codex-tools: extract utility tool specs (#16154)

## Why

The previous `codex-tools` migration steps moved the shared schema
models, local-host specs, collaboration specs, and related adapters out
of `codex-core`, but `core/src/tools/spec.rs` still contained a grab bag
of pure utility tool builders. Those specs do not need session state or
handler logic; they only describe wire shapes for tools that
`codex-core` already knows how to execute.

Moving that remaining low-coupling layer into `codex-tools` keeps the
migration moving in meaningful chunks and trims another large block of
passive tool-spec construction out of `codex-core` without touching the
runtime-coupled handlers.

## What changed

- extended `codex-tools` to own the pure spec builders for:
  - code-mode `exec` / `wait`
  - `js_repl` / `js_repl_reset`
- MCP resource tools `list_mcp_resources`,
`list_mcp_resource_templates`, and `read_mcp_resource`
  - utility tools `list_dir` and `test_sync_tool`
- split those builders across small module files with sibling
`*_tests.rs` coverage, keeping `src/lib.rs` exports-only
- rewired `core/src/tools/spec.rs` to call the extracted builders and
deleted the duplicated core-local implementations
- moved the direct JS REPL grammar seam test out of
`core/src/tools/spec_tests.rs` so it now lives with the extracted
implementation in `codex-tools`
- updated `codex-rs/tools/README.md` so the documented crate boundary
matches the new utility-spec surface

## Test plan

- `CARGO_TARGET_DIR=/tmp/codex-tools-utility-specs cargo test -p
codex-tools`
- `CARGO_TARGET_DIR=/tmp/codex-core-utility-specs cargo test -p
codex-core --lib tools::spec::`
- `just fix -p codex-tools -p codex-core`
- `just argument-comment-lint`

## References

- #15923
- #15928
- #15944
- #15953
- #16031
- #16047
- #16129
- #16132
- #16138
- #16141

codex-rs/tools/src/lib.rs

@@ -5,13 +5,16 @@ mod agent_job_tool;
 mod agent_tool;
 mod code_mode;
 mod dynamic_tool;
+mod js_repl_tool;
 mod json_schema;
 mod local_tool;
+mod mcp_resource_tool;
 mod mcp_tool;
 mod request_user_input_tool;
 mod responses_api;
 mod tool_definition;
 mod tool_spec;
+mod utility_tool;
 mod view_image;
 
 pub use agent_job_tool::create_report_agent_job_result_tool;
@@ -30,8 +33,12 @@ pub use agent_tool::create_spawn_agent_tool_v2;
 pub use agent_tool::create_wait_agent_tool_v1;
 pub use agent_tool::create_wait_agent_tool_v2;
 pub use code_mode::augment_tool_spec_for_code_mode;
+pub use code_mode::create_code_mode_tool;
+pub use code_mode::create_wait_tool;
 pub use code_mode::tool_spec_to_code_mode_tool_definition;
 pub use dynamic_tool::parse_dynamic_tool;
+pub use js_repl_tool::create_js_repl_reset_tool;
+pub use js_repl_tool::create_js_repl_tool;
 pub use json_schema::AdditionalProperties;
 pub use json_schema::JsonSchema;
 pub use json_schema::parse_tool_input_schema;
@@ -42,6 +49,9 @@ pub use local_tool::create_request_permissions_tool;
 pub use local_tool::create_shell_command_tool;
 pub use local_tool::create_shell_tool;
 pub use local_tool::create_write_stdin_tool;
+pub use mcp_resource_tool::create_list_mcp_resource_templates_tool;
+pub use mcp_resource_tool::create_list_mcp_resources_tool;
+pub use mcp_resource_tool::create_read_mcp_resource_tool;
 pub use mcp_tool::mcp_call_tool_result_output_schema;
 pub use mcp_tool::parse_mcp_tool;
 pub use request_user_input_tool::create_request_user_input_tool;
@@ -61,5 +71,7 @@ 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 utility_tool::create_list_dir_tool;
+pub use utility_tool::create_test_sync_tool;
 pub use view_image::ViewImageToolOptions;
 pub use view_image::create_view_image_tool;