[codex] Fix TUI wrapping for external borrowed slices

[canvrno-oai]

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

[canvrno-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

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[fcoury-oai]

I attempt to trigger the panic but couldn't, at least on macOS.

Code looks good, approved 👍