feat: add Nex and Gopher listeners

Reuses md2txt's existing nex and text renderers (both already ship
unmodified) -- rendered unwrapped gemtext still works for Gemini/Spartan
clients that wrap themselves, but Nex and Gopher clients don't, so those
two get the classic 80-column pre-wrap instead.

Neither protocol has a redirect status of its own, so Site.resolve_flat()
follows the /foo.md -> /foo canonical bounce and the WML-card-only ->
parent redirect server-side and hands back real content directly, rather
than leaving the two new listeners to invent a redirect convention that
doesn't exist on the wire.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_site.py

@@ -114,6 +114,58 @@ class TestWmlCardUrls:
         doc = site.resolve("/trail")
         assert b"{.card" not in doc.xhtml
 
+    def test_directive_line_does_not_leak_into_nex_or_gopher(self, site: Site):
+        doc = site.resolve("/trail")
+        assert b"{.card" not in doc.nex
+        assert b"{.card" not in doc.gopher
+        assert b"Cold and clear" in doc.nex
+        assert b"Cold and clear" in doc.gopher
+
+
+class TestNexAndGopherRendering:
+    def test_nex_and_gopher_fields_are_rendered(self, site: Site):
+        doc = site.resolve("/about")
+        assert isinstance(doc, Document)
+        assert b"About" in doc.nex
+        assert b"Body." in doc.nex
+        # md2txt's `text` renderer (unlike `nex`) still FIGlet-banners
+        # h1-h3 by default, so only plain paragraph text is checked here.
+        assert b"Body." in doc.gopher
+
+    def test_nex_heading_has_no_figlet_banner(self, site: Site):
+        # The nex renderer uses a plain setext-style underline, never a
+        # FIGlet banner -- unlike md2txt's own `text` renderer, which does
+        # use one for h1-h3 by default.
+        doc = site.resolve("/")
+        assert b"# Home" not in doc.nex
+        assert b"Home" in doc.nex
+        assert b"====" in doc.nex
+
+
+class TestResolveFlat:
+    def test_canonical_md_redirect_is_resolved_not_bounced(self, site: Site):
+        # Nex and Gopher have no redirect status: a request for the .md
+        # form must come back with the real document, not a Redirect.
+        resource = site.resolve_flat("/about.md")
+        assert isinstance(resource, Document)
+        assert b"About" in resource.nex
+
+    def test_unmatched_card_is_resolved_to_parent_document(self, site: Site):
+        resource = site.resolve_flat("/trail/nonexistent-card")
+        assert isinstance(resource, Document)
+        assert b"North: open" in resource.gopher
+
+    def test_card_subpath_is_resolved_to_parent_document_not_the_wml_card(self, site: Site):
+        # /trail/weather is WML-only URL space; resolve_flat must land on
+        # trail.md's own Document (which has .nex/.gopher), never leak a
+        # WmlCard (which has neither) out to the Nex/Gopher servers.
+        resource = site.resolve_flat("/trail/weather")
+        assert isinstance(resource, Document)
+
+    def test_still_raises_not_found_for_a_missing_path(self, site: Site):
+        with pytest.raises(NotFound):
+            site.resolve_flat("/nope")
+
 
 class TestHtmlFallbackHasNoXmlProlog:
     def test_html_field_has_no_prolog(self, site: Site):