Add spawn_agent model overrides (#14160)

- add `model` and `reasoning_effort` to the `spawn_agent` schema so the
values pass through
- validate requested models against `model.model` and only check that
the selected model supports the requested reasoning effort

---------

Co-authored-by: Codex <noreply@openai.com>

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

@@ -791,6 +791,24 @@ fn create_spawn_agent_tool(config: &ToolsConfig) -> ToolSpec {
                 ),
             },
         ),
+        (
+            "model".to_string(),
+            JsonSchema::String {
+                description: Some(
+                    "Optional model override for the new agent. Replaces the inherited model."
+                        .to_string(),
+                ),
+            },
+        ),
+        (
+            "reasoning_effort".to_string(),
+            JsonSchema::String {
+                description: Some(
+                    "Optional reasoning effort override for the new agent. Replaces the inherited reasoning effort."
+                        .to_string(),
+                ),
+            },
+        ),
     ]);
 
     ToolSpec::Function(ResponsesApiTool {