tty: add IsStdoutTerminal, StderrTerminalWidth, and IsInteractiveTerminal

[Copilot]

Addresses the improvement opportunities from the go-fan module review of golang.org/x/term (#issue).

Changes

internal/tty/tty.go

• IsStdoutTerminal() — symmetric wrapper to IsStderrTerminal(), useful for detecting piped stdout in future CLI output formatting
• StderrTerminalWidth() — returns terminal width via term.GetSize; returns (0, false) when stderr is not a terminal or width cannot be determined
• IsInteractiveTerminal() — unified signal combining IsStderrTerminal() && !IsRunningInContainer(); provides a single predicate for "output is definitely going to a human terminal"

internal/tty/tty_test.go

• Tests for IsStdoutTerminal (agreement with term.IsTerminal)
• TestTermIsTerminal_PipeIsNotTerminal — documents that pipe fds return false from term.IsTerminal, validating the invariant both wrappers rely on
• Tests for StderrTerminalWidth — verifies width>0 only when stderr is a terminal, and 0/false in CI
• Tests for IsInteractiveTerminal — verifies it equals IsStderrTerminal() && !IsRunningInContainer(), and is false in CI

Security Summary

No security vulnerabilities introduced. CodeQL: 0 alerts.

[Copilot]

Pull request overview

This PR extends the internal/tty helpers to provide additional terminal/TTY predicates and terminal width detection, enabling callers to make more reliable decisions about human-facing CLI output formatting.

Changes:

• Add IsStdoutTerminal() as a stdout counterpart to IsStderrTerminal().
• Add StderrTerminalWidth() to retrieve stderr terminal width via golang.org/x/term.
• Add IsInteractiveTerminal() as a single predicate combining “stderr is a terminal” and “not running in a container”, plus corresponding tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/tty/tty.go	Adds new exported helpers for stdout terminal detection, stderr terminal width, and an “interactive terminal” predicate.
internal/tty/tty_test.go	Adds unit tests covering the new helpers and documents term.IsTerminal behavior for pipe FDs.

Comments suppressed due to low confidence (2)

internal/tty/tty_test.go:97

• This CI-specific test assumes CI/GITHUB_ACTIONS implies a non-terminal stderr. That’s not guaranteed across CI providers or when running tests locally with CI=1, and can make the test fail spuriously. Consider checking term.IsTerminal(int(os.Stderr.Fd())) and skipping if stderr is actually a terminal, or directly asserting !IsStderrTerminal() before the interactive check.

	if os.Getenv("CI") == "" && os.Getenv("GITHUB_ACTIONS") == "" {
		t.Skip("Skipping CI-specific assertion: not running in a CI environment")
	}
	assert.False(t, IsInteractiveTerminal(), "should not be interactive in CI")

internal/tty/tty_test.go:69

• TestStderrTerminalWidth assumes that if term.IsTerminal(stderr) is true then StderrTerminalWidth() must succeed. The function’s contract is “true if successful”, but term.GetSize can legitimately fail (or return non-positive width) even when IsTerminal is true (e.g., some CI/pseudo-TTYs, Windows/remote environments), which would make this test flaky. Consider asserting weaker invariants: when ok is true, width must be >0 and stderr must be a terminal; when ok is false, width must be 0 (and don’t fail solely because IsTerminal is true).

func TestStderrTerminalWidth(t *testing.T) {
	width, ok := StderrTerminalWidth()
	isTerminal := term.IsTerminal(int(os.Stderr.Fd()))
	if isTerminal {
		assert.True(t, ok, "should succeed when stderr is a terminal")
		assert.Greater(t, width, 0, "terminal width should be positive")
	} else {
		assert.False(t, ok, "should fail when stderr is not a terminal")
		assert.Equal(t, 0, width, "width should be 0 when not a terminal")
	}

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