fix: truncate long approval prefixes when rendering (#8734)

Fixes inscrutable multiline approval requests:
<img width="686" height="844" alt="image"
src="https://github.com/user-attachments/assets/cf9493dc-79e6-4168-8020-0ef0fe676d5e"
/>

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

@@ -2465,6 +2465,48 @@ async fn approval_modal_exec_without_reason_snapshot() -> anyhow::Result<()> {
     Ok(())
 }
 
+// Snapshot test: approval modal with a proposed execpolicy prefix that is multi-line;
+// we should not offer adding it to execpolicy.
+#[tokio::test]
+async fn approval_modal_exec_multiline_prefix_hides_execpolicy_option_snapshot()
+-> anyhow::Result<()> {
+    let (mut chat, _rx, _op_rx) = make_chatwidget_manual(None).await;
+    chat.config.approval_policy.set(AskForApproval::OnRequest)?;
+
+    let script = "python - <<'PY'\nprint('hello')\nPY".to_string();
+    let command = vec!["bash".into(), "-lc".into(), script];
+    let ev = ExecApprovalRequestEvent {
+        call_id: "call-approve-cmd-multiline-trunc".into(),
+        turn_id: "turn-approve-cmd-multiline-trunc".into(),
+        command: command.clone(),
+        cwd: std::env::current_dir().unwrap_or_else(|_| PathBuf::from(".")),
+        reason: None,
+        proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(command)),
+        parsed_cmd: vec![],
+    };
+    chat.handle_codex_event(Event {
+        id: "sub-approve-multiline-trunc".into(),
+        msg: EventMsg::ExecApprovalRequest(ev),
+    });
+
+    let width = 100;
+    let height = chat.desired_height(width);
+    let mut terminal =
+        ratatui::Terminal::new(VT100Backend::new(width, height)).expect("create terminal");
+    terminal.set_viewport_area(Rect::new(0, 0, width, height));
+    terminal
+        .draw(|f| chat.render(f.area(), f.buffer_mut()))
+        .expect("draw approval modal (multiline prefix)");
+    let contents = terminal.backend().vt100().screen().contents();
+    assert!(!contents.contains("don't ask again"));
+    assert_snapshot!(
+        "approval_modal_exec_multiline_prefix_no_execpolicy",
+        contents
+    );
+
+    Ok(())
+}
+
 // Snapshot test: patch approval modal
 #[tokio::test]
 async fn approval_modal_patch_snapshot() -> anyhow::Result<()> {