feat: add Instance endpoint value object

internal/domain/instance/endpoint.go

@@ -0,0 +1,89 @@
+/*
+Copyright 2026.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package instance contains the pure domain model of a registered PostgreSQL instance.
+// It does not depend on Kubernetes types, database drivers or credential providers.
+package instance
+
+import (
+	"errors"
+	"net/netip"
+	"regexp"
+)
+
+// TLSMode is an explicit transport policy, not a driver-specific default.
+type TLSMode string
+
+const (
+	TLSDisable    TLSMode = "disable"
+	TLSRequire    TLSMode = "require"
+	TLSVerifyCA   TLSMode = "verify-ca"
+	TLSVerifyFull TLSMode = "verify-full"
+)
+
+// EndpointValues carries explicit, effective values across the application boundary.
+// Defaults are supplied by the API/application mapping, never silently by the domain.
+type EndpointValues struct {
+	Host               string
+	HostAddr           string
+	Port               int
+	ManagementDatabase string
+	TLSMode            TLSMode
+}
+
+// Endpoint is an immutable connection target. Equality compares its declared values,
+// not physical server identity. Its zero value is invalid; aggregate construction
+// must Validate incoming endpoints, even if callers bypass NewEndpoint.
+type Endpoint struct {
+	values EndpointValues
+}
+
+var identifier = regexp.MustCompile(`^[a-z][a-z0-9_]{0,62}$`)
+
+func NewEndpoint(values EndpointValues) (Endpoint, error) {
+	endpoint := Endpoint{values: values}
+	if err := endpoint.Validate(); err != nil {
+		return Endpoint{}, err
+	}
+	return endpoint, nil
+}
+
+// Values returns a copy, without exposing mutable state.
+func (e Endpoint) Values() EndpointValues { return e.values }
+
+// Validate checks local invariants only; it does not resolve DNS or perform IO.
+// Errors intentionally omit input values.
+func (e Endpoint) Validate() error {
+	if e.values.Host == "" {
+		return errors.New("endpoint host is required")
+	}
+	address, err := netip.ParseAddr(e.values.HostAddr)
+	if err != nil || address.Zone() != "" {
+		return errors.New("endpoint host address must be an IPv4 or IPv6 address")
+	}
+	if e.values.Port < 1 || e.values.Port > 65535 {
+		return errors.New("endpoint port must be between 1 and 65535")
+	}
+	if !identifier.MatchString(e.values.ManagementDatabase) {
+		return errors.New("endpoint management database must be a valid PostgreSQL identifier")
+	}
+	switch e.values.TLSMode {
+	case TLSDisable, TLSRequire, TLSVerifyCA, TLSVerifyFull:
+		return nil
+	default:
+		return errors.New("endpoint TLS mode must be explicitly supported")
+	}
+}