feat: 迁移 Database Instance 领域基线

internal/database/domain/instance/instance.go

@@ -0,0 +1,101 @@
+/*
+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
+
+import "errors"
+
+// Phase is a workflow checkpoint, never evidence of external resource state.
+type Phase string
+
+const (
+	PhasePending              Phase = "Pending"
+	PhaseValidating           Phase = "Validating"
+	PhaseInitializingRegistry Phase = "InitializingRegistry"
+	PhaseReady                Phase = "Ready"
+	PhaseDeleting             Phase = "Deleting"
+)
+
+type Readiness string
+
+const (
+	Unknown  Readiness = "Unknown"
+	Ready    Readiness = "Ready"
+	NotReady Readiness = "NotReady"
+)
+
+// Snapshot contains persisted observations only, without credentials or live evidence.
+// Failure detail mapping will be added with capability assessment, not intent transitions.
+type Snapshot struct {
+	Phase            Phase
+	ObservedRevision int64
+	Readiness        Readiness
+	ReportedVersion  string
+}
+
+// Instance protects registration state and pure lifecycle transitions.
+// Reconstitution does not establish live capability evidence, even for a Ready snapshot.
+// This initial slice deliberately exposes no operation that authorizes provisioning.
+type Instance struct {
+	target   ObservationTarget
+	snapshot Snapshot
+	deleting bool
+}
+
+func Reconstitute(target ObservationTarget, snapshot Snapshot, deleting bool) (*Instance, error) {
+	if err := target.Validate(); err != nil {
+		return nil, err
+	}
+	switch snapshot.Phase {
+	case PhasePending, PhaseValidating, PhaseInitializingRegistry, PhaseReady, PhaseDeleting:
+	default:
+		snapshot.Phase = PhasePending
+		snapshot.Readiness = Unknown
+	}
+	return &Instance{target: target, snapshot: snapshot, deleting: deleting}, nil
+}
+
+func (i *Instance) Target() ObservationTarget { return i.target }
+
+// Snapshot returns a detached value. Persisting it remains the application's job.
+func (i *Instance) Snapshot() Snapshot { return i.snapshot }
+
+// BeginValidation records intent only; it does not claim a concluded observation.
+func (i *Instance) BeginValidation() error {
+	if err := i.target.Validate(); err != nil {
+		return err
+	}
+	if i.deleting {
+		return errors.New("cannot begin validation after deletion was requested")
+	}
+	i.snapshot.Phase = PhaseValidating
+	i.snapshot.Readiness = Unknown
+	return nil
+}
+
+// BeginDeletion stops the lifecycle from accepting validation. It does not delete
+// resources, inspect Tenant references, close connections or modify finalizers.
+func (i *Instance) BeginDeletion() error {
+	if err := i.target.Validate(); err != nil {
+		return err
+	}
+	if !i.deleting {
+		return errors.New("cannot begin deletion without a deletion request")
+	}
+	i.snapshot.Phase = PhaseDeleting
+	i.snapshot.Readiness = Unknown
+	return nil
+}