The original PR #17194 description claimed test_display_tool_preview.py
but only ever shipped test_display_todo_progress.py. Add the missing
coverage for the failure-suffix path:
- _trim_error: whitespace strip, length cap, File-not-found path collapse
- _detect_tool_failure: terminal exit codes, memory full, structured
{error}/{message} extraction, malformed JSON, None result
- get_cute_tool_message E2E: read_file failure, terminal exit-only,
terminal stderr message, memory full, success path, no-result path
Also update test_tool_progress_scrollback.test_error_suffix_on_failed_tool
to reflect the new behavior: the generic '[error]' fallback in cli.py
has been removed; failure suffixes now come from the result-aware
_detect_tool_failure (e.g. '[exit 1]', '[File not found: x]').
