feat: add Go migration compatibility foundation

backend/internal/postgres/open_test.go

@@ -0,0 +1,62 @@
+package postgres
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+func TestOpenLocalReturnsStoreWithoutPool(t *testing.T) {
+	module, err := Open(context.Background(), Config{Backend: BackendLocal})
+	if err != nil {
+		t.Fatalf("Open() error = %v", err)
+	}
+	if module.Store == nil {
+		t.Fatal("Store = nil")
+	}
+	module.Close()
+	if err := module.Store.Readiness(context.Background()); err != nil {
+		t.Fatalf("Readiness() error = %v", err)
+	}
+}
+
+func TestOpenPostgresDoesNotProbeBeforeReadiness(t *testing.T) {
+	module, err := Open(context.Background(), Config{
+		Backend:         BackendPostgres,
+		DatabaseURL:     "postgresql://app:secret@127.0.0.1:1/app",
+		SSLMode:         SSLDisable,
+		PoolMax:         1,
+		ApplicationName: "zhinian-go-test",
+	})
+	if err != nil {
+		t.Fatalf("Open() error = %v; connection failures belong to readiness", err)
+	}
+	module.Close()
+}
+
+func TestParseConfigIgnoresPostgresTLSSettingsForLocalBackend(t *testing.T) {
+	cfg, err := ParseConfig(env(map[string]string{
+		"ZHINIAN_DATA_BACKEND":           "local",
+		"DATABASE_SSL_MODE":              "verify-full",
+		"DATABASE_CA_CERT_PATH":          "/missing/ca.pem",
+		"DATABASE_POOL_MAX":              "0",
+		"DATABASE_CONNECTION_TIMEOUT_MS": "invalid",
+	}), nil)
+	if err != nil {
+		t.Fatalf("ParseConfig() error = %v", err)
+	}
+	if cfg.Backend != BackendLocal || cfg.TLSConfig != nil {
+		t.Fatalf("config = %+v", cfg)
+	}
+}
+
+func TestOpenPostgresRejectsInvalidConfiguredTLSMode(t *testing.T) {
+	_, err := Open(context.Background(), Config{
+		Backend:     BackendPostgres,
+		DatabaseURL: "postgresql://app:secret@db.example/app",
+		SSLMode:     SSLMode("prefer"),
+	})
+	if err == nil || !strings.Contains(err.Error(), "DATABASE_SSL_MODE") {
+		t.Fatalf("Open() error = %v", err)
+	}
+}