diff --git a/internal/adapters/postgresadmin/adapter.go b/internal/adapters/postgresadmin/adapter.go
index 849e5d0..1d7e290 100644
--- a/internal/adapters/postgresadmin/adapter.go
+++ b/internal/adapters/postgresadmin/adapter.go
@@ -12,14 +12,14 @@ import (
 	"proxy-pool/internal/domain/adminstate"
 )
 
-var _ adminstate.Store = (*Adapter)(nil)
+var _ adminstate.Store = (*adapter)(nil)
 
 type transactionBeginner interface {
 	BeginTx(context.Context, pgx.TxOptions) (pgx.Tx, error)
 }
 
-// Adapter keeps all PostgreSQL transaction and SQL details behind adminstate.Store.
-type Adapter struct {
+// adapter keeps all PostgreSQL transaction and SQL details behind adminstate.Store.
+type adapter struct {
 	pool transactionBeginner
 }
 
@@ -28,7 +28,7 @@ func New(pool transactionBeginner) (adminstate.Store, error) {
 	if isNil(pool) {
 		return nil, adminstate.ErrInvalidCommand
 	}
-	return &Adapter{pool: pool}, nil
+	return &adapter{pool: pool}, nil
 }
 
 func isNil(value any) bool {
@@ -48,11 +48,11 @@ func contextError(ctx context.Context) error {
 	return ctx.Err()
 }
 
-func (adapter *Adapter) valid() bool {
+func (adapter *adapter) valid() bool {
 	return adapter != nil && !isNil(adapter.pool)
 }
 
-func (adapter *Adapter) begin(ctx context.Context, options pgx.TxOptions, operation string) (pgx.Tx, error) {
+func (adapter *adapter) begin(ctx context.Context, options pgx.TxOptions, operation string) (pgx.Tx, error) {
 	tx, err := adapter.pool.BeginTx(ctx, options)
 	if err != nil {
 		return nil, databaseError(ctx, operation, err)
@@ -93,8 +93,6 @@ func databaseError(ctx context.Context, operation string, err error) error {
 		switch postgresError.Code {
 		case "23505":
 			sentinel = adminstate.ErrConflict
-		case "22001", "22003", "22P02":
-			sentinel = adminstate.ErrInvalidCommand
 		}
 	}
 	return fmt.Errorf("postgresadmin: %s: %w", operation, sentinel)
diff --git a/internal/adapters/postgresadmin/adapter_external_test.go b/internal/adapters/postgresadmin/adapter_external_test.go
index eee450a..d581974 100644
--- a/internal/adapters/postgresadmin/adapter_external_test.go
+++ b/internal/adapters/postgresadmin/adapter_external_test.go
@@ -181,6 +181,14 @@ func TestDatabaseErrorsAreMappedAndRedacted(t *testing.T) {
 			},
 			want: adminstate.ErrUnavailable,
 		},
+		{
+			name: "value too long",
+			err: &pgconn.PgError{
+				Code:    "22001",
+				Message: "backend encoding failed with secret details",
+			},
+			want: adminstate.ErrUnavailable,
+		},
 	}
 	for _, test := range tests {
 		test := test
diff --git a/internal/adapters/postgresadmin/mutate.go b/internal/adapters/postgresadmin/mutate.go
index 6bd94dd..26a3578 100644
--- a/internal/adapters/postgresadmin/mutate.go
+++ b/internal/adapters/postgresadmin/mutate.go
@@ -30,7 +30,7 @@ const (
 		) VALUES ($1, $2, $3, $4, $5, $6)`
 )
 
-func (adapter *Adapter) CommitConfig(
+func (adapter *adapter) CommitConfig(
 	ctx context.Context,
 	command adminstate.CommitConfigCommand,
 ) (adminstate.MutationResult, error) {
@@ -125,7 +125,7 @@ func (adapter *Adapter) CommitConfig(
 	}, nil
 }
 
-func (adapter *Adapter) SetUpstreamEnabled(
+func (adapter *adapter) SetUpstreamEnabled(
 	ctx context.Context,
 	command adminstate.SetUpstreamCommand,
 ) (adminstate.MutationResult, error) {
@@ -208,7 +208,7 @@ func (adapter *Adapter) SetUpstreamEnabled(
 	}, nil
 }
 
-func (adapter *Adapter) SwitchRouting(
+func (adapter *adapter) SwitchRouting(
 	ctx context.Context,
 	command adminstate.SwitchRoutingCommand,
 ) (adminstate.MutationResult, error) {
@@ -301,7 +301,7 @@ func (adapter *Adapter) SwitchRouting(
 	}, nil
 }
 
-func (adapter *Adapter) beginMutation(ctx context.Context, operation string) (pgx.Tx, int64, error) {
+func (adapter *adapter) beginMutation(ctx context.Context, operation string) (pgx.Tx, int64, error) {
 	tx, err := adapter.begin(ctx, pgx.TxOptions{AccessMode: pgx.ReadWrite}, operation)
 	if err != nil {
 		return nil, 0, err
diff --git a/internal/adapters/postgresadmin/outbox.go b/internal/adapters/postgresadmin/outbox.go
index c50b10d..5587187 100644
--- a/internal/adapters/postgresadmin/outbox.go
+++ b/internal/adapters/postgresadmin/outbox.go
@@ -10,7 +10,7 @@ import (
 	"proxy-pool/internal/domain/adminstate"
 )
 
-func (adapter *Adapter) Claim(
+func (adapter *adapter) Claim(
 	ctx context.Context,
 	command adminstate.ClaimCommand,
 ) ([]adminstate.Event, error) {
@@ -106,7 +106,7 @@ func (adapter *Adapter) Claim(
 	return events, nil
 }
 
-func (adapter *Adapter) Acknowledge(
+func (adapter *adapter) Acknowledge(
 	ctx context.Context,
 	command adminstate.AcknowledgeCommand,
 ) error {
diff --git a/internal/adapters/postgresadmin/snapshot.go b/internal/adapters/postgresadmin/snapshot.go
index f7daae4..7901060 100644
--- a/internal/adapters/postgresadmin/snapshot.go
+++ b/internal/adapters/postgresadmin/snapshot.go
@@ -9,7 +9,7 @@ import (
 	"proxy-pool/internal/domain/adminstate"
 )
 
-func (adapter *Adapter) Snapshot(ctx context.Context) (adminstate.Snapshot, error) {
+func (adapter *adapter) Snapshot(ctx context.Context) (adminstate.Snapshot, error) {
 	if err := contextError(ctx); err != nil {
 		return adminstate.Snapshot{}, err
 	}
@@ -78,7 +78,7 @@ func (adapter *Adapter) Snapshot(ctx context.Context) (adminstate.Snapshot, erro
 	return snapshot, nil
 }
 
-func (adapter *Adapter) ReadAudit(
+func (adapter *adapter) ReadAudit(
 	ctx context.Context,
 	query adminstate.AuditQuery,
 ) ([]adminstate.AuditRecord, error) {