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/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;