codex-tools: extract responses API tool models (#16031)

## Why

The previous extraction steps moved shared tool-schema parsing into
`codex-tools`, but `codex-core` still owned the generic Responses API
tool models and the last adapter layer that turned parsed tool
definitions into `ResponsesApiTool` values.

That left `core/src/tools/spec.rs` and `core/src/client_common.rs`
holding a chunk of tool-shaping code that does not need session state,
runtime plumbing, or any other `codex-core`-specific dependency. As a
result, `codex-tools` owned the parsed tool definition, but `codex-core`
still owned the generic wire model that those definitions are converted
into.

This change moves that boundary one step further. `codex-tools` now owns
the reusable Responses/tool wire structs and the shared conversion
helpers for dynamic tools, MCP tools, and deferred MCP aliases.
`codex-core` continues to own `ToolSpec` orchestration and the remaining
web-search-specific request shapes.

## What changed

- added `tools/src/responses_api.rs` to own `ResponsesApiTool`,
`FreeformTool`, `ToolSearchOutputTool`, namespace output types, and the
shared `ToolDefinition -> ResponsesApiTool` adapter helpers
- added `tools/src/responses_api_tests.rs` for deferred-loading
behavior, adapter coverage, and namespace serialization coverage
- rewired `core/src/tools/spec.rs` to use the extracted dynamic/MCP
adapter helpers instead of defining those conversions locally
- rewired `core/src/tools/handlers/tool_search.rs` to use the extracted
deferred MCP adapter and namespace output types directly
- slimmed `core/src/client_common.rs` so it now keeps `ToolSpec` and the
web-search-specific wire types, while reusing the extracted tool models
from `codex-tools`
- moved the extracted seam tests out of `core` and updated
`codex-rs/tools/README.md` plus `tools/src/lib.rs` to reflect the
expanded `codex-tools` boundary

## Test plan

- `cargo test -p codex-tools`
- `cargo test -p codex-core --lib tools::spec::`
- `cargo test -p codex-core --lib tools::handlers::tool_search::`
- `just fix -p codex-tools -p codex-core`
- `just argument-comment-lint`

## References

- [#15923](https://github.com/openai/codex/pull/15923) `codex-tools:
extract shared tool schema parsing`
- [#15928](https://github.com/openai/codex/pull/15928) `codex-tools:
extract MCP schema adapters`
- [#15944](https://github.com/openai/codex/pull/15944) `codex-tools:
extract dynamic tool adapters`
- [#15953](https://github.com/openai/codex/pull/15953) `codex-tools:
introduce named tool definitions`

codex-rs/core/src/tools/handlers/tool_search.rs

@@ -1,6 +1,3 @@
-use crate::client_common::tools::ResponsesApiNamespace;
-use crate::client_common::tools::ResponsesApiNamespaceTool;
-use crate::client_common::tools::ToolSearchOutputTool;
 use crate::function_tool::FunctionCallError;
 use crate::mcp_connection_manager::ToolInfo;
 use crate::tools::context::ToolInvocation;
@@ -8,17 +5,17 @@ use crate::tools::context::ToolPayload;
 use crate::tools::context::ToolSearchOutput;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use crate::tools::spec::mcp_tool_to_deferred_openai_tool;
 use async_trait::async_trait;
 use bm25::Document;
 use bm25::Language;
 use bm25::SearchEngineBuilder;
+use codex_tools::ResponsesApiNamespace;
+use codex_tools::ResponsesApiNamespaceTool;
+use codex_tools::ToolSearchOutputTool;
+use codex_tools::mcp_tool_to_deferred_responses_api_tool;
 use std::collections::BTreeMap;
 use std::collections::HashMap;
 
-#[cfg(test)]
-use crate::client_common::tools::ResponsesApiTool;
-
 pub struct ToolSearchHandler {
     tools: HashMap<String, ToolInfo>,
 }
@@ -129,7 +126,7 @@ fn serialize_tool_search_output_tools(
         let tools = tools
             .iter()
             .map(|tool| {
-                mcp_tool_to_deferred_openai_tool(tool.tool_name.clone(), tool.tool.clone())
+                mcp_tool_to_deferred_responses_api_tool(tool.tool_name.clone(), &tool.tool)
                     .map(ResponsesApiNamespaceTool::Function)
             })
             .collect::<Result<Vec<_>, _>>()?;

codex-rs/core/src/tools/handlers/tool_search_tests.rs

@@ -1,5 +1,6 @@
 use super::*;
 use crate::mcp::CODEX_APPS_MCP_SERVER_NAME;
+use codex_tools::ResponsesApiTool;
 use pretty_assertions::assert_eq;
 use rmcp::model::JsonObject;
 use rmcp::model::Tool;

codex-rs/core/src/tools/spec.rs

@@ -1,6 +1,3 @@
-use crate::client_common::tools::FreeformTool;
-use crate::client_common::tools::FreeformToolFormat;
-use crate::client_common::tools::ResponsesApiTool;
 use crate::client_common::tools::ToolSpec;
 use crate::config::AgentRoleConfig;
 use crate::mcp::CODEX_APPS_MCP_SERVER_NAME;
@@ -46,9 +43,11 @@ use codex_protocol::openai_models::WebSearchToolType;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::SubAgentSource;
-use codex_tools::ToolDefinition;
-use codex_tools::parse_dynamic_tool;
-use codex_tools::parse_mcp_tool;
+use codex_tools::FreeformTool;
+use codex_tools::FreeformToolFormat;
+use codex_tools::ResponsesApiTool;
+use codex_tools::dynamic_tool_to_responses_api_tool;
+use codex_tools::mcp_tool_to_responses_api_tool;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_template::Template;
 use serde::Deserialize;
@@ -2382,41 +2381,6 @@ fn push_tool_spec(
     }
 }
 
-pub(crate) fn mcp_tool_to_openai_tool(
-    fully_qualified_name: String,
-    tool: rmcp::model::Tool,
-) -> Result<ResponsesApiTool, serde_json::Error> {
-    Ok(tool_definition_to_openai_tool(
-        parse_mcp_tool(&tool)?.renamed(fully_qualified_name),
-    ))
-}
-
-pub(crate) fn mcp_tool_to_deferred_openai_tool(
-    name: String,
-    tool: rmcp::model::Tool,
-) -> Result<ResponsesApiTool, serde_json::Error> {
-    Ok(tool_definition_to_openai_tool(
-        parse_mcp_tool(&tool)?.renamed(name).into_deferred(),
-    ))
-}
-
-fn dynamic_tool_to_openai_tool(
-    tool: &DynamicToolSpec,
-) -> Result<ResponsesApiTool, serde_json::Error> {
-    Ok(tool_definition_to_openai_tool(parse_dynamic_tool(tool)?))
-}
-
-fn tool_definition_to_openai_tool(tool_definition: ToolDefinition) -> ResponsesApiTool {
-    ResponsesApiTool {
-        name: tool_definition.name,
-        description: tool_definition.description,
-        strict: false,
-        defer_loading: tool_definition.defer_loading.then_some(true),
-        parameters: tool_definition.input_schema,
-        output_schema: tool_definition.output_schema,
-    }
-}
-
 /// Builds the tool registry builder while collecting tool specs for later serialization.
 #[cfg(test)]
 pub(crate) fn build_specs(
@@ -2911,7 +2875,7 @@ pub(crate) fn build_specs_with_discoverable_tools(
         entries.sort_by(|a, b| a.0.cmp(&b.0));
 
         for (name, tool) in entries.into_iter() {
-            match mcp_tool_to_openai_tool(name.clone(), tool.clone()) {
+            match mcp_tool_to_responses_api_tool(name.clone(), &tool) {
                 Ok(converted_tool) => {
                     push_tool_spec(
                         &mut builder,
@@ -2930,7 +2894,7 @@ pub(crate) fn build_specs_with_discoverable_tools(
 
     if !dynamic_tools.is_empty() {
         for tool in dynamic_tools {
-            match dynamic_tool_to_openai_tool(tool) {
+            match dynamic_tool_to_responses_api_tool(tool) {
                 Ok(converted_tool) => {
                     push_tool_spec(
                         &mut builder,

codex-rs/core/src/tools/spec_tests.rs

@@ -8,11 +8,11 @@ use crate::tools::ToolRouter;
 use crate::tools::registry::ConfiguredToolSpec;
 use crate::tools::router::ToolRouterParams;
 use codex_app_server_protocol::AppInfo;
-use codex_protocol::dynamic_tools::DynamicToolSpec;
 use codex_protocol::openai_models::InputModality;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelsResponse;
 use codex_tools::AdditionalProperties;
+use codex_tools::mcp_tool_to_deferred_responses_api_tool;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use pretty_assertions::assert_eq;
 use std::path::PathBuf;
@@ -64,28 +64,6 @@ fn search_capable_model_info() -> ModelInfo {
     model_info
 }
 
-#[test]
-fn search_tool_deferred_tools_always_set_defer_loading_true() {
-    let tool = mcp_tool(
-        "lookup_order",
-        "Look up an order",
-        serde_json::json!({
-            "type": "object",
-            "properties": {
-                "order_id": {"type": "string"}
-            },
-            "required": ["order_id"],
-            "additionalProperties": false,
-        }),
-    );
-
-    let openai_tool =
-        mcp_tool_to_deferred_openai_tool("mcp__codex_apps__lookup_order".to_string(), tool)
-            .expect("convert deferred tool");
-
-    assert_eq!(openai_tool.defer_loading, Some(true));
-}
-
 #[test]
 fn deferred_responses_api_tool_serializes_with_defer_loading() {
     let tool = mcp_tool(
@@ -102,7 +80,7 @@ fn deferred_responses_api_tool_serializes_with_defer_loading() {
     );
 
     let serialized = serde_json::to_value(ToolSpec::Function(
-        mcp_tool_to_deferred_openai_tool("mcp__codex_apps__lookup_order".to_string(), tool)
+        mcp_tool_to_deferred_responses_api_tool("mcp__codex_apps__lookup_order".to_string(), &tool)
             .expect("convert deferred tool"),
     ))
     .expect("serialize deferred tool");
@@ -127,44 +105,6 @@ fn deferred_responses_api_tool_serializes_with_defer_loading() {
     );
 }
 
-#[test]
-fn dynamic_tool_preserves_defer_loading() {
-    let tool = DynamicToolSpec {
-        name: "lookup_order".to_string(),
-        description: "Look up an order".to_string(),
-        input_schema: serde_json::json!({
-            "type": "object",
-            "properties": {
-                "order_id": {"type": "string"}
-            },
-            "required": ["order_id"],
-            "additionalProperties": false,
-        }),
-        defer_loading: true,
-    };
-
-    let openai_tool = dynamic_tool_to_openai_tool(&tool).expect("convert dynamic tool");
-
-    assert_eq!(
-        openai_tool,
-        ResponsesApiTool {
-            name: "lookup_order".to_string(),
-            description: "Look up an order".to_string(),
-            strict: false,
-            defer_loading: Some(true),
-            parameters: JsonSchema::Object {
-                properties: BTreeMap::from([(
-                    "order_id".to_string(),
-                    JsonSchema::String { description: None },
-                )]),
-                required: Some(vec!["order_id".to_string()]),
-                additional_properties: Some(false.into()),
-            },
-            output_schema: None,
-        }
-    );
-}
-
 fn tool_name(tool: &ToolSpec) -> &str {
     match tool {
         ToolSpec::Function(ResponsesApiTool { name, .. }) => name,