Include code-mode tool names in Responses Lite metadata (#35271)

## What changed

- Add `code_mode_tool_names` to Responses Lite turn metadata, mapping each normalized code-mode identifier to its structured `ToolName`.
- Reserve the metadata key against client overrides and omit it from metadata exposed to external MCP servers.
- Keep non-Lite requests and the legacy top-level client metadata unchanged.

## Testing

- Cover HTTP and WebSocket Responses Lite requests, including switching from a non-Lite model.
- Verify reserved-key handling and external MCP metadata filtering.

GitOrigin-RevId: b678afba13d57a91e26f5895aa37238fbb4cb276

codex-rs/core/src/responses_metadata.rs

@@ -7,6 +7,7 @@ use codex_analytics::CompactionReason;
 use codex_analytics::CompactionStrategy;
 use codex_analytics::CompactionTrigger;
 use codex_protocol::ThreadId;
+use codex_protocol::ToolName;
 use codex_protocol::protocol::InternalSessionSource;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::SubAgentSource;
@@ -30,6 +31,7 @@ pub(crate) const TURN_ID_KEY: &str = "turn_id";
 pub(crate) const WINDOW_ID_KEY: &str = "window_id";
 pub(crate) const REQUEST_KIND_KEY: &str = "request_kind";
 pub(crate) const COMPACTION_KEY: &str = "compaction";
+pub(crate) const CODE_MODE_TOOL_NAMES_KEY: &str = "code_mode_tool_names";
 pub(crate) const TURN_STARTED_AT_UNIX_MS_KEY: &str = "turn_started_at_unix_ms";
 
 pub(crate) const FORKED_FROM_THREAD_ID_KEY: &str = "forked_from_thread_id";
@@ -54,6 +56,7 @@ const RESERVED_METADATA_KEYS: &[&str] = &[
     X_OPENAI_SUBAGENT_HEADER,
     REQUEST_KIND_KEY,
     COMPACTION_KEY,
+    CODE_MODE_TOOL_NAMES_KEY,
     TURN_STARTED_AT_UNIX_MS_KEY,
     FORKED_FROM_THREAD_ID_KEY,
     PARENT_THREAD_ID_KEY,
@@ -165,6 +168,7 @@ pub struct CodexResponsesMetadata {
     pub(crate) thread_source: Option<ThreadSource>,
     pub(crate) sandbox: Option<String>,
     pub(crate) workspaces: BTreeMap<String, TurnMetadataWorkspace>,
+    pub(crate) code_mode_tool_names: Option<BTreeMap<String, ToolName>>,
     pub(crate) turn_started_at_unix_ms: Option<i64>,
     pub(crate) extra: BTreeMap<String, String>,
 }
@@ -190,6 +194,7 @@ impl CodexResponsesMetadata {
             thread_source: None,
             sandbox: None,
             workspaces: BTreeMap::new(),
+            code_mode_tool_names: None,
             turn_started_at_unix_ms: None,
             extra: BTreeMap::new(),
         }
@@ -292,6 +297,7 @@ impl CodexResponsesMetadata {
             thread_source: self.thread_source.as_ref(),
             sandbox: self.sandbox.as_deref(),
             workspaces: non_empty_workspaces(&self.workspaces),
+            code_mode_tool_names: self.code_mode_tool_names.as_ref(),
             turn_started_at_unix_ms: self.turn_started_at_unix_ms,
             compaction,
             // responsesapi_client_metadata enriches the Codex turn metadata blob, not literal
@@ -382,6 +388,8 @@ struct CodexTurnMetadataPayload<'a> {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     workspaces: Option<&'a BTreeMap<String, TurnMetadataWorkspace>>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
+    code_mode_tool_names: Option<&'a BTreeMap<String, ToolName>>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
     turn_started_at_unix_ms: Option<i64>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     compaction: Option<CompactionTurnMetadata>,