[codex] Fix TUI wrapping for external borrowed slices (#21235)

Fixes #20587, reported by @noeljackson.

This prevents the TUI wrapping code from panicking when `textwrap`
returns a borrowed slice that does not point into the original source
text. The fix follows the direction proposed by @misrtjakub in the issue
comment: validate the borrowed slice pointer range first, and fall back
to the existing owned-line mapper when the slice is external.

- Guards borrowed wrapped slices before converting pointer offsets into
byte ranges.
- Reuses the existing owned-line range recovery path for external
borrowed slices.
- Adds coverage for rejecting borrowed slices outside the source text.

End-user testing steps:
- Start Codex in TUI mode under a PTY wrapper that can inject stdin
after startup.
- Inject `\x1b[200~test message\x1b[201~\r` after the TUI is ready.
- Confirm Codex does not panic and the pasted text is handled normally.

Local validation:
- `cargo test -p codex-tui wrapping::tests::`
- `cargo test -p codex-tui -- --skip
status::tests::status_permissions_full_disk_managed_with_network_is_danger_full_access
--skip
status::tests::status_permissions_full_disk_managed_without_network_is_external_sandbox`

codex-rs/tui/src/wrapping.rs

@@ -49,8 +49,16 @@ where
     for (line_index, line) in textwrap::wrap(text, &opts).iter().enumerate() {
         match line {
             std::borrow::Cow::Borrowed(slice) => {
-                let start = unsafe { slice.as_ptr().offset_from(text.as_ptr()) as usize };
-                let end = start + slice.len();
+                let range = borrowed_slice_range(text, slice).unwrap_or_else(|| {
+                    let synthetic_prefix = if line_index == 0 {
+                        opts.initial_indent
+                    } else {
+                        opts.subsequent_indent
+                    };
+                    map_owned_wrapped_line_to_range(text, cursor, slice, synthetic_prefix)
+                });
+                let start = range.start;
+                let end = range.end;
                 let trailing_spaces = text[end..].chars().take_while(|c| *c == ' ').count();
                 lines.push(start..end + trailing_spaces + 1);
                 cursor = end + trailing_spaces;
@@ -84,10 +92,16 @@ where
     for (line_index, line) in textwrap::wrap(text, &opts).iter().enumerate() {
         match line {
             std::borrow::Cow::Borrowed(slice) => {
-                let start = unsafe { slice.as_ptr().offset_from(text.as_ptr()) as usize };
-                let end = start + slice.len();
-                lines.push(start..end);
-                cursor = end;
+                let range = borrowed_slice_range(text, slice).unwrap_or_else(|| {
+                    let synthetic_prefix = if line_index == 0 {
+                        opts.initial_indent
+                    } else {
+                        opts.subsequent_indent
+                    };
+                    map_owned_wrapped_line_to_range(text, cursor, slice, synthetic_prefix)
+                });
+                cursor = range.end;
+                lines.push(range);
             }
             std::borrow::Cow::Owned(slice) => {
                 let synthetic_prefix = if line_index == 0 {
@@ -104,6 +118,19 @@ where
     lines
 }
 
+fn borrowed_slice_range(text: &str, slice: &str) -> Option<Range<usize>> {
+    let text_start = text.as_ptr() as usize;
+    let text_end = text_start.checked_add(text.len())?;
+    let slice_start = slice.as_ptr() as usize;
+    let slice_end = slice_start.checked_add(slice.len())?;
+
+    if slice_start < text_start || slice_end > text_end {
+        return None;
+    }
+
+    Some((slice_start - text_start)..(slice_end - text_start))
+}
+
 /// Maps an owned (materialized) wrapped line back to a byte range in `text`.
 ///
 /// `textwrap` returns `Cow::Owned` when it inserts a hyphenation penalty
@@ -1485,6 +1512,17 @@ them."#
         assert_eq!(range, 0..5);
     }
 
+    #[test]
+    fn borrowed_slice_range_rejects_slices_outside_source_text() {
+        let text = "test message";
+        let external = String::from("test");
+
+        assert_eq!(borrowed_slice_range(text, &external), None);
+
+        let fallback = map_owned_wrapped_line_to_range(text, /*cursor*/ 0, &external, "");
+        assert_eq!(fallback, 0..4);
+    }
+
     #[test]
     fn map_owned_wrapped_line_to_range_indent_coincides_with_source() {
         // When the synthetic indent prefix starts with a character that also