[tool search] support namespaced deferred dynamic tools (#18413)

Deferred dynamic tools need to round-trip a namespace so a tool returned
by `tool_search` can be called through the same registry key that core
uses for dispatch.

This change adds namespace support for dynamic tool specs/calls,
persists it through app-server thread state, and routes dynamic tool
calls by full `ToolName` while still sending the app the leaf tool name.
Deferred dynamic tools must provide a namespace; non-deferred dynamic
tools may remain top-level.

It also introduces `LoadableToolSpec` as the shared
function-or-namespace Responses shape used by both `tool_search` output
and dynamic tool registration, so dynamic tools use the same wrapping
logic in both paths.

Validation:
- `cargo test -p codex-tools`
- `cargo test -p codex-core tool_search`

---------

Co-authored-by: Sayan Sisodiya <sayan@openai.com>

codex-rs/tools/src/lib.rs

@@ -44,6 +44,7 @@ pub use apply_patch_tool::ApplyPatchToolArgs;
 pub use apply_patch_tool::create_apply_patch_freeform_tool;
 pub use apply_patch_tool::create_apply_patch_json_tool;
 pub use code_mode::augment_tool_spec_for_code_mode;
+pub use code_mode::code_mode_name_for_tool_name;
 pub use code_mode::collect_code_mode_exec_prompt_tool_definitions;
 pub use code_mode::collect_code_mode_tool_definitions;
 pub use code_mode::create_code_mode_tool;
@@ -82,11 +83,13 @@ pub use request_user_input_tool::request_user_input_tool_description;
 pub use request_user_input_tool::request_user_input_unavailable_message;
 pub use responses_api::FreeformTool;
 pub use responses_api::FreeformToolFormat;
+pub use responses_api::LoadableToolSpec;
 pub use responses_api::ResponsesApiNamespace;
 pub use responses_api::ResponsesApiNamespaceTool;
 pub use responses_api::ResponsesApiTool;
-pub use responses_api::ToolSearchOutputTool;
+pub use responses_api::coalesce_loadable_tool_specs;
 pub(crate) use responses_api::default_namespace_description;
+pub use responses_api::dynamic_tool_to_loadable_tool_spec;
 pub use responses_api::dynamic_tool_to_responses_api_tool;
 pub use responses_api::mcp_tool_to_deferred_responses_api_tool;
 pub use responses_api::mcp_tool_to_responses_api_tool;
@@ -114,7 +117,7 @@ pub use tool_discovery::collect_tool_suggest_entries;
 pub use tool_discovery::create_tool_search_tool;
 pub use tool_discovery::create_tool_suggest_tool;
 pub use tool_discovery::filter_tool_suggest_discoverable_tools_for_client;
-pub use tool_discovery::tool_search_result_source_to_output_tool;
+pub use tool_discovery::tool_search_result_source_to_loadable_tool_spec;
 pub use tool_registry_plan::build_tool_registry_plan;
 pub use tool_registry_plan_types::ToolHandlerKind;
 pub use tool_registry_plan_types::ToolHandlerSpec;