Log TUI app event variants without their payloads (#39709)

## Why

The TUI session logger is meant to record only the variant for unhandled app
events. Parsing `Debug` output removed tuple payloads but retained fields from
struct variants.

## What changed

Derive `IntoStaticStr` for `AppEvent` and use that conversion when recording
fallback `app_event` entries, so the `variant` field consistently contains only
the enum variant name.

GitOrigin-RevId: 5b539f414269c6b001e69cf9496db5b49aceb759

codex-rs/tui/src/app_event.rs

@@ -40,6 +40,7 @@ use codex_protocol::ThreadId;
 use codex_protocol::openai_models::ModelPreset;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_approval_presets::ApprovalPreset;
+use strum_macros::IntoStaticStr;
 use uuid::Uuid;
 
 use crate::app_command::AppCommand;
@@ -193,7 +194,7 @@ pub(crate) enum TranscriptExportDestination {
 }
 
 #[allow(clippy::large_enum_variant)]
-#[derive(Debug)]
+#[derive(Debug, IntoStaticStr)]
 pub(crate) enum AppEvent {
     /// Open the daemon-wide overview of loaded root sessions.
     OpenAgentsOverview,

codex-rs/tui/src/session_log.rs

@@ -199,11 +199,12 @@ pub(crate) fn log_inbound_app_event(event: &AppEvent) {
         }
         // Noise or control flow – record variant only
         other => {
+            let variant: &'static str = other.into();
             let value = json!({
                 "ts": now_ts(),
                 "dir": "to_tui",
                 "kind": "app_event",
-                "variant": format!("{other:?}").split('(').next().unwrap_or("app_event"),
+                "variant": variant,
             });
             LOGGER.write_json_line(value);
         }