Re-vendor the canonical files from sneak/prompts at dd4027b (closes #112)

The shared files are fetched from sneak/prompts dd4027b, with this
repository's own entries after the shared content in .gitignore,
.editorconfig and .dockerignore.

Lint and tests are Dockerfile phases (golangci-lint v2.14.0, Debian Go
1.24.13) that the build stage depends on, and the Makefile targets call
the script/ entrypoints. make fmt also formats Markdown with prettier.

Fixes for the new lint findings: the auth cookie is always Secure, an
IRC connection's relay goroutine stops when the connection closes, and
repeated strings are constants. neoirc-cli treats a plain-HTTP server on
localhost or a loopback address as secure, so local use keeps its session.

Whether the 60-second test cap covers building the test phase is open
on sneak/prompts issue 113.

Model: opus-5-5

internal/cli/api/client_test.go

@@ -0,0 +1,131 @@
+package neoircapi_test
+
+import (
+	"context"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	api "sneak.berlin/go/neoirc/internal/cli/api"
+)
+
+const cookieValue = "opaque-value"
+
+// newSessionServer starts a plain-HTTP server that, like
+// neoircd, sets a Secure auth cookie when a session is
+// created and answers GET /api/v1/state only when that
+// cookie comes back.
+func newSessionServer(t *testing.T) *httptest.Server {
+	t.Helper()
+
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("GET /api/v1/server", func(
+		writer http.ResponseWriter, _ *http.Request,
+	) {
+		_, _ = io.WriteString(writer, `{}`)
+	})
+
+	mux.HandleFunc("POST /api/v1/session", func(
+		writer http.ResponseWriter, _ *http.Request,
+	) {
+		http.SetCookie(writer, &http.Cookie{
+			Name:     "neoirc_auth",
+			Value:    cookieValue,
+			Path:     "/",
+			HttpOnly: true,
+			Secure:   true,
+			SameSite: http.SameSiteStrictMode,
+		})
+		writer.WriteHeader(http.StatusCreated)
+
+		_, _ = io.WriteString(writer, `{"id":1,"nick":"alice"}`)
+	})
+
+	mux.HandleFunc("GET /api/v1/state", func(
+		writer http.ResponseWriter, request *http.Request,
+	) {
+		cookie, err := request.Cookie("neoirc_auth")
+		if err != nil || cookie.Value != cookieValue {
+			writer.WriteHeader(http.StatusUnauthorized)
+
+			return
+		}
+
+		_, _ = io.WriteString(
+			writer, `{"id":1,"nick":"alice","channels":[]}`,
+		)
+	})
+
+	server := httptest.NewServer(mux)
+	t.Cleanup(server.Close)
+
+	return server
+}
+
+func TestClientKeepsSessionOverPlainHTTPOnLocalhost(t *testing.T) {
+	t.Parallel()
+
+	server := newSessionServer(t)
+
+	serverURL, err := url.Parse(server.URL)
+	if err != nil {
+		t.Fatalf("parse server URL: %v", err)
+	}
+
+	for _, host := range []string{"127.0.0.1", "localhost"} {
+		t.Run(host, func(t *testing.T) {
+			t.Parallel()
+
+			client := api.NewClient(
+				"http://" + net.JoinHostPort(host, serverURL.Port()),
+			)
+
+			_, err := client.CreateSession("alice")
+			if err != nil {
+				t.Fatalf("create session: %v", err)
+			}
+
+			_, err = client.GetState()
+			if err != nil {
+				t.Fatalf("state after creating the session: %v", err)
+			}
+		})
+	}
+}
+
+func TestClientWithholdsCookieOverPlainHTTPFromOtherHosts(t *testing.T) {
+	t.Parallel()
+
+	server := newSessionServer(t)
+
+	// neoirc.example is not loopback. Every connection the client
+	// opens to it goes to the test server instead.
+	client := api.NewClient("http://neoirc.example")
+	client.HTTPClient.Transport = &http.Transport{
+		DialContext: func(
+			ctx context.Context, network, _ string,
+		) (net.Conn, error) {
+			var dialer net.Dialer
+
+			return dialer.DialContext(
+				ctx, network, server.Listener.Addr().String(),
+			)
+		},
+	}
+
+	_, err := client.CreateSession("alice")
+	if err != nil {
+		t.Fatalf("create session: %v", err)
+	}
+
+	// The server answers 401 when the auth cookie does not arrive.
+	_, err = client.GetState()
+	if err == nil || !strings.Contains(err.Error(), "401") {
+		t.Fatalf("state: got %v, want 401: cookie sent over plain HTTP", err)
+	}
+}