Record saved multi-agent opt-outs in session telemetry (#59478)

## Why

Saved `features.multi_agent = false` settings can be overridden by a higher-precedence session setting. Session telemetry should retain visibility into those saved opt-outs.

## What changed

Add `config.legacy_multi_agent_disabled_sources` to `codex.conversation_starts`, reporting opt-outs from user configuration, project configuration, and managed requirements. Emit comma-separated source labels, or `none` when no opt-outs are found.

## Testing

Add a regression test confirming that a user opt-out is still reported when a CLI override enables multi-agent support for the session.

GitOrigin-RevId: 488bd317d67e9ee87c5903ae51f466e0a63c05eb

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

@@ -10133,6 +10133,27 @@ job_max_runtime_seconds = 900
     );
 }
 
+#[tokio::test]
+async fn legacy_multi_agent_opt_out_survives_a_session_override() -> std::io::Result<()> {
+    let home = TempDir::new()?;
+    std::fs::write(
+        home.path().join(CONFIG_TOML_FILE),
+        "[features]\nmulti_agent = false\n",
+    )?;
+    let config = ConfigBuilder::without_managed_config_for_tests()
+        .codex_home(home.path().to_path_buf())
+        .fallback_cwd(Some(home.path().to_path_buf()))
+        .cli_overrides(vec![("features.multi_agent".to_string(), true.into())])
+        .build()
+        .await?;
+    assert!(config.features.enabled(Feature::Collab));
+    assert_eq!(
+        legacy_multi_agent_disabled_sources(&config.config_layer_stack),
+        ["user"]
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn load_config_resolves_agent_controls() -> std::io::Result<()> {
     let codex_home = TempDir::new()?;

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

@@ -1,6 +1,8 @@
 //! Metrics derived from loaded configuration at session start.
 
 use super::Config;
+use codex_config::ConfigLayerSource;
+use codex_config::ConfigLayerStack;
 use codex_features::FEATURES;
 use codex_features::Stage;
 use codex_otel::SessionTelemetry;
@@ -24,3 +26,38 @@ pub(crate) fn emit_session_start_metrics(config: &Config, telemetry: &SessionTel
     #[cfg(windows)]
     crate::windows_system_config::emit_namespace_squatting_probe();
 }
+
+/// Report saved opt-outs even when a higher-precedence session setting overrides them.
+pub(crate) fn legacy_multi_agent_disabled_sources(layers: &ConfigLayerStack) -> Vec<&'static str> {
+    let mut user = None;
+    let mut project = None;
+    for layer in layers.layers_low_to_high() {
+        let setting = match layer.name {
+            ConfigLayerSource::User { .. } => &mut user,
+            ConfigLayerSource::Project { .. } => &mut project,
+            _ => continue,
+        };
+        if let Some(value) = layer
+            .config
+            .get("features")
+            .and_then(|features| features.get("multi_agent"))
+            .and_then(toml::Value::as_bool)
+        {
+            *setting = Some(value);
+        }
+    }
+    let managed = layers
+        .requirements()
+        .feature_requirements
+        .as_ref()
+        .and_then(|requirements| requirements.value.entries.get("multi_agent"))
+        .copied();
+    [
+        ("user", user),
+        ("project", project),
+        ("managed_requirement", managed),
+    ]
+    .into_iter()
+    .filter_map(|(source, value)| (value == Some(false)).then_some(source))
+    .collect()
+}

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

@@ -201,6 +201,7 @@ use codex_sandboxing::compatibility_sandbox_policy_for_permission_profile;
 pub use codex_sandboxing::system_bwrap_warning;
 pub use managed_features::ManagedFeatures;
 pub(crate) use metrics::emit_session_start_metrics;
+pub(crate) use metrics::legacy_multi_agent_disabled_sources;
 pub use network_config::EnvironmentNetworkConfigError;
 pub use network_config::NetworkConfigInputs;
 pub use network_config::PreparedNetworkConfig;

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

@@ -1512,6 +1512,7 @@ impl Session {
                     .permissions
                     .legacy_sandbox_policy(session_configuration.cwd().as_path()),
                 mcp_server_names.iter().map(String::as_str).collect(),
+                &crate::config::legacy_multi_agent_disabled_sources(&config.config_layer_stack),
             );
 
             let default_shell = session_configuration

codex-rs/otel/src/events/session_telemetry.rs

@@ -696,11 +696,17 @@ impl SessionTelemetry {
         approval_policy: AskForApproval,
         sandbox_policy: SandboxPolicy,
         mcp_servers: Vec<&str>,
+        legacy_multi_agent_disabled_sources: &[&str],
     ) {
         log_and_trace_event!(
             self,
             common: {
                 event.name = "codex.conversation_starts",
+                config.legacy_multi_agent_disabled_sources = if legacy_multi_agent_disabled_sources.is_empty() {
+                    "none".to_string()
+                } else {
+                    legacy_multi_agent_disabled_sources.join(",")
+                },
                 provider_name = %provider_name,
                 auth.env_openai_api_key_present = self.metadata.auth_env.openai_api_key_env_present,
                 auth.env_codex_api_key_present = self.metadata.auth_env.codex_api_key_env_present,

codex-rs/otel/tests/suite/otel_export_routing_policy.rs

@@ -883,6 +883,7 @@ fn otel_export_routing_policy_routes_api_request_auth_observability() {
             AskForApproval::Never,
             SandboxPolicy::DangerFullAccess,
             Vec::new(),
+            /*legacy_multi_agent_disabled_sources*/ &[],
         );
         let agent_identity_telemetry = AgentIdentityTelemetry {
             agent_id: "agent-runtime-otel".to_string(),