fix(cli): restore progress bars on human format and check tty in auto mode (#4860)

[dlowzzxx]

Fixes #4860

Description

In auto output mode, AI agent detection (e.g. from terminals like Warp setting TERM_PROGRAM=WarpTerminal or other environment variables matching the agent harness registry) caused progress bars and ANSI colors to be silently disabled, even when running interactively in a user terminal. Additionally, when switching formats back to human via set_mode(OutputFormat.human), progress bars remained disabled because enable_progress_bars() was not called.

This PR addresses this with:

1. Defensive interactive TTY check in auto mode:
   In Output.set_mode(), when mode == OutputFormat.auto, we check if sys.stderr is interactive via is_interactive = bool(getattr(sys.stderr, "isatty", lambda: False)()). We only select OutputFormat.agent if is_agent() and not is_interactive; otherwise, interactive terminals resolve to OutputFormat.human.
2. Progress bar restoration:
   When mode == OutputFormat.human, enable_progress_bars() is called to re-enable progress bars if they had previously been disabled.
3. Interactive terminal color preservation:
   In ANSI._format(), colors are preserved if the terminal is interactive, only suppressing colors for agents in non-interactive environments (is_agent() and not bool(getattr(sys.stderr, "isatty", lambda: False)())).
4. Explicit set_mode(OutputFormat.agent) still forces agent mode regardless of TTY status.

Reproduction & Verification

• Prior to the fix, running test_set_mode_human_reenables_progress_bars, test_auto_resolves_to_human_in_interactive_terminal_even_if_agent, and test_ansi_agent_interactive_preserves_color failed with progress bars remaining disabled and mode resolving to agent in interactive sessions.
• Added comprehensive regression tests in tests/test_cli_output.py and tests/test_utils_terminal.py.
• Verified all unit tests pass:
  • uv run pytest tests/test_cli_output.py (36 passed)
  • uv run pytest tests/test_utils_detect_agent.py (17 passed)
  • uv run pytest tests/test_utils_terminal.py (6 passed)
  • uv run --with ruff ruff check src tests (clean)
  • uv run --with ruff ruff format --check src tests (clean)

---

Note

Low Risk
CLI output and TTY detection only; no auth, data handling, or API behavior changes.

Overview
Fixes agent auto-detection treating interactive terminals (e.g. Warp) like headless agent sessions, which turned off progress bars and ANSI styling even for real users.

Auto format now picks agent only when is_agent() is true and stderr is not a TTY; interactive sessions stay on human mode. Explicit --format agent still forces agent mode and disables bars.

Adds a defensive is_terminal() helper (used by Output, StatusLine, and ANSI) so isatty() on missing/closed streams does not crash. Human mode calls enable_progress_bars() again when switching back (unless HF_HUB_DISABLE_PROGRESS_BARS is set). ANSI keeps color in interactive terminals even when is_agent() is true; colors stay suppressed only for non-interactive agent runs.

Regression tests cover mode resolution, progress bar toggling, and ANSI behavior.

^{Reviewed by Cursor Bugbot for commit 87c0fb8. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit f333c9c. Configure here.}

[hanouticelina]

Hi @dlowzzxx, thanks for the PR! Closing in favor of #4878, which covers the progress bars / colors part in a slightly different way and we're not going with the tty check