Expose spawn agent types only when roles are configured (#33572)

## Why

The `agent_type` argument is only useful when agent roles are configured. Avoid
advertising an inapplicable override in the model-visible `spawn_agent` schema.

## What changed

- Include `agent_type` in the V1 and V2 spawn tools only when configured roles
  are available.
- Clarify that `agent_type` is an explicit override and document its interaction
  with context forking.
- Remove the unused `agents.support_agent_type` configuration field.

## Testing

- Add coverage for hiding `agent_type` without roles and exposing it when a role
  is configured.

GitOrigin-RevId: 32e0f123b15f317e9cdb71774029375bc073d9ad

codex-rs/core/src/config/config_tests.rs

@@ -7351,7 +7351,6 @@ async fn load_config_rejects_missing_agent_role_config_file() -> std::io::Result
             enabled: None,
             max_concurrent_threads_per_session: None,
             max_depth: None,
-            support_agent_type: None,
             default_subagent_model: None,
             default_subagent_reasoning_effort: None,
             job_max_runtime_seconds: None,
@@ -8279,7 +8278,6 @@ async fn load_config_resolves_agent_controls() -> std::io::Result<()> {
         agents: Some(AgentsToml {
             enabled: Some(false),
             max_depth: Some(2),
-            support_agent_type: Some(true),
             default_subagent_model: Some("gpt-5.6-terra".to_string()),
             default_subagent_reasoning_effort: Some(ReasoningEffort::High),
             interrupt_message: Some(false),
@@ -8299,7 +8297,6 @@ async fn load_config_resolves_agent_controls() -> std::io::Result<()> {
         (
             config.agents_enabled,
             config.agent_max_depth,
-            config.agent_support_agent_type,
             config.agent_default_subagent_model.as_deref(),
             config.agent_default_subagent_reasoning_effort,
             config.agent_interrupt_message_enabled,
@@ -8307,7 +8304,6 @@ async fn load_config_resolves_agent_controls() -> std::io::Result<()> {
         (
             false,
             2,
-            Some(true),
             Some("gpt-5.6-terra"),
             Some(ReasoningEffort::High),
             false,
@@ -8346,7 +8342,6 @@ async fn load_config_normalizes_agent_role_nickname_candidates() -> std::io::Res
             enabled: None,
             max_concurrent_threads_per_session: None,
             max_depth: None,
-            support_agent_type: None,
             default_subagent_model: None,
             default_subagent_reasoning_effort: None,
             job_max_runtime_seconds: None,
@@ -8393,7 +8388,6 @@ async fn load_config_rejects_empty_agent_role_nickname_candidates() -> std::io::
             enabled: None,
             max_concurrent_threads_per_session: None,
             max_depth: None,
-            support_agent_type: None,
             default_subagent_model: None,
             default_subagent_reasoning_effort: None,
             job_max_runtime_seconds: None,
@@ -8434,7 +8428,6 @@ async fn load_config_rejects_duplicate_agent_role_nickname_candidates() -> std::
             enabled: None,
             max_concurrent_threads_per_session: None,
             max_depth: None,
-            support_agent_type: None,
             default_subagent_model: None,
             default_subagent_reasoning_effort: None,
             job_max_runtime_seconds: None,
@@ -8475,7 +8468,6 @@ async fn load_config_rejects_unsafe_agent_role_nickname_candidates() -> std::io:
             enabled: None,
             max_concurrent_threads_per_session: None,
             max_depth: None,
-            support_agent_type: None,
             default_subagent_model: None,
             default_subagent_reasoning_effort: None,
             job_max_runtime_seconds: None,

codex-rs/core/src/config/mod.rs

@@ -863,9 +863,6 @@ pub struct Config {
     /// User-configured maximum number of spawned agent threads per session.
     pub agent_max_threads: Option<usize>,
 
-    /// Reserved setting for whether the spawn tool supports agent types.
-    pub agent_support_agent_type: Option<bool>,
-
     /// Reserved default model for spawned subagents.
     pub agent_default_subagent_model: Option<String>,
 
@@ -3606,10 +3603,6 @@ impl Config {
             .as_ref()
             .and_then(|agents| agents.max_depth)
             .unwrap_or(DEFAULT_AGENT_MAX_DEPTH);
-        let agent_support_agent_type = cfg
-            .agents
-            .as_ref()
-            .and_then(|agents| agents.support_agent_type);
         let agent_default_subagent_model = cfg
             .agents
             .as_ref()
@@ -3970,7 +3963,6 @@ impl Config {
             tool_output_token_limit: cfg.tool_output_token_limit,
             agents_enabled,
             agent_max_threads,
-            agent_support_agent_type,
             agent_default_subagent_model,
             agent_default_subagent_reasoning_effort,
             agent_max_depth,