Add himalaya + meli mail clients and Shedding Snake arcade game (#88)

Mail clients (internal/mailclients): launch himalaya and meli as
alternatives to the built-in AgentMail reader, pointed at the member's
mailbox with the same master IMAP / loopback-SMTP creds. They run
host-side (secrets never enter a pod), from a throwaway per-session
config that is deleted on exit; operators can override the config
template and argv via env. Wired into the hub ("Mail · Himalaya/Meli",
locked when the binary is absent) and the mail@ route
(ssh -t mail@host himalaya|meli).

Shedding Snake (plugins/arcade): a molting twist on Snake inspired by
cha.rlie.co/shedding-snake. The snake barely grows — each apple sheds
its whole body as a permanent field of scales you must not bite. Walls
wrap, speed ramps up, scales age fresh-teal → dusty-gray, and molt
counts feed a global "shedsnake" leaderboard. Grace period lets you
slither off a fresh molt.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

internal/mailclients/mailclients_test.go

@@ -0,0 +1,126 @@
+package mailclients
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func testBackend() Backend {
+	return Backend{
+		Name:          "alice",
+		Address:       "alice@bbs.profullstack.com",
+		DisplayName:   "alice",
+		IMAPHost:      "127.0.0.1",
+		IMAPPort:      143,
+		IMAPPlaintext: true,
+		SMTPHost:      "127.0.0.1",
+		SMTPPort:      25,
+		SMTPPlaintext: true,
+		Login:         "alice@bbs.profullstack.com*gateway",
+		Password:      "s3cr3t",
+	}
+}
+
+func TestHimalayaTemplateRenders(t *testing.T) {
+	out := render(Himalaya.template, testBackend().placeholders())
+	for _, want := range []string{
+		`email = "alice@bbs.profullstack.com"`,
+		`backend.host = "127.0.0.1"`,
+		`backend.port = 143`,
+		`backend.encryption.type = "none"`, // plaintext IMAP
+		`backend.login = "alice@bbs.profullstack.com*gateway"`,
+		`backend.auth.raw = "s3cr3t"`,
+		`message.send.backend.port = 25`,
+		`message.send.backend.encryption.type = "none"`, // loopback relay
+	} {
+		if !strings.Contains(out, want) {
+			t.Errorf("himalaya config missing %q\n---\n%s", want, out)
+		}
+	}
+	// No placeholder should survive rendering.
+	if strings.Contains(out, "{{") {
+		t.Errorf("unrendered placeholder in himalaya config:\n%s", out)
+	}
+}
+
+func TestMeliTemplateRenders(t *testing.T) {
+	out := render(Meli.template, testBackend().placeholders())
+	for _, want := range []string{
+		`identity = "alice@bbs.profullstack.com"`,
+		`server_hostname = "127.0.0.1"`,
+		`server_username = "alice@bbs.profullstack.com*gateway"`,
+		`server_password = "s3cr3t"`,
+		`server_port = 143`,
+		`port = 25`,
+		`type = "none"`,
+	} {
+		if !strings.Contains(out, want) {
+			t.Errorf("meli config missing %q\n---\n%s", want, out)
+		}
+	}
+	if strings.Contains(out, "{{") {
+		t.Errorf("unrendered placeholder in meli config:\n%s", out)
+	}
+}
+
+func TestEncryptionSwitchesWithTLS(t *testing.T) {
+	be := testBackend()
+	be.IMAPPlaintext = false
+	be.SMTPPlaintext = false
+	out := render(Himalaya.template, be.placeholders())
+	if !strings.Contains(out, `backend.encryption.type = "tls"`) {
+		t.Errorf("expected tls IMAP encryption, got:\n%s", out)
+	}
+	if !strings.Contains(out, `message.send.backend.encryption.type = "start-tls"`) {
+		t.Errorf("expected start-tls SMTP encryption, got:\n%s", out)
+	}
+}
+
+func TestConfigTemplateOverride(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "tmpl-*.toml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := f.WriteString("custom {{address}}\n"); err != nil {
+		t.Fatal(err)
+	}
+	_ = f.Close()
+	t.Setenv(Himalaya.tmplEnv, f.Name())
+
+	tmpl, err := Himalaya.configTemplate()
+	if err != nil {
+		t.Fatal(err)
+	}
+	out := render(tmpl, testBackend().placeholders())
+	if out != "custom alice@bbs.profullstack.com\n" {
+		t.Errorf("override not used, got %q", out)
+	}
+}
+
+func TestArgvOverride(t *testing.T) {
+	// Default argv places -c <config>.
+	got := Meli.argv("/usr/bin/meli", "/cfg/x.toml")
+	want := []string{"/usr/bin/meli", "-c", "/cfg/x.toml"}
+	if strings.Join(got, " ") != strings.Join(want, " ") {
+		t.Errorf("default argv = %v, want %v", got, want)
+	}
+
+	// Override with a {{config}} placeholder.
+	t.Setenv(Meli.argsEnv, "--config {{config}} envelope list")
+	got = Meli.argv("/usr/bin/meli", "/cfg/x.toml")
+	want = []string{"/usr/bin/meli", "--config", "/cfg/x.toml", "envelope", "list"}
+	if strings.Join(got, " ") != strings.Join(want, " ") {
+		t.Errorf("override argv = %v, want %v", got, want)
+	}
+}
+
+func TestBinaryEnvOverrideMissing(t *testing.T) {
+	t.Setenv(Himalaya.binEnv, "/nonexistent/himalaya-binary")
+	if _, err := Himalaya.binary(); err == nil {
+		t.Error("expected error for missing binary override")
+	}
+	if Himalaya.Available() {
+		t.Error("Available() should be false when the override path is missing")
+	}
+}