revert legacy notify deprecation (#21152)

# Why

Revert #20524 for now because the computer use plugin has not migrated
off legacy `notify` yet. Keeping the deprecation in place today would
show users a warning before the plugin path is ready to move, so this
rolls the change back until that migration is complete.

# What

- revert the legacy `notify` deprecation change from #20524
- restore the prior `notify` behavior and remove the temporary
deprecation metrics/docs from that change

Once the computer use plugin has migrated, we can land the same
deprecation again.

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

@@ -480,7 +480,7 @@ pub struct Config {
     /// - `Some("...")`: use the provided attribution text verbatim
     pub commit_attribution: Option<String>,
 
-    /// Deprecated optional external notifier command. When set, Codex will spawn this
+    /// Optional external notifier command. When set, Codex will spawn this
     /// program after each completed *turn* (i.e. when the agent finishes
     /// processing a user submission). The value must be the full command
     /// broken into argv tokens **without** the trailing JSON argument - Codex
@@ -499,7 +499,7 @@ pub struct Config {
     /// notify-send Codex '{"type":"agent-turn-complete","turn-id":"12345"}'
     /// ```
     ///
-    /// If unset the feature is disabled. Use lifecycle hooks for new automation.
+    /// If unset the feature is disabled.
     pub notify: Option<Vec<String>>,
 
     /// TUI notification settings, including enabled events, delivery method, and focus condition.

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

@@ -1,6 +1,5 @@
 use super::*;
 use crate::goals::GoalRuntimeState;
-use codex_otel::LEGACY_NOTIFY_CONFIGURED_METRIC;
 use codex_protocol::permissions::FileSystemPath;
 use codex_protocol::permissions::FileSystemSpecialPath;
 use codex_protocol::protocol::TurnEnvironmentSelection;
@@ -573,24 +572,6 @@ impl Session {
                     }),
                 });
             }
-            let legacy_notify_configured = config
-                .notify
-                .as_ref()
-                .is_some_and(|argv| !argv.is_empty() && !argv[0].is_empty());
-            if legacy_notify_configured {
-                post_session_configured_events.push(Event {
-                    id: INITIAL_SUBMIT_ID.to_owned(),
-                    msg: EventMsg::DeprecationNotice(DeprecationNoticeEvent {
-                        summary:
-                            "`notify` is deprecated and will be removed in a future release."
-                                .to_string(),
-                        details: Some(
-                            "Switch to a `Stop` hook for end-of-turn automation. See https://developers.openai.com/codex/hooks."
-                                .to_string(),
-                        ),
-                    }),
-                });
-            }
             for message in &config.startup_warnings {
                 post_session_configured_events.push(Event {
                     id: "".to_owned(),
@@ -648,9 +629,6 @@ impl Session {
             if let Some(service_name) = session_configuration.metrics_service_name.as_deref() {
                 session_telemetry = session_telemetry.with_metrics_service_name(service_name);
             }
-            if legacy_notify_configured {
-                session_telemetry.counter(LEGACY_NOTIFY_CONFIGURED_METRIC, /*inc*/ 1, &[]);
-            }
             let network_proxy_audit_metadata = NetworkProxyAuditMetadata {
                 conversation_id: Some(conversation_id.to_string()),
                 app_version: Some(env!("CARGO_PKG_VERSION").to_string()),

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

@@ -72,7 +72,6 @@ use codex_hooks::HookEvent;
 use codex_hooks::HookEventAfterAgent;
 use codex_hooks::HookPayload;
 use codex_hooks::HookResult;
-use codex_otel::LEGACY_NOTIFY_RUN_METRIC;
 use codex_protocol::config_types::ModeKind;
 use codex_protocol::error::CodexErr;
 use codex_protocol::error::Result as CodexResult;
@@ -580,13 +579,6 @@ pub(crate) async fn run_turn(
                             },
                         })
                         .await;
-                    if !hook_outcomes.is_empty() {
-                        turn_context.session_telemetry.counter(
-                            LEGACY_NOTIFY_RUN_METRIC,
-                            /*inc*/ 1,
-                            &[],
-                        );
-                    }
 
                     let mut abort_message = None;
                     for hook_outcome in hook_outcomes {