Return a higher-level error when state is invalid

coroutine.go

@@ -104,6 +104,12 @@ func LoadContext[R, S any]() *Context[R, S] {
 	}
 }
 
-// ErrNotDurable is an error that occurs when attempting to
-// serialize a coroutine that is not durable.
-var ErrNotDurable = errors.New("only durable coroutines can be serialized")
+var (
+	// ErrNotDurable is an error that occurs when attempting to
+	// serialize a coroutine that is not durable.
+	ErrNotDurable = errors.New("only durable coroutines can be serialized")
+
+	// ErrInvalidState is an error that occurs when attempting to
+	// deserialize a coroutine that was serialized in another build.
+	ErrInvalidState = errors.New("durable coroutine was serialized in another build")
+)

coroutine_durable.go

@@ -3,6 +3,7 @@
 package coroutine
 
 import (
+	"errors"
 	"runtime"
 	"unsafe"
 
@@ -95,6 +96,9 @@ func (c *Context[R, S]) Unmarshal(b []byte) (int, error) {
 	start := len(b)
 	v, b, err := types.Deserialize(b)
 	if err != nil {
+		if errors.Is(err, types.ErrBuildIDMismatch) {
+			return 0, ErrInvalidState
+		}
 		return 0, err
 	}
 	s := v.(*serializedCoroutine)