[management] Rework Agent Network endpoint identity and settings bootstrap (#7085)

Store the per-account gateway endpoint as {domain, proxy_address} with a
global unique index on the full hostname; dedicated = (domain ==
proxy_address). Bootstrap becomes an explicit POST carrying exactly one
of proxy_address (server allocates an adjective-noun label beneath it)
or endpoint (claimed verbatim, address-first); provider create loses its
bootstrap side effect. PUT is a full replace with every field required —
the immutable identity fields must be echoed unchanged and a mismatch is
rejected with 422. A guarded DELETE releases the endpoint: refused with
412 while providers exist or a proxy is actively serving the endpoint
hostname (matched case-insensitively); re-creating bootstraps fresh. A
self-addressed pin excludes its address from the account's cluster allow
list, and the live mapping update path now addresses the serving proxy
from the synthesized service. Existing rows are migrated on all three
store engines.

management/server/store/sql_store_agentnetwork.go

@@ -315,25 +315,65 @@ func (s *SqlStore) GetAllAgentNetworkSettings(ctx context.Context, lockStrength
 	return settings, nil
 }
 
-// GetAgentNetworkSettingsByCluster returns every Settings row pinned to
-// the given proxy cluster. Used by the bootstrap label generator to
-// build the set of subdomains already taken on a cluster.
-func (s *SqlStore) GetAgentNetworkSettingsByCluster(ctx context.Context, lockStrength LockingStrength, cluster string) ([]*agentNetworkTypes.Settings, error) {
+// GetAgentNetworkSettingsByProxyAddress returns every Settings row whose
+// gateway is served by the proxy declaring the given cluster address. Used by
+// cluster-scoped synthesis to find the accounts a shared proxy serves.
+func (s *SqlStore) GetAgentNetworkSettingsByProxyAddress(ctx context.Context, lockStrength LockingStrength, proxyAddress string) ([]*agentNetworkTypes.Settings, error) {
 	tx := s.db
 	if lockStrength != LockingStrengthNone {
 		tx = tx.Clauses(clause.Locking{Strength: string(lockStrength)})
 	}
 
 	var settings []*agentNetworkTypes.Settings
-	result := tx.Find(&settings, "cluster = ?", cluster)
+	result := tx.Find(&settings, "proxy_address = ?", proxyAddress)
 	if result.Error != nil {
-		log.WithContext(ctx).Errorf("failed to get agent network settings by cluster from store: %v", result.Error)
-		return nil, status.Errorf(status.Internal, "failed to get agent network settings by cluster from store")
+		log.WithContext(ctx).Errorf("failed to get agent network settings by proxy address from store: %v", result.Error)
+		return nil, status.Errorf(status.Internal, "failed to get agent network settings by proxy address from store")
 	}
 
 	return settings, nil
 }
 
+// GetAgentNetworkSettingsByDomain resolves the single Settings row holding the
+// given endpoint hostname — a point query on the domain unique index. Returns
+// status.NotFound when no account owns the domain.
+func (s *SqlStore) GetAgentNetworkSettingsByDomain(ctx context.Context, lockStrength LockingStrength, domain string) (*agentNetworkTypes.Settings, error) {
+	tx := s.db
+	if lockStrength != LockingStrengthNone {
+		tx = tx.Clauses(clause.Locking{Strength: string(lockStrength)})
+	}
+
+	var settings agentNetworkTypes.Settings
+	result := tx.Take(&settings, "domain = ?", domain)
+	if result.Error != nil {
+		if errors.Is(result.Error, gorm.ErrRecordNotFound) {
+			return nil, status.Errorf(status.NotFound, "agent network settings for domain %s not found", domain)
+		}
+
+		log.WithContext(ctx).Errorf("failed to get agent network settings by domain from store: %v", result.Error)
+		return nil, status.Errorf(status.Internal, "failed to get agent network settings by domain from store")
+	}
+
+	return &settings, nil
+}
+
+// CreateAgentNetworkSettings inserts a new settings row.
+//
+// Unlike SaveAgentNetworkSettings (an upsert) this is a plain INSERT, and it
+// returns the driver error unwrapped. Both properties are required by the
+// bootstrap allocator: an upsert would overwrite whichever row it collided
+// with, and the allocator classifies the rejection by matching the driver's
+// message — a unique violation on the account primary key means a concurrent
+// bootstrap for the same account won, and one on the domain index means the
+// hostname is taken.
+func (s *SqlStore) CreateAgentNetworkSettings(ctx context.Context, settings *agentNetworkTypes.Settings) error {
+	if err := s.db.Create(settings).Error; err != nil {
+		log.WithContext(ctx).Debugf("failed to create agent network settings: %v", err)
+		return err
+	}
+	return nil
+}
+
 // SaveAgentNetworkSettings upserts the per-account Agent Network
 // settings row.
 func (s *SqlStore) SaveAgentNetworkSettings(ctx context.Context, settings *agentNetworkTypes.Settings) error {
@@ -346,6 +386,25 @@ func (s *SqlStore) SaveAgentNetworkSettings(ctx context.Context, settings *agent
 	return nil
 }
 
+// DeleteAgentNetworkSettings removes the per-account Agent Network settings
+// row, releasing the account's endpoint. Returns status.NotFound when no row
+// exists. The guards on the delete (no providers, no proxy actively serving
+// the endpoint) live in the manager, which runs this inside a transaction
+// after re-checking them under a row lock.
+func (s *SqlStore) DeleteAgentNetworkSettings(ctx context.Context, accountID string) error {
+	result := s.db.Delete(&agentNetworkTypes.Settings{}, "account_id = ?", accountID)
+	if result.Error != nil {
+		log.WithContext(ctx).Errorf("failed to delete agent network settings from store: %v", result.Error)
+		return status.Errorf(status.Internal, "failed to delete agent network settings from store")
+	}
+
+	if result.RowsAffected == 0 {
+		return status.Errorf(status.NotFound, "agent network settings for account %s not found", accountID)
+	}
+
+	return nil
+}
+
 // IncrementAgentNetworkConsumption atomically upserts the consumption
 // row keyed on (account, dim_kind, dim_id, window_seconds, window_start)
 // and adds the supplied deltas. Concurrent calls from multiple proxy