fix: cap default markdown TTY width

docs/cli-reference.md

@@ -243,8 +243,9 @@ fetch --discard --timing example.com        # Measure timing only
 Control response formatting. Values: `auto`, `on`, `off`.
 
 Markdown rendered on a terminal uses clickable OSC 8 hyperlinks when the
-terminal supports them. Non-terminal output does not contain OSC 8 hyperlink
-escapes.
+terminal supports them. Terminal prose wraps to the detected terminal width,
+capped at 100 columns by default. Non-terminal output does not contain OSC 8
+hyperlink escapes.
 
 ```sh
 fetch --format off example.com   # Disable formatting

docs/output-formatting.md

@@ -173,7 +173,8 @@ Features:
 - Blockquote and list marker highlighting; TTY blockquotes use a muted rule
   and muted text
 - Bold blue table headers with dimmed table borders and separators
-- TTY prose wraps to the detected terminal width using display-cell widths;
+- TTY prose wraps to the detected terminal width, capped at 100 columns by
+  default, using display-cell widths;
   wide tables use a vertical record layout
 - On TTYs, links and image alt text are rendered as clickable OSC 8 terminal
   hyperlinks; non-terminal output does not contain OSC 8 hyperlink escapes

internal/format/markdown.go

@@ -18,13 +18,17 @@ import (
 	"github.com/yuin/goldmark/util"
 )
 
-const maxMarkdownBlockquoteOpeners = 256
+const (
+	maxMarkdownBlockquoteOpeners = 256
+	defaultMarkdownMaxWidth      = 100
+)
 
 // MarkdownOptions controls terminal-only Markdown presentation.
 //
 // MaxWidth is a maximum display width in terminal columns. A zero value uses
-// the current terminal width when the destination is a TTY. Non-terminal
-// output remains raw Markdown regardless of this value.
+// the smaller of the current terminal width and 100 columns when the
+// destination is a TTY. Non-terminal output remains raw Markdown regardless
+// of this value.
 type MarkdownOptions struct {
 	MaxWidth int
 }
@@ -62,18 +66,24 @@ func FormatMarkdownWithOptions(buf []byte, p *core.Printer, options MarkdownOpti
 
 	width := 0
 	if p.IsTerminal() {
-		width = options.MaxWidth
-		if terminalWidth := core.GetTerminalCols(); terminalWidth > 0 &&
-			(width <= 0 || terminalWidth < width) {
-			width = terminalWidth
-		}
+		width = markdownWidth(options.MaxWidth, core.GetTerminalCols())
 	}
 
 	r := &mdRenderer{printer: p, source: rest, width: width}
 	r.tty = p.IsTerminal()
 	return ast.Walk(doc, r.walk)
 }
 
+func markdownWidth(maxWidth, terminalWidth int) int {
+	if maxWidth <= 0 {
+		maxWidth = defaultMarkdownMaxWidth
+	}
+	if terminalWidth > 0 && terminalWidth < maxWidth {
+		return terminalWidth
+	}
+	return maxWidth
+}
+
 // truncateMarkdownBlockquoteOpeners caps line-leading blockquote opener runs.
 // Goldmark's container handling becomes quadratic at extreme nesting depths, so
 // discard openers beyond the largest depth that is useful for terminal output.

internal/format/markdown_test.go

@@ -768,6 +768,29 @@ func TestFormatMarkdownWrapsTerminalProseToDisplayWidth(t *testing.T) {
 	}
 }
 
+func TestMarkdownWidthDefaultsToTerminalWidthOr100(t *testing.T) {
+	tests := []struct {
+		name          string
+		maxWidth      int
+		terminalWidth int
+		want          int
+	}{
+		{name: "narrow terminal", terminalWidth: 80, want: 80},
+		{name: "wide terminal", terminalWidth: 120, want: 100},
+		{name: "terminal unavailable", want: 100},
+		{name: "explicit width", maxWidth: 40, terminalWidth: 120, want: 40},
+		{name: "explicit width capped by terminal", maxWidth: 120, terminalWidth: 80, want: 80},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := markdownWidth(tt.maxWidth, tt.terminalWidth); got != tt.want {
+				t.Fatalf("markdownWidth(%d, %d) = %d, want %d", tt.maxWidth, tt.terminalWidth, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestFormatMarkdownWrapsStyledLinkByVisibleWidth(t *testing.T) {
 	p := core.TestTerminalPrinter(false)
 	input := "[one two three four five](https://example.com/docs)"