Add structured asynchronous user input requests (#42178)

## What changed

- Replace `send_user_message_async` with `request_user_input_async`, accepting one or more questions with optional suggested answers while allowing the turn to continue.
- Attach structured question metadata to asynchronous agent messages while retaining readable fallback text, and preserve it through app-server events, thread history, and generated schemas.
- Continue enabling the new tool for model catalogs that advertise either the old or new tool name.

## Testing

- Cover tool registration, question validation, emitted items, continued turn execution, history preservation, and backwards-compatible deserialization.

GitOrigin-RevId: ffc49aebde2e854c3c50a122aa52805fec3fc6b3

codex-rs/app-server/tests/suite/v2/external_agent_config.rs

@@ -2045,6 +2045,7 @@ async fn external_agent_config_import_creates_session_rollouts() -> Result<()> {
             phase: None,
             memory_citation: None,
             delivery: None,
+            questions: None,
         })
     );
 

codex-rs/app-server/tests/suite/v2/history_notes_extension.rs

@@ -260,8 +260,8 @@ async fn history_notes_and_async_message_emit_control_tool_analytics() -> Result
         ),
         (
             "functions",
-            "send_user_message_async",
-            json!({"message": "PRIVATE_MESSAGE"}),
+            "request_user_input_async",
+            json!({"questions": [{"title": "PRIVATE_MESSAGE"}]}),
         ),
         (
             "notes",
@@ -270,8 +270,8 @@ async fn history_notes_and_async_message_emit_control_tool_analytics() -> Result
         ),
         (
             "functions",
-            "send_user_message_async",
-            json!({"message": " "}),
+            "request_user_input_async",
+            json!({"questions": [{"title": " "}]}),
         ),
     ];
     let server = responses::start_mock_server().await;

codex-rs/app-server/tests/suite/v2/thread_read.rs

@@ -584,6 +584,7 @@ async fn thread_search_occurrences_reads_paginated_projection() -> Result<()> {
                         phase: Some(MessagePhase::Commentary),
                         memory_citation: None,
                         delivery: None,
+                        questions: None,
                     }),
                 ),
                 paginated_completed_item(
@@ -597,6 +598,7 @@ async fn thread_search_occurrences_reads_paginated_projection() -> Result<()> {
                         phase: Some(MessagePhase::FinalAnswer),
                         memory_citation: None,
                         delivery: None,
+                        questions: None,
                     }),
                 ),
                 paginated_turn_completed("turn-1"),
@@ -1627,6 +1629,7 @@ async fn paginated_history_lists_and_legacy_reads_use_projected_turns_and_items(
                         phase: None,
                         memory_citation: None,
                         delivery: None,
+                        questions: None,
                     }),
                 ),
                 paginated_completed_item(
@@ -1679,6 +1682,7 @@ async fn paginated_history_lists_and_legacy_reads_use_projected_turns_and_items(
                 phase: None,
                 memory_citation: None,
                 delivery: None,
+                questions: None,
             },
         ],
         items_view: TurnItemsView::Full,
@@ -1865,6 +1869,7 @@ async fn paginated_history_lists_and_legacy_reads_use_projected_turns_and_items(
                     phase: None,
                     memory_citation: None,
                     delivery: None,
+                    questions: None,
                 },
             ],
             items_view: TurnItemsView::Summary,
@@ -2111,6 +2116,7 @@ fn append_agent_message(path: &Path, timestamp: &str, text: &str) -> anyhow::Res
                 phase: None,
                 memory_citation: None,
                 delivery: None,
+                questions: None,
             }))?,
         })
     )?;

codex-rs/app-server/tests/suite/v2/thread_resume.rs

@@ -3836,6 +3836,7 @@ async fn thread_resume_token_usage_replay_ignores_stale_interrupted_tail_turn()
                 phase: None,
                 memory_citation: None,
                 delivery: None,
+                questions: None,
             }))?,
         })
         .to_string(),
@@ -3923,6 +3924,7 @@ async fn thread_resume_token_usage_replay_can_belong_to_interrupted_turn() -> Re
                 phase: None,
                 memory_citation: None,
                 delivery: None,
+                questions: None,
             }))?,
         })
         .to_string(),
@@ -4233,6 +4235,7 @@ async fn thread_resume_and_read_interrupt_incomplete_rollout_turn_when_thread_is
                 phase: None,
                 memory_citation: None,
                 delivery: None,
+                questions: None,
             }))?,
         })
         .to_string(),