Expose conversation history to extension tools (#23963)

## Why

Extension tools that need conversation context should be able to read it
from the live tool invocation instead of reaching into thread
persistence themselves.

## What changed

- Add a `ConversationHistory` snapshot to extension `ToolCall`s and
populate it from the current raw in-memory response history.
- Expose all history items at this boundary so each extension can filter
and bound the subset it needs before consuming or forwarding it.
- Cover the adapter and registry dispatch paths and update existing
extension tests that construct `ToolCall` literals.

## Test plan

- `cargo test -p codex-tools`
- `cargo test -p codex-extension-api`
- `cargo test -p codex-goal-extension`
- `cargo test -p codex-memories-extension`
- `cargo test -p codex-core passes_turn_fields_to_extension_call`
- `cargo test -p codex-core
extension_tool_executors_are_model_visible_and_dispatchable`

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

@@ -126,6 +126,11 @@ impl ContextManager {
         &self.items
     }
 
+    /// Returns raw items in the history and consumes the snapshot.
+    pub(crate) fn into_raw_items(self) -> Vec<ResponseItem> {
+        self.items
+    }
+
     pub(crate) fn history_version(&self) -> u64 {
         self.history_version
     }

codex-rs/core/src/tools/handlers/extension_tools.rs

@@ -1,5 +1,6 @@
 use std::sync::Arc;
 
+use codex_tools::ConversationHistory;
 use codex_tools::ToolCall as ExtensionToolCall;
 use codex_tools::ToolName;
 use codex_tools::ToolSpec;
@@ -53,7 +54,7 @@ impl ToolExecutor<ToolInvocation> for ExtensionToolAdapter {
         &self,
         invocation: ToolInvocation,
     ) -> Result<Box<dyn ToolOutput>, FunctionCallError> {
-        self.0.handle(to_extension_call(&invocation)).await
+        self.0.handle(to_extension_call(&invocation).await).await
     }
 }
 
@@ -86,12 +87,15 @@ impl CoreToolRuntime for ExtensionToolAdapter {
     }
 }
 
-fn to_extension_call(invocation: &ToolInvocation) -> ExtensionToolCall {
+async fn to_extension_call(invocation: &ToolInvocation) -> ExtensionToolCall {
+    let conversation_history =
+        ConversationHistory::new(invocation.session.clone_history().await.into_raw_items());
     ExtensionToolCall {
         turn_id: invocation.turn.sub_id.clone(),
         call_id: invocation.call_id.clone(),
         tool_name: invocation.tool_name.clone(),
         truncation_policy: invocation.turn.truncation_policy,
+        conversation_history,
         payload: invocation.payload.clone(),
     }
 }
@@ -108,6 +112,8 @@ fn extension_tool_hook_input(arguments: &str) -> Value {
 mod tests {
     use std::sync::Arc;
 
+    use codex_protocol::models::ContentItem;
+    use codex_protocol::models::ResponseItem;
     use pretty_assertions::assert_eq;
     use serde_json::json;
     use tokio::sync::Mutex;
@@ -236,6 +242,17 @@ mod tests {
         let (session, turn) = crate::session::tests::make_session_and_context().await;
         let turn_id = turn.sub_id.clone();
         let truncation_policy = turn.truncation_policy;
+        let history_item = ResponseItem::Message {
+            id: None,
+            role: "user".to_string(),
+            content: vec![ContentItem::InputText {
+                text: "extension history".to_string(),
+            }],
+            phase: None,
+        };
+        session
+            .record_into_history(std::slice::from_ref(&history_item), &turn)
+            .await;
         let invocation = ToolInvocation {
             session: session.into(),
             turn: turn.into(),
@@ -261,6 +278,10 @@ mod tests {
             codex_tools::ToolName::plain("extension_echo")
         );
         assert_eq!(captured_call.truncation_policy, truncation_policy);
+        assert_eq!(
+            captured_call.conversation_history.items(),
+            std::slice::from_ref(&history_item)
+        );
         match captured_call.payload {
             ToolPayload::Function { arguments } => {
                 assert_eq!(arguments, json!({ "message": "hello" }).to_string());

codex-rs/core/src/tools/router_tests.rs

@@ -11,6 +11,7 @@ use codex_extension_api::ResponsesApiTool;
 use codex_extension_api::ToolCall as ExtensionToolCall;
 use codex_extension_api::ToolExecutor;
 use codex_protocol::dynamic_tools::DynamicToolSpec;
+use codex_protocol::models::ContentItem;
 use codex_protocol::models::FunctionCallOutputBody;
 use codex_protocol::models::ResponseInputItem;
 use codex_protocol::models::ResponseItem;
@@ -81,6 +82,7 @@ impl ToolExecutor<ExtensionToolCall> for ExtensionEchoExecutor {
         Ok(Box::new(codex_tools::JsonToolOutput::new(json!({
             "arguments": arguments,
             "callId": call.call_id,
+            "conversationHistory": call.conversation_history.items(),
             "ok": true,
         }))))
     }
@@ -327,6 +329,17 @@ fn mcp_tool_info(
 async fn extension_tool_executors_are_model_visible_and_dispatchable() -> anyhow::Result<()> {
     let (mut session, turn) = make_session_and_context().await;
     session.services.extensions = extension_tool_test_registry();
+    let history_item = ResponseItem::Message {
+        id: None,
+        role: "user".to_string(),
+        content: vec![ContentItem::InputText {
+            text: "extension history".to_string(),
+        }],
+        phase: None,
+    };
+    session
+        .record_into_history(std::slice::from_ref(&history_item), &turn)
+        .await;
 
     let router = ToolRouter::from_turn_context(
         &turn,
@@ -384,6 +397,7 @@ async fn extension_tool_executors_are_model_visible_and_dispatchable() -> anyhow
                 json!({
                     "arguments": { "message": "hello" },
                     "callId": "call-extension",
+                    "conversationHistory": [history_item],
                     "ok": true,
                 })
             );

codex-rs/ext/extension-api/src/lib.rs

@@ -10,6 +10,7 @@ pub use capabilities::NoopExtensionEventSink;
 pub use capabilities::NoopResponseItemInjector;
 pub use capabilities::ResponseItemInjectionFuture;
 pub use capabilities::ResponseItemInjector;
+pub use codex_tools::ConversationHistory;
 pub use codex_tools::FunctionCallError;
 pub use codex_tools::JsonToolOutput;
 pub use codex_tools::ResponsesApiTool;

codex-rs/ext/goal/tests/goal_extension_backend.rs

@@ -625,6 +625,7 @@ fn tool_call(tool_name: &str, call_id: &str, arguments: serde_json::Value) -> To
         call_id: call_id.to_string(),
         tool_name: codex_extension_api::ToolName::plain(tool_name),
         truncation_policy: TruncationPolicy::Bytes(1024),
+        conversation_history: codex_extension_api::ConversationHistory::default(),
         payload: ToolPayload::Function {
             arguments: arguments.to_string(),
         },

codex-rs/ext/memories/src/tests.rs

@@ -139,6 +139,7 @@ async fn read_tool_reads_memory_file() {
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::READ_TOOL_NAME),
             truncation_policy: TruncationPolicy::Bytes(1024),
+            conversation_history: codex_extension_api::ConversationHistory::default(),
             payload: payload.clone(),
         })
         .await
@@ -183,6 +184,7 @@ async fn search_tool_accepts_multiple_queries() {
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
             truncation_policy: TruncationPolicy::Bytes(1024),
+            conversation_history: codex_extension_api::ConversationHistory::default(),
             payload: payload.clone(),
         })
         .await
@@ -253,6 +255,7 @@ async fn search_tool_accepts_windowed_all_match_mode() {
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
             truncation_policy: TruncationPolicy::Bytes(1024),
+            conversation_history: codex_extension_api::ConversationHistory::default(),
             payload: payload.clone(),
         })
         .await
@@ -303,6 +306,7 @@ async fn search_tool_rejects_legacy_single_query() {
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
             truncation_policy: TruncationPolicy::Bytes(1024),
+            conversation_history: codex_extension_api::ConversationHistory::default(),
             payload,
         })
         .await;

codex-rs/tools/src/lib.rs

@@ -57,6 +57,7 @@ pub use responses_api::dynamic_tool_to_responses_api_tool;
 pub use responses_api::mcp_tool_to_deferred_responses_api_tool;
 pub use responses_api::mcp_tool_to_responses_api_tool;
 pub use responses_api::tool_definition_to_responses_api_tool;
+pub use tool_call::ConversationHistory;
 pub use tool_call::ToolCall;
 pub use tool_config::ShellCommandBackendConfig;
 pub use tool_config::ToolEnvironmentMode;

codex-rs/tools/src/tool_call.rs

@@ -1,7 +1,27 @@
 use crate::FunctionCallError;
 use crate::ToolName;
 use crate::ToolPayload;
+use codex_protocol::models::ResponseItem;
 use codex_utils_output_truncation::TruncationPolicy;
+use std::sync::Arc;
+
+/// Raw response history snapshot available when an extension tool is invoked.
+#[derive(Clone, Debug, Default)]
+pub struct ConversationHistory {
+    items: Arc<[ResponseItem]>,
+}
+
+impl ConversationHistory {
+    pub fn new(items: Vec<ResponseItem>) -> Self {
+        Self {
+            items: items.into(),
+        }
+    }
+
+    pub fn items(&self) -> &[ResponseItem] {
+        &self.items
+    }
+}
 
 // TODO: this is temporary and will disappear in the next PR (as we make codex-extension-api generic on Invocation.
 #[derive(Clone, Debug)]
@@ -10,6 +30,7 @@ pub struct ToolCall {
     pub call_id: String,
     pub tool_name: ToolName,
     pub truncation_policy: TruncationPolicy,
+    pub conversation_history: ConversationHistory,
     pub payload: ToolPayload,
 }