feat(crypto): AES-256-GCM field encryption keyed from EMCLI_KEY

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/crypto/crypto_test.go

@@ -0,0 +1,69 @@
+package crypto
+
+import (
+	"bytes"
+	"encoding/base64"
+	"testing"
+)
+
+func testKey() []byte {
+	k := make([]byte, 32)
+	for i := range k {
+		k[i] = byte(i)
+	}
+	return k
+}
+
+func TestSealOpenRoundTrip(t *testing.T) {
+	key := testKey()
+	msg := []byte("hunter2-the-password")
+	blob, err := Seal(key, msg)
+	if err != nil {
+		t.Fatalf("Seal: %v", err)
+	}
+	if bytes.Contains(blob, msg) {
+		t.Fatal("ciphertext must not contain plaintext")
+	}
+	got, err := Open(key, blob)
+	if err != nil {
+		t.Fatalf("Open: %v", err)
+	}
+	if !bytes.Equal(got, msg) {
+		t.Fatalf("round-trip mismatch: %q", got)
+	}
+}
+
+func TestSealUsesRandomNonce(t *testing.T) {
+	key := testKey()
+	a, _ := Seal(key, []byte("x"))
+	b, _ := Seal(key, []byte("x"))
+	if bytes.Equal(a, b) {
+		t.Fatal("two seals of same plaintext must differ (random nonce)")
+	}
+}
+
+func TestOpenWrongKeyFails(t *testing.T) {
+	blob, _ := Seal(testKey(), []byte("secret"))
+	wrong := make([]byte, 32) // all zeros
+	if _, err := Open(wrong, blob); err == nil {
+		t.Fatal("Open with wrong key must fail")
+	}
+}
+
+func TestKeyFromEnv(t *testing.T) {
+	t.Setenv("EMCLI_KEY", base64.StdEncoding.EncodeToString(testKey()))
+	k, err := KeyFromEnv()
+	if err != nil || len(k) != 32 {
+		t.Fatalf("KeyFromEnv: key=%d err=%v", len(k), err)
+	}
+
+	t.Setenv("EMCLI_KEY", "")
+	if _, err := KeyFromEnv(); err != ErrNoKey {
+		t.Fatalf("empty key: want ErrNoKey, got %v", err)
+	}
+
+	t.Setenv("EMCLI_KEY", base64.StdEncoding.EncodeToString([]byte("tooshort")))
+	if _, err := KeyFromEnv(); err != ErrBadKey {
+		t.Fatalf("short key: want ErrBadKey, got %v", err)
+	}
+}