codex-tools: extract local host tool specs (#16138)

## Why

`core/src/tools/spec.rs` still bundled a set of pure local-host tool
builders with the orchestration that actually decides when those tools
are exposed and which handlers back them. That made `codex-core`
responsible for JSON/tool-shape construction that does not depend on
session state, and it kept the `codex-tools` migration from taking a
meaningfully larger bite out of `spec.rs`.

This PR moves that reusable spec-building layer into `codex-tools` while
leaving feature gating, handler registration, and runtime-coupled
descriptions in `codex-core`.

## What changed

- added `codex-rs/tools/src/local_tool.rs` for the pure builders for
`exec_command`, `write_stdin`, `shell`, `shell_command`, and
`request_permissions`
- added `codex-rs/tools/src/view_image.rs` for the `view_image` tool
spec and output schema so the extracted modules stay right-sized
- rewired `codex-rs/core/src/tools/spec.rs` to call those extracted
builders instead of constructing these specs inline
- kept the `request_permissions` description source in `codex-core`,
with `codex-tools` taking the description as input so the crate boundary
does not grow a dependency on handler/runtime code
- moved the direct constructor coverage for this slice from
`codex-rs/core/src/tools/spec_tests.rs` into
`codex-rs/tools/src/local_tool_tests.rs` and
`codex-rs/tools/src/view_image_tests.rs`
- updated `codex-rs/tools/README.md` to reflect that `codex-tools` now
owns this local-host spec layer

## Test plan

- `CARGO_TARGET_DIR=/tmp/codex-tools-local-host cargo test -p
codex-tools`
- `CARGO_TARGET_DIR=/tmp/codex-core-local-tools cargo test -p codex-core
--lib tools::spec::`
- `just argument-comment-lint`

## References

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

codex-rs/tools/src/lib.rs

@@ -4,10 +4,12 @@
 mod code_mode;
 mod dynamic_tool;
 mod json_schema;
+mod local_tool;
 mod mcp_tool;
 mod responses_api;
 mod tool_definition;
 mod tool_spec;
+mod view_image;
 
 pub use code_mode::augment_tool_spec_for_code_mode;
 pub use code_mode::tool_spec_to_code_mode_tool_definition;
@@ -15,6 +17,13 @@ pub use dynamic_tool::parse_dynamic_tool;
 pub use json_schema::AdditionalProperties;
 pub use json_schema::JsonSchema;
 pub use json_schema::parse_tool_input_schema;
+pub use local_tool::CommandToolOptions;
+pub use local_tool::ShellToolOptions;
+pub use local_tool::create_exec_command_tool;
+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_tool::mcp_call_tool_result_output_schema;
 pub use mcp_tool::parse_mcp_tool;
 pub use responses_api::FreeformTool;
@@ -33,3 +42,5 @@ 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 view_image::ViewImageToolOptions;
+pub use view_image::create_view_image_tool;