feat: typed decode and encode errors with the key path

Assisted-by: GLM 5.3 Flash

decode.go

@@ -117,20 +117,20 @@ func (d *decoder) assignStruct(tbl map[string]any, dst reflect.Value) error {
 				// of the encoder inlining that map's entries.
 				mv, err := fieldByIndex(dst, schema.embedMaps[0])
 				if err != nil {
-					return fmt.Errorf("%s: %w", key, err)
+					return newDecodeError(key, err)
 				}
 				if err := d.assignMap(map[string]any{key: val}, mv); err != nil {
-					return fmt.Errorf("%s: %w", key, err)
+					return newDecodeError(key, err)
 				}
 			}
 			continue
 		}
 		fv, err := fieldByIndex(dst, field.index)
 		if err != nil {
-			return fmt.Errorf("%s: %w", key, err)
+			return newDecodeError(key, err)
 		}
 		if err := d.assign(val, fv); err != nil {
-			return fmt.Errorf("%s: %w", key, err)
+			return newDecodeError(key, err)
 		}
 	}
 	return nil
@@ -147,7 +147,7 @@ func (d *decoder) assignMap(tbl map[string]any, dst reflect.Value) error {
 	for key, val := range tbl {
 		elem := reflect.New(elemType).Elem()
 		if err := d.assign(val, elem); err != nil {
-			return fmt.Errorf("%s: %w", key, err)
+			return newDecodeError(key, err)
 		}
 		dst.SetMapIndex(reflect.ValueOf(key), elem)
 	}
@@ -161,7 +161,7 @@ func (d *decoder) assignSlice(items []any, dst reflect.Value) error {
 	out := reflect.MakeSlice(dst.Type(), len(items), len(items))
 	for i, item := range items {
 		if err := d.assign(item, out.Index(i)); err != nil {
-			return fmt.Errorf("[%d]: %w", i, err)
+			return newDecodeError(fmt.Sprintf("[%d]", i), err)
 		}
 	}
 	dst.Set(out)
@@ -175,7 +175,7 @@ func (d *decoder) assignTableSlice(items []map[string]any, dst reflect.Value) er
 	out := reflect.MakeSlice(dst.Type(), len(items), len(items))
 	for i, item := range items {
 		if err := d.assign(item, out.Index(i)); err != nil {
-			return fmt.Errorf("[%d]: %w", i, err)
+			return newDecodeError(fmt.Sprintf("[%d]", i), err)
 		}
 	}
 	dst.Set(out)