diff --git a/internal/app/state/data.go b/internal/app/state/data.go
new file mode 100644
index 0000000..3c289f9
--- /dev/null
+++ b/internal/app/state/data.go
@@ -0,0 +1,43 @@
+package state
+
+import (
+	"encoding/gob"
+	"fmt"
+	"io"
+	"os"
+
+	"hakurei.app/hst"
+)
+
+// entryEncode encodes [hst.State] into [io.Writer] with the state entry header.
+// entryEncode does not validate the embedded [hst.Config] value.
+//
+// A non-nil error returned by entryEncode is of type [hst.AppError].
+func entryEncode(w io.Writer, s *hst.State) error {
+	if err := entryWriteHeader(w, s.Enablements.Unwrap()); err != nil {
+		return &hst.AppError{Step: "encode state header", Err: err}
+	} else if err = gob.NewEncoder(w).Encode(s); err != nil {
+		return &hst.AppError{Step: "encode state body", Err: err}
+	} else {
+		return nil
+	}
+}
+
+// entryDecode decodes [hst.State] from [io.Reader] and stores the result in the value pointed to by p.
+// entryDecode validates the embedded [hst.Config] value.
+//
+// A non-nil error returned by entryDecode is of type [hst.AppError].
+func entryDecode(r io.Reader, p *hst.State) error {
+	if et, err := entryReadHeader(r); err != nil {
+		return &hst.AppError{Step: "decode state header", Err: err}
+	} else if err = gob.NewDecoder(r).Decode(&p); err != nil {
+		return &hst.AppError{Step: "decode state body", Err: err}
+	} else if err = p.Config.Validate(); err != nil {
+		return err
+	} else if p.Enablements.Unwrap() != et {
+		return &hst.AppError{Step: "validate state enablement", Err: os.ErrInvalid,
+			Msg: fmt.Sprintf("state entry %s has unexpected enablement byte %#x, %#x", p.ID.String(), byte(p.Enablements.Unwrap()), byte(et))}
+	} else {
+		return nil
+	}
+}
diff --git a/internal/app/state/data_test.go b/internal/app/state/data_test.go
new file mode 100644
index 0000000..49f0f52
--- /dev/null
+++ b/internal/app/state/data_test.go
@@ -0,0 +1,139 @@
+package state
+
+import (
+	"bytes"
+	"encoding/gob"
+	"errors"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+
+	"hakurei.app/container/stub"
+	"hakurei.app/hst"
+)
+
+func TestEntryData(t *testing.T) {
+	t.Parallel()
+	newTemplateState := func() *hst.State {
+		return &hst.State{
+			ID:      hst.ID(bytes.Repeat([]byte{0xaa}, len(hst.ID{}))),
+			PID:     0xcafebabe,
+			ShimPID: 0xdeadbeef,
+			Config:  hst.Template(),
+			Time:    time.Unix(0, 0),
+		}
+	}
+
+	mustEncodeGob := func(e any) string {
+		var buf bytes.Buffer
+		if err := gob.NewEncoder(&buf).Encode(e); err != nil {
+			t.Fatalf("cannot encode invalid state: %v", err)
+			return "\x00" // not reached
+		} else {
+			return buf.String()
+		}
+	}
+	templateStateGob := mustEncodeGob(newTemplateState())
+
+	testCases := []struct {
+		name string
+		data string
+		s    *hst.State
+		err  error
+	}{
+		{"invalid header", "\x00\xff\xca\xfe\xff\xff\xff\x00", nil, &hst.AppError{
+			Step: "decode state header", Err: errors.New("unexpected revision ffff")}},
+
+		{"invalid gob", "\x00\xff\xca\xfe\x00\x00\xff\x00", nil, &hst.AppError{
+			Step: "decode state body", Err: io.EOF}},
+
+		{"invalid config", "\x00\xff\xca\xfe\x00\x00\xff\x00" + mustEncodeGob(new(hst.State)), new(hst.State), &hst.AppError{
+			Step: "validate configuration", Err: hst.ErrConfigNull,
+			Msg: "invalid configuration"}},
+
+		{"inconsistent enablement", "\x00\xff\xca\xfe\x00\x00\xff\x00" + templateStateGob, newTemplateState(), &hst.AppError{
+			Step: "validate state enablement", Err: os.ErrInvalid,
+			Msg: "state entry aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa has unexpected enablement byte 0xd, 0xff"}},
+
+		{"template", "\x00\xff\xca\xfe\x00\x00\x0d\xf2" + templateStateGob, newTemplateState(), nil},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			t.Run("encode", func(t *testing.T) {
+				if tc.s == nil || tc.s.Config == nil {
+					return
+				}
+				t.Parallel()
+
+				var buf bytes.Buffer
+				if err := entryEncode(&buf, tc.s); err != nil {
+					t.Fatalf("entryEncode: error = %v", err)
+				}
+
+				if tc.err == nil {
+					// Gob encoding is not guaranteed to be deterministic.
+					// While the current implementation mostly is, it has randomised order
+					// for iterating over maps, and hst.Config holds a map for environ.
+					var got hst.State
+					if err := entryDecode(&buf, &got); err != nil {
+						t.Fatalf("entryDecode: error = %v", err)
+					}
+					if !reflect.DeepEqual(&got, tc.s) {
+						t.Errorf("entryEncode: %x", buf.Bytes())
+					}
+				} else if testing.Verbose() {
+					t.Logf("%x", buf.String())
+				}
+			})
+
+			t.Run("decode", func(t *testing.T) {
+				t.Parallel()
+
+				var got hst.State
+				if err := entryDecode(strings.NewReader(tc.data), &got); !reflect.DeepEqual(err, tc.err) {
+					t.Fatalf("entryDecode: error = %#v, want %#v", err, tc.err)
+				} else if err != nil {
+					return
+				}
+
+				if !reflect.DeepEqual(&got, tc.s) {
+					t.Errorf("entryDecode: %#v, want %#v", &got, tc.s)
+				}
+			})
+		})
+	}
+
+	t.Run("encode fault", func(t *testing.T) {
+		t.Parallel()
+		s := newTemplateState()
+
+		t.Run("gob", func(t *testing.T) {
+			var want = &hst.AppError{Step: "encode state body", Err: stub.UniqueError(0xcafe)}
+			if err := entryEncode(stubNErrorWriter(entryHeaderSize), s); !reflect.DeepEqual(err, want) {
+				t.Errorf("entryEncode: error = %#v, want %#v", err, want)
+			}
+		})
+
+		t.Run("header", func(t *testing.T) {
+			var want = &hst.AppError{Step: "encode state header", Err: stub.UniqueError(0xcafe)}
+			if err := entryEncode(stubNErrorWriter(entryHeaderSize-1), s); !reflect.DeepEqual(err, want) {
+				t.Errorf("entryEncode: error = %#v, want %#v", err, want)
+			}
+		})
+	})
+}
+
+// stubNErrorWriter returns an error for writes above a certain size.
+type stubNErrorWriter int
+
+func (w stubNErrorWriter) Write(p []byte) (n int, err error) {
+	if len(p) > int(w) {
+		return int(w), stub.UniqueError(0xcafe)
+	}
+	return io.Discard.Write(p)
+}
diff --git a/internal/app/state/multi.go b/internal/app/state/multi.go
index 695bff1..446d6ce 100644
--- a/internal/app/state/multi.go
+++ b/internal/app/state/multi.go
@@ -1,7 +1,6 @@
 package state
 
 import (
-	"encoding/gob"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -161,25 +160,18 @@ func (b *multiBackend) load(decode bool) (map[hst.ID]*hst.State, error) {
 
 				// append regardless, but only parse if required, implements Len
 				if decode {
-					var et hst.Enablement
-					if et, err = entryReadHeader(f); err != nil {
+					if err = entryDecode(f, &s); err != nil {
 						_ = f.Close()
-						return &hst.AppError{Step: "decode state header", Err: err}
-					} else if err = gob.NewDecoder(f).Decode(&s); err != nil {
-						_ = f.Close()
-						return &hst.AppError{Step: "decode state body", Err: err}
-					} else if s.ID != id {
-						_ = f.Close()
-						return fmt.Errorf("state entry %s has unexpected id %s", id, &s.ID)
-					} else if err = f.Close(); err != nil {
-						return &hst.AppError{Step: "close state file", Err: err}
-					} else if err = s.Config.Validate(); err != nil {
 						return err
-					} else if s.Enablements.Unwrap() != et {
-						return fmt.Errorf("state entry %s has unexpected enablement byte %x, %x", id, s.Enablements, et)
+					} else if s.ID != id {
+						return &hst.AppError{Step: "validate state identifier", Err: os.ErrInvalid,
+							Msg: fmt.Sprintf("state entry %s has unexpected id %s", id, &s.ID)}
 					}
 				}
 
+				if err = f.Close(); err != nil {
+					return &hst.AppError{Step: "close state file", Err: err}
+				}
 				return nil
 			}
 		}(); err != nil {
@@ -202,12 +194,9 @@ func (b *multiBackend) Save(state *hst.State) error {
 	statePath := b.filename(&state.ID)
 	if f, err := os.OpenFile(statePath, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600); err != nil {
 		return &hst.AppError{Step: "create state file", Err: err}
-	} else if err = entryWriteHeader(f, state.Enablements.Unwrap()); err != nil {
+	} else if err = entryEncode(f, state); err != nil {
 		_ = f.Close()
-		return &hst.AppError{Step: "encode state header", Err: err}
-	} else if err = gob.NewEncoder(f).Encode(state); err != nil {
-		_ = f.Close()
-		return &hst.AppError{Step: "encode state body", Err: err}
+		return err
 	} else if err = f.Close(); err != nil {
 		return &hst.AppError{Step: "close state file", Err: err}
 	}