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/ircserver/server_test.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net"
 	"os"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -71,7 +72,9 @@ func newTestEnv(t *testing.T) *testEnv {
 		MOTD:       "Welcome to test IRC",
 	}
 
-	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	var listenConfig net.ListenConfig
+
+	listener, err := listenConfig.Listen(t.Context(), "tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatalf("listen: %v", err)
 	}
@@ -116,10 +119,12 @@ func newTestEnv(t *testing.T) *testEnv {
 func (env *testEnv) dial(t *testing.T) *testClient {
 	t.Helper()
 
-	conn, err := net.DialTimeout(
+	dialer := net.Dialer{Timeout: testTimeout}
+
+	conn, err := dialer.DialContext(
+		t.Context(),
 		"tcp",
 		env.srv.Listener().Addr().String(),
-		testTimeout,
 	)
 	if err != nil {
 		t.Fatalf("dial: %v", err)
@@ -323,6 +328,7 @@ func TestPrivmsgBetweenClients(t *testing.T) {
 	bob.joinAndDrain("#chat")
 
 	alice.send("PRIVMSG #chat :hello bob!")
+
 	lines := bob.sendAndExpect("PING :sync", "hello bob!")
 	assertContains(t, lines, "hello bob!", "channel PRIVMSG")
 }
@@ -603,6 +609,56 @@ func TestNamesNonExistentChannel(t *testing.T) {
 	)
 }
 
+// TestRelayStopsWhenConnectionCloses checks that closing a
+// registered client's connection stops the goroutine that
+// relays its messages.
+//
+//nolint:paralleltest // counts every goroutine in the process
+func TestRelayStopsWhenConnectionCloses(t *testing.T) {
+	env := newTestEnv(t)
+	client := env.dial(t)
+
+	client.register("relaystop")
+	waitForRelayGoroutines(t, 1)
+
+	err := client.conn.Close()
+	if err != nil {
+		t.Fatalf("close: %v", err)
+	}
+
+	waitForRelayGoroutines(t, 0)
+}
+
+const (
+	stackDumpSize  = 1 << 20
+	relayCheckStep = 10 * time.Millisecond
+)
+
+// waitForRelayGoroutines waits until exactly want goroutines
+// are running the relay loop, and fails the test if that does
+// not happen within testTimeout.
+func waitForRelayGoroutines(t *testing.T, want int) {
+	t.Helper()
+
+	deadline := time.Now().Add(testTimeout)
+	stacks := make([]byte, stackDumpSize)
+
+	for {
+		n := runtime.Stack(stacks, true)
+		got := strings.Count(string(stacks[:n]), "(*Conn).relayMessages(")
+
+		if got == want {
+			return
+		}
+
+		if time.Now().After(deadline) {
+			t.Fatalf("relay goroutines: got %d, want %d", got, want)
+		}
+
+		time.Sleep(relayCheckStep)
+	}
+}
+
 func BenchmarkParseMessage(b *testing.B) {
 	line := ":nick!user@host PRIVMSG #channel :Hello, world!"