fix: harden target recovery metadata safety

internal/shell/shell_test.go

@@ -77,6 +77,43 @@ func TestShellAdapterRunsReusableTargetContract(t *testing.T) {
 	}
 }
 
+func TestIncompleteRecoveryMetadataRejectsRestoreWithoutChangingShellConfiguration(t *testing.T) {
+	fingerprint := strings.Repeat("a", 64)
+	cases := map[string]string{
+		"empty object":          `{}`,
+		"missing restoration":   `{"version":1,"fingerprint":"` + fingerprint + `","original":null}`,
+		"invalid fingerprint":   `{"version":1,"fingerprint":"short","original":{}}`,
+		"conflicting originals": `{"version":1,"fingerprint":"` + fingerprint + `","original":{"HTTP_PROXY":"http://prior.example:3128"},"originalScript":"export HTTP_PROXY=http://prior.example:3128\\n"}`,
+	}
+	for name, metadata := range cases {
+		t.Run(name, func(t *testing.T) {
+			a := newAdapter(t, "/bin/bash", nil)
+			environment := []byte("export HTTP_PROXY='http://managed.example:8080'\n")
+			for path, data := range map[string][]byte{a.EnvironmentPath(): environment, a.RecoveryPath(): []byte(metadata)} {
+				if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(path, data, 0o600); err != nil {
+					t.Fatal(err)
+				}
+			}
+			if inspection := a.Inspect(context.Background(), nil); inspection.State != target.Drifted {
+				t.Fatalf("inspection = %#v", inspection)
+			}
+			result := a.SetDesired(context.Background(), false, nil)
+			if result.Err == nil || result.Inspection.State != target.Drifted {
+				t.Fatalf("unsafe disable = %#v", result)
+			}
+			if got := readFile(t, a.EnvironmentPath()); got != string(environment) {
+				t.Fatalf("environment changed to %q", got)
+			}
+			if got := readFile(t, a.RecoveryPath()); got != metadata {
+				t.Fatalf("recovery changed to %q", got)
+			}
+		})
+	}
+}
+
 func TestRecoveryFailureRetryPreservesOriginalShellState(t *testing.T) {
 	files := &failingFS{FileSystem: shell.OSFileSystem{}, failRecoveryOnce: true}
 	a := newAdapterWithFS(t, "/bin/bash", map[string]string{"HTTP_PROXY": "http://prior.example:3128"}, files)