[codex-analytics] guardian review TTFT plumbing and emission (#17696)

## Why

Guardian analytics includes time-to-first-token, but the Guardian
reviewer runs as a normal Codex session and `TurnCompleteEvent` did not
expose TTFT. The timing needs to flow through the standard
turn-completion protocol so Guardian review analytics can consume the
same value as the rest of the session machinery.

## What changed

Adds optional `time_to_first_token_ms` to `TurnCompleteEvent` and
populates it from `TurnTiming`. The value is carried through app-server
thread history, rollout reconstruction, TUI/app-server adapters, and
Guardian review session handling.

Guardian review analytics now captures TTFT from the reviewer
turn-complete event when available. Existing tests and fixtures are
updated to set the new optional field to `None` where TTFT is not
relevant.

## Verification

- `cargo clippy -p codex-tui --tests -- -D warnings`
- `cargo clippy -p codex-core --lib --tests -- -D warnings`

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/17696).
* __->__ #17696
* #17695
* #17693
* #18278
* #18953

codex-rs/tui/src/chatwidget/tests/exec_flow.rs

@@ -654,6 +654,7 @@ async fn unified_exec_wait_after_final_agent_message_snapshot() {
             last_agent_message: Some("Final response.".into()),
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -699,6 +700,7 @@ async fn unified_exec_wait_before_streamed_agent_message_snapshot() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -766,6 +768,7 @@ async fn unified_exec_waiting_multiple_empty_snapshots() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -846,6 +849,7 @@ async fn unified_exec_non_empty_then_empty_snapshots() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -1072,6 +1076,7 @@ async fn user_message_during_user_shell_command_is_queued_not_steered() {
             last_agent_message: Some("done".to_string()),
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -1411,6 +1416,7 @@ async fn turn_complete_keeps_unified_exec_processes() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 

codex-rs/tui/src/chatwidget/tests/plan_mode.rs

@@ -686,6 +686,7 @@ async fn plan_implementation_popup_skips_replayed_turn_complete() {
         last_agent_message: Some("Plan details".to_string()),
         completed_at: None,
         duration_ms: None,
+        time_to_first_token_ms: None,
     })]);
 
     let popup = render_bottom_popup(&chat, /*width*/ 80);
@@ -712,6 +713,7 @@ async fn plan_implementation_popup_shows_once_when_replay_precedes_live_turn_com
         last_agent_message: Some("Plan details".to_string()),
         completed_at: None,
         duration_ms: None,
+        time_to_first_token_ms: None,
     })]);
     let replay_popup = render_bottom_popup(&chat, /*width*/ 80);
     assert!(
@@ -726,6 +728,7 @@ async fn plan_implementation_popup_shows_once_when_replay_precedes_live_turn_com
             last_agent_message: Some("Plan details".to_string()),
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -749,6 +752,7 @@ async fn plan_implementation_popup_shows_once_when_replay_precedes_live_turn_com
             last_agent_message: Some("Plan details".to_string()),
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
     let duplicate_popup = render_bottom_popup(&chat, /*width*/ 80);

codex-rs/tui/src/chatwidget/tests/review_mode.rs

@@ -314,6 +314,7 @@ async fn steer_rejection_queues_review_follow_up_before_existing_queued_messages
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -335,6 +336,7 @@ async fn steer_rejection_queues_review_follow_up_before_existing_queued_messages
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 

codex-rs/tui/src/chatwidget/tests/slash_commands.rs

@@ -807,6 +807,7 @@ async fn slash_copy_state_tracks_turn_complete_final_reply() {
             last_agent_message: Some("Final reply **markdown**".to_string()),
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -839,6 +840,7 @@ async fn slash_copy_state_tracks_plan_item_completion() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -925,6 +927,7 @@ async fn slash_copy_state_is_preserved_during_running_task() {
             last_agent_message: Some("Previous completed reply".to_string()),
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
     chat.on_task_started();
@@ -955,6 +958,7 @@ async fn slash_copy_tracks_replayed_legacy_agent_message_when_turn_complete_omit
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
     let _ = drain_insert_history(&mut rx);
@@ -992,6 +996,7 @@ async fn slash_copy_uses_agent_message_item_when_turn_complete_omits_final_text(
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
     let _ = drain_insert_history(&mut rx);

codex-rs/tui/src/chatwidget/tests/status_and_layout.rs

@@ -1315,6 +1315,7 @@ async fn status_line_branch_refreshes_after_turn_complete() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -1665,6 +1666,7 @@ async fn multiple_agent_messages_in_single_turn_emit_multiple_headers() {
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
 
@@ -2610,6 +2612,7 @@ printf 'fenced within fenced\n'
             last_agent_message: None,
             completed_at: None,
             duration_ms: None,
+            time_to_first_token_ms: None,
         }),
     });
     for lines in drain_insert_history(&mut rx) {