rs
+++ b/codex-rs/core/tests/suite/collaboration_instructions.rs
@@ -84,6 +84,8 @@ async fn no_collaboration_instructions_by_default() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -143,6 +145,8 @@ async fn user_input_includes_collaboration_instructions_after_override() -> Resu
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -240,6 +244,8 @@ async fn override_then_next_turn_uses_updated_collaboration_instructions() -> Re
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -362,6 +368,8 @@ async fn collaboration_mode_update_emits_new_instruction_message() -> Result<()>
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -389,6 +397,8 @@ async fn collaboration_mode_update_emits_new_instruction_message() -> Result<()>
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -445,6 +455,8 @@ async fn collaboration_mode_update_noop_does_not_append() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -472,6 +484,8 @@ async fn collaboration_mode_update_noop_does_not_append() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -530,6 +544,8 @@ async fn collaboration_mode_update_emits_new_instruction_message_when_mode_chang
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -560,6 +576,8 @@ async fn collaboration_mode_update_emits_new_instruction_message_when_mode_chang
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -619,6 +637,8 @@ async fn collaboration_mode_update_noop_does_not_append_when_mode_is_unchanged()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -649,6 +669,8 @@ async fn collaboration_mode_update_noop_does_not_append_when_mode_is_unchanged()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -712,6 +734,8 @@ async fn resume_replays_collaboration_instructions() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -725,6 +749,8 @@ async fn resume_replays_collaboration_instructions() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -781,6 +807,8 @@ async fn empty_collaboration_instructions_are_ignored() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
diff --git a/codex-rs/core/tests/suite/compact.rs b/codex-rs/core/tests/suite/compact.rs
index f02ab65743..619a325bd0 100644
--- a/codex-rs/core/tests/suite/compact.rs
+++ b/codex-rs/core/tests/suite/compact.rs
@@ -242,6 +242,8 @@ async fn summarize_context_three_requests_and_instructions() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -264,6 +266,8 @@ async fn summarize_context_three_requests_and_instructions() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -440,6 +444,8 @@ async fn manual_compact_uses_custom_prompt() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit first user turn");
@@ -584,6 +590,8 @@ async fn manual_compact_emits_context_compaction_items() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -747,6 +755,8 @@ async fn multiple_auto_compact_per_task_runs_after_token_limit_hit() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit user input");
@@ -1246,6 +1256,8 @@ async fn auto_compact_runs_after_token_limit_hit() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1259,6 +1271,8 @@ async fn auto_compact_runs_after_token_limit_hit() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1272,6 +1286,8 @@ async fn auto_compact_runs_after_token_limit_hit() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1440,6 +1456,8 @@ async fn auto_compact_emits_context_compaction_items() {
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await
             .unwrap();
@@ -1518,6 +1536,8 @@ async fn auto_compact_starts_after_turn_started() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1530,6 +1550,8 @@ async fn auto_compact_starts_after_turn_started() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1542,6 +1564,8 @@ async fn auto_compact_starts_after_turn_started() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2029,6 +2053,8 @@ async fn auto_compact_persists_rollout_entries() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2041,6 +2067,8 @@ async fn auto_compact_persists_rollout_entries() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2053,6 +2081,8 @@ async fn auto_compact_persists_rollout_entries() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2139,6 +2169,8 @@ async fn manual_compact_retries_after_context_window_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2250,6 +2282,8 @@ async fn manual_compact_non_context_failure_retries_then_emits_task_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit user input");
@@ -2342,6 +2376,8 @@ async fn manual_compact_twice_preserves_latest_user_messages() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2357,6 +2393,8 @@ async fn manual_compact_twice_preserves_latest_user_messages() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2372,6 +2410,8 @@ async fn manual_compact_twice_preserves_latest_user_messages() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2533,6 +2573,8 @@ async fn auto_compact_allows_multiple_attempts_when_interleaved_with_other_turn_
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await
             .unwrap();
@@ -2635,6 +2677,8 @@ async fn snapshot_request_shape_mid_turn_continuation_compaction() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -2829,6 +2873,8 @@ async fn auto_compact_counts_encrypted_reasoning_before_last_user() {
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await
             .unwrap();
@@ -2946,6 +2992,8 @@ async fn auto_compact_runs_when_reasoning_header_clears_between_turns() {
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await
             .unwrap();
@@ -3005,6 +3053,8 @@ async fn snapshot_request_shape_pre_turn_compaction_including_incoming_user_mess
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await
             .expect("submit user input");
@@ -3040,6 +3090,8 @@ async fn snapshot_request_shape_pre_turn_compaction_including_incoming_user_mess
                 },
             ],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit user input");
@@ -3250,6 +3302,8 @@ async fn snapshot_request_shape_pre_turn_compaction_context_window_exceeded() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit first user");
@@ -3262,6 +3316,8 @@ async fn snapshot_request_shape_pre_turn_compaction_context_window_exceeded() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit second user");
@@ -3332,6 +3388,8 @@ async fn snapshot_request_shape_manual_compact_without_previous_user_messages()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit follow-up user input");
diff --git a/codex-rs/core/tests/suite/compact_remote.rs b/codex-rs/core/tests/suite/compact_remote.rs
index 96ade23c87..73668a80fb 100644
--- a/codex-rs/core/tests/suite/compact_remote.rs
+++ b/codex-rs/core/tests/suite/compact_remote.rs
@@ -235,6 +235,8 @@ async fn remote_compact_replaces_history_for_followups() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -249,6 +251,8 @@ async fn remote_compact_replaces_history_for_followups() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -379,6 +383,8 @@ async fn remote_compact_runs_automatically() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -453,6 +459,8 @@ async fn remote_compact_trims_function_call_history_to_fit_context_window() -> R
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -464,6 +472,8 @@ async fn remote_compact_trims_function_call_history_to_fit_context_window() -> R
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -573,6 +583,8 @@ async fn auto_remote_compact_trims_function_call_history_to_fit_context_window()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -584,6 +596,8 @@ async fn auto_remote_compact_trims_function_call_history_to_fit_context_window()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -601,6 +615,8 @@ async fn auto_remote_compact_trims_function_call_history_to_fit_context_window()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -698,6 +714,8 @@ async fn auto_remote_compact_failure_stops_agent_loop() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -709,6 +727,8 @@ async fn auto_remote_compact_failure_stops_agent_loop() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -800,6 +820,8 @@ async fn remote_compact_trim_estimate_uses_session_base_instructions() -> Result
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&baseline_codex, |event| {
@@ -814,6 +836,8 @@ async fn remote_compact_trim_estimate_uses_session_base_instructions() -> Result
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&baseline_codex, |event| {
@@ -899,6 +923,8 @@ async fn remote_compact_trim_estimate_uses_session_base_instructions() -> Result
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&override_codex, |event| {
@@ -913,6 +939,8 @@ async fn remote_compact_trim_estimate_uses_session_base_instructions() -> Result
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&override_codex, |event| {
@@ -981,6 +1009,8 @@ async fn remote_manual_compact_emits_context_compaction_items() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -1059,6 +1089,8 @@ async fn remote_manual_compact_failure_emits_task_error_event() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -1141,6 +1173,8 @@ async fn remote_compact_persists_replacement_history_in_rollout() -> Result<()>
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1282,6 +1316,8 @@ async fn remote_compact_and_resume_refresh_stale_developer_instructions() -> Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1297,6 +1333,8 @@ async fn remote_compact_and_resume_refresh_stale_developer_instructions() -> Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1319,6 +1357,8 @@ async fn remote_compact_and_resume_refresh_stale_developer_instructions() -> Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1413,6 +1453,8 @@ async fn remote_compact_refreshes_stale_developer_instructions_without_resume()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1427,6 +1469,8 @@ async fn remote_compact_refreshes_stale_developer_instructions_without_resume()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1496,6 +1540,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_restates_realtime_sta
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1507,6 +1553,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_restates_realtime_sta
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1571,6 +1619,8 @@ async fn remote_request_uses_custom_experimental_realtime_start_instructions() -
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1629,6 +1679,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_restates_realtime_end
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1642,6 +1694,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_restates_realtime_end
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1714,6 +1768,8 @@ async fn snapshot_request_shape_remote_manual_compact_restates_realtime_start()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1728,6 +1784,8 @@ async fn snapshot_request_shape_remote_manual_compact_restates_realtime_start()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1808,6 +1866,8 @@ async fn snapshot_request_shape_remote_mid_turn_compaction_does_not_restate_real
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1821,6 +1881,8 @@ async fn snapshot_request_shape_remote_mid_turn_compaction_does_not_restate_real
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1909,6 +1971,8 @@ async fn snapshot_request_shape_remote_compact_resume_restates_realtime_end() ->
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -1936,6 +2000,8 @@ async fn snapshot_request_shape_remote_compact_resume_restates_realtime_end() ->
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2029,6 +2095,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_including_incoming_us
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await?;
         wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2113,6 +2181,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_strips_incoming_model
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2139,6 +2209,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_strips_incoming_model
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2255,6 +2327,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_context_window_exceed
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2266,6 +2340,8 @@ async fn snapshot_request_shape_remote_pre_turn_compaction_context_window_exceed
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     let error_message = wait_for_event_match(&codex, |event| match event {
@@ -2348,6 +2424,8 @@ async fn snapshot_request_shape_remote_mid_turn_continuation_compaction() -> Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2423,6 +2501,8 @@ async fn snapshot_request_shape_remote_mid_turn_compaction_summary_only_reinject
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2506,6 +2586,8 @@ async fn snapshot_request_shape_remote_mid_turn_compaction_multi_summary_reinjec
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2520,6 +2602,8 @@ async fn snapshot_request_shape_remote_mid_turn_compaction_multi_summary_reinjec
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -2599,6 +2683,8 @@ async fn snapshot_request_shape_remote_manual_compact_without_previous_user_mess
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
diff --git a/codex-rs/core/tests/suite/compact_resume_fork.rs b/codex-rs/core/tests/suite/compact_resume_fork.rs
index fafbced0b7..03d54b2081 100644
--- a/codex-rs/core/tests/suite/compact_resume_fork.rs
+++ b/codex-rs/core/tests/suite/compact_resume_fork.rs
@@ -651,6 +651,8 @@ async fn user_turn(conversation: &Arc<CodexThread>, text: &str) {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .expect("submit user turn");
diff --git a/codex-rs/core/tests/suite/fork_thread.rs b/codex-rs/core/tests/suite/fork_thread.rs
index 96fef440c8..d17e94f033 100644
--- a/codex-rs/core/tests/suite/fork_thread.rs
+++ b/codex-rs/core/tests/suite/fork_thread.rs
@@ -52,6 +52,8 @@ async fn fork_thread_twice_drops_to_first_message() {
                     text_elements: Vec::new(),
                 }],
                 final_output_json_schema: None,
+
+                metadata: None,
             })
             .await
             .unwrap();
diff --git a/codex-rs/core/tests/suite/items.rs b/codex-rs/core/tests/suite/items.rs
index 113a946019..703fd4ea6e 100644
--- a/codex-rs/core/tests/suite/items.rs
+++ b/codex-rs/core/tests/suite/items.rs
@@ -60,6 +60,8 @@ async fn user_message_item_is_emitted() -> anyhow::Result<()> {
         .submit(Op::UserInput {
             items: vec![expected_input.clone()],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -116,6 +118,8 @@ async fn assistant_message_item_is_emitted() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -174,6 +178,8 @@ async fn reasoning_item_is_emitted() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -233,6 +239,8 @@ async fn web_search_item_is_emitted() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -288,6 +296,8 @@ async fn image_generation_call_event_is_emitted() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -341,6 +351,8 @@ async fn image_generation_call_event_is_emitted_when_image_save_fails() -> anyho
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -394,6 +406,8 @@ async fn agent_message_content_delta_has_item_metadata() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -1036,6 +1050,8 @@ async fn reasoning_content_delta_has_item_metadata() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -1095,6 +1111,8 @@ async fn reasoning_raw_content_delta_respects_flag() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
diff --git a/codex-rs/core/tests/suite/model_visible_layout.rs b/codex-rs/core/tests/suite/model_visible_layout.rs
index 587436c83b..37b4990cb7 100644
--- a/codex-rs/core/tests/suite/model_visible_layout.rs
+++ b/codex-rs/core/tests/suite/model_visible_layout.rs
@@ -318,6 +318,8 @@ async fn snapshot_model_visible_layout_resume_with_personality_change() -> Resul
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -416,6 +418,8 @@ async fn snapshot_model_visible_layout_resume_override_matches_rollout_model() -
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -461,6 +465,8 @@ async fn snapshot_model_visible_layout_resume_override_matches_rollout_model() -
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |event| {
diff --git a/codex-rs/core/tests/suite/otel.rs b/codex-rs/core/tests/suite/otel.rs
index c96988d18b..e36990024b 100644
--- a/codex-rs/core/tests/suite/otel.rs
+++ b/codex-rs/core/tests/suite/otel.rs
@@ -107,6 +107,8 @@ async fn responses_api_emits_api_request_event() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -150,6 +152,8 @@ async fn process_sse_emits_tracing_for_output_item() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -193,6 +197,8 @@ async fn process_sse_emits_failed_event_on_parse_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -237,6 +243,8 @@ async fn process_sse_records_failed_event_when_stream_closes_without_completed()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -301,6 +309,8 @@ async fn process_sse_failed_event_records_response_error_message() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -363,6 +373,8 @@ async fn process_sse_failed_event_logs_parse_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -412,6 +424,8 @@ async fn process_sse_failed_event_logs_missing_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -470,6 +484,8 @@ async fn process_sse_failed_event_logs_response_completed_parse_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -522,6 +538,8 @@ async fn process_sse_emits_completed_telemetry() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -594,6 +612,8 @@ async fn handle_responses_span_records_response_kind_and_tool_name() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -678,6 +698,8 @@ async fn record_responses_sets_span_fields_for_response_events() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -762,6 +784,8 @@ async fn handle_response_item_records_tool_result_for_custom_tool_call() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -835,6 +859,8 @@ async fn handle_response_item_records_tool_result_for_function_call() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -918,6 +944,8 @@ async fn handle_response_item_records_tool_result_for_local_shell_missing_ids()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -985,6 +1013,8 @@ async fn handle_response_item_records_tool_result_for_local_shell_call() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1093,6 +1123,8 @@ async fn handle_container_exec_autoapprove_from_config_records_tool_decision() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1144,6 +1176,8 @@ async fn handle_container_exec_user_approved_records_tool_decision() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1210,6 +1244,8 @@ async fn handle_container_exec_user_approved_for_session_records_tool_decision()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1276,6 +1312,8 @@ async fn handle_sandbox_error_user_approves_retry_records_tool_decision() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1342,6 +1380,8 @@ async fn handle_container_exec_user_denies_records_tool_decision() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1408,6 +1448,8 @@ async fn handle_sandbox_error_user_approves_for_session_records_tool_decision()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -1475,6 +1517,8 @@ async fn handle_sandbox_error_user_denies_records_tool_decision() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/pending_input.rs b/codex-rs/core/tests/suite/pending_input.rs
index 30b0d9d50b..dbd28caeaf 100644
--- a/codex-rs/core/tests/suite/pending_input.rs
+++ b/codex-rs/core/tests/suite/pending_input.rs
@@ -104,6 +104,8 @@ async fn injected_user_input_triggers_follow_up_request_with_deltas() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -120,6 +122,8 @@ async fn injected_user_input_triggers_follow_up_request_with_deltas() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/permissions_messages.rs b/codex-rs/core/tests/suite/permissions_messages.rs
index cdf69acdc0..430c4e1939 100644
--- a/codex-rs/core/tests/suite/permissions_messages.rs
+++ b/codex-rs/core/tests/suite/permissions_messages.rs
@@ -66,6 +66,8 @@ async fn permissions_message_sent_once_on_start() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -107,6 +109,8 @@ async fn permissions_message_added_on_override_change() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -134,6 +138,8 @@ async fn permissions_message_added_on_override_change() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -181,6 +187,8 @@ async fn permissions_message_not_added_when_no_change() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -192,6 +200,8 @@ async fn permissions_message_not_added_when_no_change() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -250,6 +260,8 @@ async fn resume_replays_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -279,6 +291,8 @@ async fn resume_replays_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -292,6 +306,8 @@ async fn resume_replays_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -351,6 +367,8 @@ async fn resume_and_fork_append_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -380,6 +398,8 @@ async fn resume_and_fork_append_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&initial.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -401,6 +421,8 @@ async fn resume_and_fork_append_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -429,6 +451,8 @@ async fn resume_and_fork_append_permissions_messages() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&forked.thread, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -483,6 +507,8 @@ async fn permissions_message_includes_writable_roots() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
diff --git a/codex-rs/core/tests/suite/plugins.rs b/codex-rs/core/tests/suite/plugins.rs
index 0eba6e3234..cd6b19fe80 100644
--- a/codex-rs/core/tests/suite/plugins.rs
+++ b/codex-rs/core/tests/suite/plugins.rs
@@ -213,6 +213,8 @@ async fn capability_sections_render_in_developer_message_in_order() -> Result<()
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -288,6 +290,8 @@ async fn explicit_plugin_mentions_inject_plugin_guidance() -> Result<()> {
                 path: format!("plugin://{SAMPLE_PLUGIN_CONFIG_NAME}"),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -360,6 +364,8 @@ async fn explicit_plugin_mentions_track_plugin_used_analytics() -> Result<()> {
                 path: format!("plugin://{SAMPLE_PLUGIN_CONFIG_NAME}"),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
diff --git a/codex-rs/core/tests/suite/prompt_caching.rs b/codex-rs/core/tests/suite/prompt_caching.rs
index 96b7f64570..1360cb538a 100644
--- a/codex-rs/core/tests/suite/prompt_caching.rs
+++ b/codex-rs/core/tests/suite/prompt_caching.rs
@@ -151,6 +151,8 @@ async fn prompt_tools_are_consistent_across_requests() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -162,6 +164,8 @@ async fn prompt_tools_are_consistent_across_requests() -> anyhow::Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -247,6 +251,8 @@ async fn gpt_5_tools_without_apply_patch_append_apply_patch_instructions() -> an
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -258,6 +264,8 @@ async fn gpt_5_tools_without_apply_patch_append_apply_patch_instructions() -> an
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -320,6 +328,8 @@ async fn prefixes_context_and_instructions_once_and_consistently_across_requests
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -331,6 +341,8 @@ async fn prefixes_context_and_instructions_once_and_consistently_across_requests
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -412,6 +424,8 @@ async fn overrides_turn_context_but_keeps_cached_prefix_and_key_constant() -> an
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -448,6 +462,8 @@ async fn overrides_turn_context_but_keeps_cached_prefix_and_key_constant() -> an
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
@@ -530,6 +546,8 @@ async fn override_before_first_turn_emits_environment_context() -> anyhow::Resul
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -681,6 +699,8 @@ async fn per_turn_overrides_keep_cached_prefix_and_key_constant() -> anyhow::Res
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
diff --git a/codex-rs/core/tests/suite/quota_exceeded.rs b/codex-rs/core/tests/suite/quota_exceeded.rs
index 466680e6a8..8c3cbe89df 100644
--- a/codex-rs/core/tests/suite/quota_exceeded.rs
+++ b/codex-rs/core/tests/suite/quota_exceeded.rs
@@ -46,6 +46,8 @@ async fn quota_exceeded_emits_single_error_event() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/realtime_conversation.rs b/codex-rs/core/tests/suite/realtime_conversation.rs
index 06cb31630a..6509d61801 100644
--- a/codex-rs/core/tests/suite/realtime_conversation.rs
+++ b/codex-rs/core/tests/suite/realtime_conversation.rs
@@ -2036,6 +2036,8 @@ async fn inbound_handoff_request_steers_active_turn() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
diff --git a/codex-rs/core/tests/suite/request_compression.rs b/codex-rs/core/tests/suite/request_compression.rs
index 7f8b996c08..3fb3dbbae1 100644
--- a/codex-rs/core/tests/suite/request_compression.rs
+++ b/codex-rs/core/tests/suite/request_compression.rs
@@ -45,6 +45,8 @@ async fn request_body_is_zstd_compressed_for_codex_backend_when_enabled() -> any
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -92,6 +94,8 @@ async fn request_body_is_not_compressed_for_api_key_auth_even_when_enabled() ->
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
diff --git a/codex-rs/core/tests/suite/resume.rs b/codex-rs/core/tests/suite/resume.rs
index a77ad60b5a..a4e9f14d3d 100644
--- a/codex-rs/core/tests/suite/resume.rs
+++ b/codex-rs/core/tests/suite/resume.rs
@@ -91,6 +91,8 @@ async fn resume_includes_initial_messages_from_rollout_events() -> Result<()> {
                 text_elements: text_elements.clone(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -176,6 +178,8 @@ async fn resume_includes_initial_messages_from_reasoning_events() -> Result<()>
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
@@ -265,6 +269,8 @@ async fn resume_switches_models_preserves_base_instructions() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -305,6 +311,8 @@ async fn resume_switches_models_preserves_base_instructions() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |event| {
@@ -320,6 +328,8 @@ async fn resume_switches_models_preserves_base_instructions() -> Result<()> {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |event| {
@@ -390,6 +400,8 @@ async fn resume_model_switch_is_not_duplicated_after_pre_turn_override() -> Resu
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
@@ -433,6 +445,8 @@ async fn resume_model_switch_is_not_duplicated_after_pre_turn_override() -> Resu
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&resumed.codex, |event| {
diff --git a/codex-rs/core/tests/suite/review.rs b/codex-rs/core/tests/suite/review.rs
index 81d3d1e6da..ba37377f2c 100644
--- a/codex-rs/core/tests/suite/review.rs
+++ b/codex-rs/core/tests/suite/review.rs
@@ -717,6 +717,8 @@ async fn review_history_surfaces_in_parent_session() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/search_tool.rs b/codex-rs/core/tests/suite/search_tool.rs
index dd182befb5..09c8e59bb0 100644
--- a/codex-rs/core/tests/suite/search_tool.rs
+++ b/codex-rs/core/tests/suite/search_tool.rs
@@ -380,6 +380,8 @@ async fn tool_search_returns_deferred_tools_without_follow_up_tool_injection() -
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
 
diff --git a/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs b/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs
index 23ffc4afb0..4fdb62f414 100644
--- a/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs
+++ b/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs
@@ -97,6 +97,8 @@ async fn continue_after_stream_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
@@ -116,6 +118,8 @@ async fn continue_after_stream_error() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/stream_no_completed.rs b/codex-rs/core/tests/suite/stream_no_completed.rs
index 5d1b214811..dece9f2579 100644
--- a/codex-rs/core/tests/suite/stream_no_completed.rs
+++ b/codex-rs/core/tests/suite/stream_no_completed.rs
@@ -81,6 +81,8 @@ async fn retries_on_early_close() {
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await
         .unwrap();
diff --git a/codex-rs/core/tests/suite/user_notification.rs b/codex-rs/core/tests/suite/user_notification.rs
index a2303c0ecf..bcf54484c7 100644
--- a/codex-rs/core/tests/suite/user_notification.rs
+++ b/codex-rs/core/tests/suite/user_notification.rs
@@ -62,6 +62,8 @@ mv "${tmp_path}" "${payload_path}""#,
                 text_elements: Vec::new(),
             }],
             final_output_json_schema: None,
+
+            metadata: None,
         })
         .await?;
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index beccedb781..51001828bf 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -3,6 +3,7 @@
 //! Uses a SQ (Submission Queue) / EQ (Event Queue) pattern to asynchronously communicate
 //! between user and agent.
 
+use std::collections::BTreeMap;
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::ffi::OsStr;
@@ -238,6 +239,9 @@ pub enum Op {
         /// Optional JSON Schema used to constrain the final assistant message for this turn.
         #[serde(skip_serializing_if = "Option::is_none")]
         final_output_json_schema: Option<Value>,
+        /// Optional metadata attached only to this turn.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        metadata: Option<BTreeMap<String, String>>,
     },
 
     /// Similar to [`Op::UserInput`], but contains additional context required
@@ -4256,6 +4260,7 @@ mod tests {
         let op = Op::UserInput {
             items: Vec::new(),
             final_output_json_schema: None,
+            metadata: None,
         };
 
         let json_op = serde_json::to_value(op)?;
@@ -4273,6 +4278,7 @@ mod tests {
             Op::UserInput {
                 items: Vec::new(),
                 final_output_json_schema: None,
+                metadata: None,
             }
         );
 
@@ -4292,6 +4298,7 @@ mod tests {
         let op = Op::UserInput {
             items: Vec::new(),
             final_output_json_schema: Some(schema.clone()),
+            metadata: None,
         };
 
         let json_op = serde_json::to_value(op)?;