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/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,
                 })
             );