fix(model): tighten Config.ParentKey fallback to variables configs only

- Require both ErrMultipleParents AND ComponentID == keboola.VariablesComponentID
  before falling back to branch parent, so schedulers and other component
  types with unexpected multi-parent errors are never silently swallowed
- Remove inaccurate claim that VariablesForRelation is only constructed by
  NewOtherSideRelation; the comment now simply states the invariant
- Add TestConfig_ParentKey_MultipleParentsFallsBackToBranch to cover the
  shared-variables fallback path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Matovidlo

internal/pkg/model/object.go

@@ -595,19 +595,17 @@ func (r *ConfigRow) GetContent() *orderedmap.OrderedMap {
 }
 
 // ParentKey - config parent can be modified via Relations, e.g. variables config embedded in another config.
-// When Relations.ParentKey returns ErrMultipleParents (a shared variables config), fall back to the
-// structural parent (branch). VariablesForRelation is only ever constructed by
-// VariablesFromRelation.NewOtherSideRelation, which hard-codes ComponentID: keboola.VariablesComponentID,
-// so neither checkDefinedOn guard can trigger in practice. All other errors are propagated.
+// When a keboola.variables config is shared by multiple consumers (ErrMultipleParents), fall back to the
+// structural parent (branch). All other errors are propagated.
 func (c *Config) ParentKey() (Key, error) {
 	parentKey, err := c.Relations.ParentKey(c.Key())
 	if err == nil && parentKey != nil {
 		return parentKey, nil
 	}
-	if err != nil && !errors.Is(err, ErrMultipleParents) {
+	if err != nil && (!errors.Is(err, ErrMultipleParents) || c.ComponentID != keboola.VariablesComponentID) {
 		return nil, err
 	}
-	// No relation-defined parent, or multiple parents (shared variables config) —
+	// No relation-defined parent, or shared variables config with multiple consumers —
 	// fall back to the structural parent (branch).
 	return c.ConfigKey.ParentKey()
 }

internal/pkg/model/object_test.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/keboola/go-utils/pkg/wildcards"
+	"github.com/keboola/keboola-sdk-go/v2/pkg/keboola"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -94,6 +95,20 @@ func TestBranchMetadata_UpsertTemplateInstance_New(t *testing.T) {
 	}, usages)
 }
 
+func TestConfig_ParentKey_MultipleParentsFallsBackToBranch(t *testing.T) {
+	t.Parallel()
+	cfg := &Config{
+		ConfigKey: ConfigKey{BranchID: 1, ComponentID: keboola.VariablesComponentID, ID: "3"},
+		Relations: Relations{
+			&VariablesForRelation{ComponentID: "ex-generic-v2", ConfigID: "1"},
+			&VariablesForRelation{ComponentID: "ex-generic-v2", ConfigID: "2"},
+		},
+	}
+	parentKey, err := cfg.ParentKey()
+	require.NoError(t, err)
+	assert.Equal(t, BranchKey{ID: 1}, parentKey)
+}
+
 func TestBranchMetadata_DeleteTemplateUsage(t *testing.T) {
 	t.Parallel()