Reduce cloning when building Responses requests (#34825)

## Why

Preparing Responses API requests rebuilt tool definitions as a generic JSON
tree, and incremental WebSocket requests cloned their full item prefix for
comparison.

## What changed

- Serialize tool definitions into shared raw JSON that can be embedded directly
  in HTTP and WebSocket requests.
- Compare incremental request prefixes in place while still ignoring internal
  message metadata.

## Testing

- Verify raw tool JSON matches the existing value encoding.
- Preserve the serialized WebSocket request payload.

GitOrigin-RevId: 66e2921792c332e8904954dafa597f6d39abcf29

codex-rs/tools/Cargo.toml

@@ -26,7 +26,7 @@ rmcp = { workspace = true, default-features = false, features = [
     "server",
 ] }
 serde = { workspace = true, features = ["derive"] }
-serde_json = { workspace = true }
+serde_json = { workspace = true, features = ["raw_value"] }
 thiserror = { workspace = true }
 tracing = { workspace = true }
 urlencoding = { workspace = true }

codex-rs/tools/src/lib.rs

@@ -105,3 +105,4 @@ pub use tool_spec::ResponsesApiWebSearchFilters;
 pub use tool_spec::ResponsesApiWebSearchUserLocation;
 pub use tool_spec::ToolSpec;
 pub use tool_spec::create_tools_json_for_responses_api;
+pub use tool_spec::create_tools_raw_json_for_responses_api;

codex-rs/tools/src/tool_spec.rs

@@ -9,6 +9,8 @@ use codex_protocol::config_types::WebSearchUserLocation as ConfigWebSearchUserLo
 use codex_protocol::config_types::WebSearchUserLocationType;
 use serde::Serialize;
 use serde_json::Value;
+use serde_json::value::RawValue;
+use std::sync::Arc;
 
 /// When serialized as JSON, this produces a valid "Tool" in the OpenAI
 /// Responses API.
@@ -87,6 +89,13 @@ pub fn create_tools_json_for_responses_api(
     Ok(tools_json)
 }
 
+/// Returns raw JSON that can be embedded directly in a Responses API request.
+pub fn create_tools_raw_json_for_responses_api(
+    tools: &[ToolSpec],
+) -> Result<Arc<RawValue>, serde_json::Error> {
+    serde_json::value::to_raw_value(tools).map(Arc::from)
+}
+
 #[derive(Debug, Clone, Serialize, PartialEq)]
 pub struct ResponsesApiWebSearchFilters {
     #[serde(skip_serializing_if = "Option::is_none")]

codex-rs/tools/src/tool_spec_tests.rs

@@ -9,6 +9,7 @@ use crate::JsonSchema;
 use crate::ResponsesApiNamespaceTool;
 use crate::ResponsesApiTool;
 use crate::create_tools_json_for_responses_api;
+use crate::create_tools_raw_json_for_responses_api;
 use codex_protocol::config_types::WebSearchContextSize;
 use codex_protocol::config_types::WebSearchFilters as ConfigWebSearchFilters;
 use codex_protocol::config_types::WebSearchUserLocation as ConfigWebSearchUserLocation;
@@ -143,6 +144,29 @@ fn create_tools_json_for_responses_api_includes_top_level_name() {
     );
 }
 
+#[test]
+fn raw_tool_json_matches_value_encoding() {
+    let specs = vec![ToolSpec::Function(ResponsesApiTool {
+        name: "demo".to_string(),
+        description: "A demo tool".to_string(),
+        strict: false,
+        defer_loading: None,
+        parameters: JsonSchema::object(
+            BTreeMap::new(),
+            /*required*/ None,
+            /*additional_properties*/ None,
+        ),
+        output_schema: None,
+    })];
+    let expected = create_tools_json_for_responses_api(&specs).expect("serialize tools");
+    let raw = create_tools_raw_json_for_responses_api(&specs).expect("serialize raw tools");
+
+    assert_eq!(
+        serde_json::from_str::<Vec<serde_json::Value>>(raw.get()).expect("parse raw tools"),
+        expected,
+    );
+}
+
 #[test]
 fn namespace_tool_spec_serializes_expected_wire_shape() {
     assert_eq!(