Show multiline command previews in /ps (#48101)

## Why

`/ps` previously showed only the first line of each background command, hiding useful details when a command began with an opening parenthesis.

## What changed

Render LF and CRLF line breaks as `↵` in command previews. Include subsequent lines within the existing 80-grapheme limit, and show the truncation marker only when the command exceeds that limit.

## Testing

Update snapshot coverage for multiline commands, including parenthesized commands and CRLF line endings, and add a snapshot for a multiline command exceeding the preview limit.

GitOrigin-RevId: 92544e5636821fc94bc1ca4af389c3c646127c0e

codex-rs/tui/src/history_cell/exec.rs

@@ -159,17 +159,17 @@ impl HistoryCell for UnifiedExecProcessesCell {
             }
             let command = &process.command_display;
             let (snippet, snippet_truncated) = {
-                let (first_line, has_more_lines) = match command.split_once('\n') {
-                    Some((first, _)) => (first, true),
-                    None => (command.as_str(), false),
-                };
                 let max_graphemes = 80;
-                let mut graphemes = first_line.grapheme_indices(true);
-                if let Some((byte_index, _)) = graphemes.nth(max_graphemes) {
-                    (first_line[..byte_index].to_string(), true)
-                } else {
-                    (first_line.to_string(), has_more_lines)
-                }
+                let mut graphemes = command.graphemes(true);
+                let snippet: String = graphemes
+                    .by_ref()
+                    .take(max_graphemes)
+                    .map(|grapheme| match grapheme {
+                        "\n" | "\r\n" => "↵",
+                        _ => grapheme,
+                    })
+                    .collect();
+                (snippet, graphemes.next().is_some())
             };
             if wrap_width <= prefix_width {
                 out.push(Line::from(prefix.dim()));

codex-rs/tui/src/history_cell/snapshots/codex_tui__history_cell__tests__ps_output_multiline_long_command_snapshot.snap

@@ -0,0 +1,9 @@
+---
+source: tui/src/history_cell/tests.rs
+expression: rendered
+---
+/ps
+
+Background terminals
+
+  • (↵  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx [...]

codex-rs/tui/src/history_cell/snapshots/codex_tui__history_cell__tests__ps_output_multiline_snapshot.snap

@@ -1,13 +1,15 @@
 ---
-source: tui/src/history_cell.rs
+source: tui/src/history_cell/tests.rs
 expression: rendered
 ---
 /ps
 
 Background terminals
 
-  • echo hello [...]
+  • echo hello↵and then some extra text
     ↳ hello
       done
+  • (↵  sleep 120↵)
+  • sleep 1↵sleep 120
   • rg "foo" src
     ↳ src/main.rs:12:foo

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

@@ -878,6 +878,14 @@ fn ps_output_multiline_snapshot() {
             command_display: "echo hello\nand then some extra text".to_string(),
             recent_chunks: vec!["hello".to_string(), "done".to_string()],
         },
+        UnifiedExecProcessDetails {
+            command_display: "(\n  sleep 120\n)".to_string(),
+            recent_chunks: Vec::new(),
+        },
+        UnifiedExecProcessDetails {
+            command_display: "sleep 1\r\nsleep 120".to_string(),
+            recent_chunks: Vec::new(),
+        },
         UnifiedExecProcessDetails {
             command_display: "rg \"foo\" src".to_string(),
             recent_chunks: vec!["src/main.rs:12:foo".to_string()],
@@ -887,6 +895,16 @@ fn ps_output_multiline_snapshot() {
     insta::assert_snapshot!(rendered);
 }
 
+#[test]
+fn ps_output_multiline_long_command_snapshot() {
+    let cell = new_unified_exec_processes_output(vec![UnifiedExecProcessDetails {
+        command_display: format!("(\n  {}\n)", "x".repeat(100)),
+        recent_chunks: Vec::new(),
+    }]);
+    let rendered = render_lines(&cell.display_lines(/*width*/ 100)).join("\n");
+    insta::assert_snapshot!(rendered);
+}
+
 #[test]
 fn cyber_policy_error_event_snapshot() {
     let cell = new_cyber_policy_error_event(crate::daybreak::Notice::Apply);