Fix full-history model override guidance

Author: diogovalada

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

@@ -11668,6 +11668,7 @@ fn multi_agent_v2_exposes_model_overrides_by_default() {
             .expect("model-override guidance should extend the base usage hint");
         for required_fragment in [
             "Full-history forks",
+            "accept explicit `model` and `reasoning_effort` overrides",
             "`fork_turns`",
             "`model`",
             "`reasoning_effort`",
@@ -11677,6 +11678,10 @@ fn multi_agent_v2_exposes_model_overrides_by_default() {
                 "model-override guidance should contain {required_fragment}"
             );
         }
+        assert!(
+            !model_override_guidance.contains("do not accept overrides"),
+            "model-override guidance should not retain the obsolete prohibition"
+        );
     }
 }
 

codex-rs/core/src/session/multi_agents.rs

@@ -47,7 +47,7 @@ Payload:
 ```
 You may also see them addressed as to=/root/..., which indicates your identity is /root/...
 "#;
-const DEFAULT_MULTI_AGENT_V2_MODEL_OVERRIDE_USAGE_HINT_TEXT: &str = "Full-history forks (`fork_turns` omitted or `\"all\"`) inherit the parent model and reasoning effort and do not accept overrides. Only set `model` or `reasoning_effort` when explicitly requested by the user, applicable `AGENTS.md` instructions, or skill instructions; when doing so, set `fork_turns` to `\"none\"` or a positive integer string.";
+const DEFAULT_MULTI_AGENT_V2_MODEL_OVERRIDE_USAGE_HINT_TEXT: &str = "Full-history forks (`fork_turns` omitted or `\"all\"`) accept explicit `model` and `reasoning_effort` overrides. Only set these overrides when explicitly requested by the user, applicable `AGENTS.md` instructions, or skill instructions.";
 const DEFAULT_MULTI_AGENT_V2_WAIT_AGENT_USAGE_HINT_TEXT: &str =
     "When calling `wait_agent`, prefer longer waits (minutes) to avoid busy polling.";
 const DEFAULT_MULTI_AGENT_V2_SHARED_USAGE_HINT_TEXT: &str = r#"Note that collaboration tools cannot be called from inside `functions.exec`. Call `spawn_agent`, `send_message`, `followup_task`, `wait_agent`, `interrupt_agent`, and `list_agents` only as direct tool calls using the recipient shown in their tool definitions, such as `to=functions.collaboration.spawn_agent`, since they are intentionally absent from the `functions.exec` `tools.*` namespace. Available tools in `functions.exec` are explicitly described with a `tools` namespace in the developer message.

codex-rs/core/src/tools/handlers/multi_agents_spec.rs

@@ -14,10 +14,12 @@ use std::collections::BTreeMap;
 pub const MULTI_AGENT_V1_NAMESPACE: &str = "multi_agent_v1";
 const MULTI_AGENT_V1_NAMESPACE_DESCRIPTION: &str = "Tools for spawning and managing sub-agents.";
 
-const SPAWN_AGENT_INHERITED_MODEL_GUIDANCE: &str = "Spawned agents inherit your current model by default. Omit `model` to use that preferred default; set `model` only when an explicit override is needed.";
+const SPAWN_AGENT_INHERITED_MODEL_GUIDANCE: &str = "Spawned agents normally inherit your current model unless configured subagent defaults or a selected role apply. Omit `model` to use the resulting default; set `model` only when an explicit override is needed.";
 const SPAWN_AGENT_TYPE_OVERRIDE_DESCRIPTION_V1: &str = "Agent type override for the new agent. Omit to inherit the parent agent type with a full-history fork; otherwise, `default` is used.";
 const SPAWN_AGENT_MODEL_OVERRIDE_DESCRIPTION: &str =
     "Model override for the new agent. Omit unless an explicit override is needed.";
+const SPAWN_AGENT_REASONING_EFFORT_OVERRIDE_DESCRIPTION: &str =
+    "Reasoning effort override for the new agent. Omit unless an explicit override is needed.";
 const SPAWN_AGENT_SERVICE_TIER_OVERRIDE_DESCRIPTION: &str =
     "Service tier override for the new agent. Omit unless explicitly requested.";
 const MAX_REASONING_EFFORT_CHARS_IN_SPAWN_AGENT_DESCRIPTION: usize = 64;
@@ -615,8 +617,7 @@ fn spawn_agent_common_properties_v1(agent_type_description: &str) -> BTreeMap<St
         (
             "reasoning_effort".to_string(),
             JsonSchema::string(Some(
-                "Reasoning effort override for the new agent. Omit to inherit the parent effort."
-                    .to_string(),
+                SPAWN_AGENT_REASONING_EFFORT_OVERRIDE_DESCRIPTION.to_string(),
             )),
         ),
         (
@@ -659,8 +660,7 @@ fn spawn_agent_common_properties_v2(agent_type_description: &str) -> BTreeMap<St
         (
             "reasoning_effort".to_string(),
             JsonSchema::string(Some(
-                "Reasoning effort override for the new agent. Omit to inherit the parent effort."
-                    .to_string(),
+                SPAWN_AGENT_REASONING_EFFORT_OVERRIDE_DESCRIPTION.to_string(),
             )),
         ),
         (

codex-rs/core/src/tools/handlers/multi_agents_spec_tests.rs

@@ -113,7 +113,7 @@ fn spawn_agent_tool_v2_requires_task_name_and_lists_visible_models() {
         properties
             .get("reasoning_effort")
             .and_then(|schema| schema.description.as_deref()),
-        Some("Reasoning effort override for the new agent. Omit to inherit the parent effort.")
+        Some(SPAWN_AGENT_REASONING_EFFORT_OVERRIDE_DESCRIPTION)
     );
     assert_eq!(
         properties