Add markdown response body formatter

Line-oriented formatter with inline span parsing for text/markdown
responses. Supports ATX headings, fenced code blocks (with delegation
to JSON/YAML/XML/HTML/CSS formatters), blockquotes, ordered and
unordered lists, horizontal rules, and inline formatting (bold, italic,
code spans, links, images).

Author: ryanfowler

README.md

@@ -6,7 +6,7 @@ A modern HTTP(S) client for the command line.
 
 ## Features
 
-- **Response formatting** - Automatic formatting and syntax highlighting for JSON, XML, YAML, HTML, CSS, CSV, MessagePack, Protocol Buffers, and more
+- **Response formatting** - Automatic formatting and syntax highlighting for JSON, XML, YAML, HTML, CSS, CSV, Markdown, MessagePack, Protocol Buffers, and more
 - **Image rendering** - Display images directly in your terminal
 - **WebSocket support** - Bidirectional WebSocket connections with automatic JSON formatting
 - **gRPC support** - Make gRPC calls with automatic JSON-to-protobuf conversion

docs/output-formatting.md

@@ -137,6 +137,20 @@ Features:
 fetch example.com/styles.css
 ```
 
+### Markdown
+
+**Content-Types**: `text/markdown`, `text/x-markdown`
+
+Features:
+
+- Syntax highlighting for headings, bold, italic, code spans, links, images
+- Fenced code block delegation to JSON, YAML, XML, HTML, CSS formatters
+- Blockquote and list marker highlighting
+
+```sh
+fetch example.com/README.md
+```
+
 ### CSV
 
 **Content-Types**: `text/csv`, `application/csv`

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/mattn/go-runewidth v0.0.19
 	github.com/quic-go/quic-go v0.59.0
 	github.com/tinylib/msgp v1.6.3
+	github.com/yuin/goldmark v1.7.16
 	golang.org/x/crypto v0.48.0
 	golang.org/x/image v0.36.0
 	golang.org/x/net v0.50.0

go.sum

@@ -24,6 +24,8 @@ github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/tinylib/msgp v1.6.3 h1:bCSxiTz386UTgyT1i0MSCvdbWjVW+8sG3PjkGsZQt4s=
 github.com/tinylib/msgp v1.6.3/go.mod h1:RSp0LW9oSxFut3KzESt5Voq4GVWyS+PSulT77roAqEA=
+github.com/yuin/goldmark v1.7.16 h1:n+CJdUxaFMiDUNnWC3dMWCIQJSkxH4uz3ZwQBkAlVNE=
+github.com/yuin/goldmark v1.7.16/go.mod h1:ip/1k0VRfGynBgxOz0yCqHrbZXhcjxyuS66Brc7iBKg=
 go.uber.org/mock v0.5.2 h1:LbtPTcP8A5k9WPXj54PPPbjcI4Y6lhyOZXn+VS7wNko=
 go.uber.org/mock v0.5.2/go.mod h1:wLlUxC2vVTPTaE3UD51E0BGOAElKrILxhVSDYQLld5o=
 golang.org/x/crypto v0.48.0 h1:/VRzVqiRSggnhY7gNRxPauEQ5Drw9haKdM0jqfcCFts=

internal/format/contenttype.go

@@ -18,6 +18,7 @@ const (
 	TypeHTML
 	TypeImage
 	TypeJSON
+	TypeMarkdown
 	TypeMsgPack
 	TypeNDJSON
 	TypeProtobuf
@@ -82,6 +83,8 @@ func GetContentType(headers http.Header) (ContentType, string) {
 				return TypeCSV, charset
 			case "html":
 				return TypeHTML, charset
+			case "markdown", "x-markdown":
+				return TypeMarkdown, charset
 			case "event-stream":
 				return TypeSSE, charset
 			case "xml":