Make multi-agent v2 tool namespace configurable (#23147)

## Summary
- Add `features.multi_agent_v2.tool_namespace` with config/schema
validation for Responses-compatible namespace values.
- Thread the resolved namespace into `ToolsConfig` for normal turns and
review turns.
- Wrap MultiAgentV2 tool specs and registry names in the configured
namespace when namespace tools are supported, while falling back to the
plain tool names when they are not.

## Validation
- `just fmt`
- `just write-config-schema`
- `cargo test -p codex-features multi_agent_v2_feature_config --
--nocapture`
- `cargo test -p codex-core test_build_specs_multi_agent_v2 --
--nocapture`
- `cargo test -p codex-core multi_agent_v2_config -- --nocapture`
- `cargo test -p codex-core
multi_agent_v2_rejects_invalid_tool_namespace -- --nocapture`
- `cargo test -p codex-tools`
- `git diff --check`

codex-rs/features/src/feature_configs.rs

@@ -30,6 +30,9 @@ pub struct MultiAgentV2ConfigToml {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub subagent_usage_hint_text: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
+    #[schemars(length(min = 1, max = 64), regex(pattern = r"^[a-zA-Z0-9_-]+$"))]
+    pub tool_namespace: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub hide_spawn_agent_metadata: Option<bool>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub non_code_mode_only: Option<bool>,

codex-rs/features/src/tests.rs

@@ -528,6 +528,7 @@ usage_hint_enabled = false
 usage_hint_text = "Custom delegation guidance."
 root_agent_usage_hint_text = "Root guidance."
 subagent_usage_hint_text = "Subagent guidance."
+tool_namespace = "agents"
 hide_spawn_agent_metadata = true
 non_code_mode_only = true
 "#,
@@ -550,6 +551,7 @@ non_code_mode_only = true
             usage_hint_text: Some("Custom delegation guidance.".to_string()),
             root_agent_usage_hint_text: Some("Root guidance.".to_string()),
             subagent_usage_hint_text: Some("Subagent guidance.".to_string()),
+            tool_namespace: Some("agents".to_string()),
             hide_spawn_agent_metadata: Some(true),
             non_code_mode_only: Some(true),
         }))
@@ -588,6 +590,7 @@ usage_hint_enabled = false
             usage_hint_text: None,
             root_agent_usage_hint_text: None,
             subagent_usage_hint_text: None,
+            tool_namespace: None,
             hide_spawn_agent_metadata: None,
             non_code_mode_only: None,
         }))