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/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,
 }