fix: preserve ANSI colors when piping to pager on Windows

[VoidChecksum]

Summary

Fixes #799 — --pretty=all output loses colors when piped to a pager (less -r, more, etc.) on Windows.

Root cause

On Windows, HTTPie wraps stdout through colorama to translate ANSI escape codes into Win32 console API calls. When stdout is piped (not a TTY), colorama detects the non-TTY stream and strips all ANSI escape codes instead of passing them through.

The condition on writer.py line 49 routes through write_stream_with_colors_win() whenever colors are requested on Windows — even when stdout is piped to a pager. That function writes decoded text through colorama's wrapper, which strips the ANSI codes.

The regular write_stream() path writes raw bytes directly to outfile.buffer, bypassing colorama's text-layer stripping entirely — so ANSI codes pass through to the pipe intact.

Fix

Added env.stdout_isatty to the condition:

# Before
if env.is_windows and 'colors' in processing_options.get_prettify(env):

# After
if env.is_windows and env.stdout_isatty and 'colors' in processing_options.get_prettify(env):

write_stream_with_colors_win() is now only used when stdout is an actual terminal. When piped, the standard write_stream() path handles output — writing raw bytes with ANSI codes intact, letting pagers like less -r render colors correctly.

Platform impact

Scenario	Before	After
Windows, terminal	colorama translates ANSI → Win32	No change
Windows, piped to pager	colorama strips ANSI codes	ANSI codes pass through to pager
Linux/macOS	is_windows is False, path never entered	No change

Testing

Verified on Windows 10 with less via Git for Windows:

http --pretty=all https://httpbin.org/get | less -r

• Before: monochrome output, all colors stripped
• After: fully colored output rendered by less -r

[Copilot]

Pull request overview

Fixes a Windows-specific color handling issue where --pretty=all output loses ANSI colors when stdout is piped to a pager by avoiding the colorama text wrapper when stdout is not a TTY.

Changes:

• Gate the Windows write_stream_with_colors_win() path behind env.stdout_isatty so it’s only used for real terminals.
• Allow piped/redirected Windows output to go through write_stream() (raw bytes), preserving ANSI escape sequences for pagers like less -r.

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[Copilot]

Add a regression test for this Windows-specific branch selection: when env.is_windows is true, colors are requested (e.g. --pretty=all), and env.stdout_isatty is false (piped/redirected), we should use the raw write_stream() path (and not write_stream_with_colors_win()) so ANSI escape codes are preserved. Without a test, this behavior is easy to accidentally regress and reintroduce the color-stripping issue reported in #799.