Add DirectSourceFetch feature gate to bypass cache for source objects

This feature gate enables fetching source objects (GitRepository,
OCIRepository, Bucket) directly from the API server using APIReader,
bypassing the controller's cache. This can be useful when immediate
consistency is required for source object reads.

When enabled via --feature-gates=DirectSourceFetch=true:
- Source objects are fetched using r.APIReader instead of r.Client
- A log message is emitted at startup indicating the feature is active

Changes:
- Add DirectSourceFetch field to KustomizationReconciler struct
- Update getSource() to use APIReader when feature is enabled
- Register feature gate with default value false (opt-in)
- Add unit tests for GitRepository, OCIRepository, and Bucket sources
- Update pkg/runtime dependency to v0.100.1
- Downgrade pkg/ssa to v0.67.1

Signed-off-by: Dipti Pai <diptipai89@outlook.com>

Author: dipti-pai

go.mod

@@ -28,8 +28,8 @@ require (
 	github.com/fluxcd/pkg/cache v0.13.0
 	github.com/fluxcd/pkg/http/fetch v0.22.0
 	github.com/fluxcd/pkg/kustomize v1.27.0
-	github.com/fluxcd/pkg/runtime v0.100.0
-	github.com/fluxcd/pkg/ssa v0.68.0
+	github.com/fluxcd/pkg/runtime v0.100.1
+	github.com/fluxcd/pkg/ssa v0.67.1
 	github.com/fluxcd/pkg/tar v0.17.0
 	github.com/fluxcd/pkg/testserver v0.13.0
 	github.com/fluxcd/source-controller/api v1.7.2

go.sum

@@ -210,12 +210,12 @@ github.com/fluxcd/pkg/http/fetch v0.22.0 h1:FT8CfstPE/e7+KRxNrx8ZJ1Uj5rkR5wXOtvQ
 github.com/fluxcd/pkg/http/fetch v0.22.0/go.mod h1:X+8wF3peP79TyyDSgCJiavz+fAcYaf7CRXSeu7ccsPA=
 github.com/fluxcd/pkg/kustomize v1.27.0 h1:bWoWVaHV1ZRo3Ei1JXpY58hJK25WWna+az5jj6zseE0=
 github.com/fluxcd/pkg/kustomize v1.27.0/go.mod h1:KKb26vz5EApyOrgencDlvixJnuI6cnkWGks95sK9AFs=
-github.com/fluxcd/pkg/runtime v0.100.0 h1:7k2T/zlOLZ+knVr5fGB6cqq3Dr9D1k2jEe6AJo91JlI=
-github.com/fluxcd/pkg/runtime v0.100.0/go.mod h1:SctSsHvFwUfiOVP1zirP6mo7I8wQtXeWVl2lNQWal88=
+github.com/fluxcd/pkg/runtime v0.100.1 h1:UiPmgY8Yv7UF06MT5T8AG9uDGNszm75/DQtK6JEhnrM=
+github.com/fluxcd/pkg/runtime v0.100.1/go.mod h1:SctSsHvFwUfiOVP1zirP6mo7I8wQtXeWVl2lNQWal88=
 github.com/fluxcd/pkg/sourceignore v0.17.0 h1:Z72nruRMhC15zIEpWoDrAcJcJ1El6QDnP/aRDfE4WOA=
 github.com/fluxcd/pkg/sourceignore v0.17.0/go.mod h1:3e/VmYLId0pI/H5sK7W9Ibif+j0Ahns9RxNjDMtTTfY=
-github.com/fluxcd/pkg/ssa v0.68.0 h1:hdRFrBJO9dh04200tNJljpi4TOArHC0nq+LUFZxMgKc=
-github.com/fluxcd/pkg/ssa v0.68.0/go.mod h1:PFXVjChubQOiWDxalpwh6PzRsEswGqnKwZB4ScoxDx4=
+github.com/fluxcd/pkg/ssa v0.67.1 h1:wmwrznP+USRUtppKRjAiBx3ayriygRx0IeMdX7z/HaM=
+github.com/fluxcd/pkg/ssa v0.67.1/go.mod h1:PFXVjChubQOiWDxalpwh6PzRsEswGqnKwZB4ScoxDx4=
 github.com/fluxcd/pkg/tar v0.17.0 h1:uNxbFXy8ly8C7fJ8D7w3rjTNJFrb4Hp1aY/30XkfvxY=
 github.com/fluxcd/pkg/tar v0.17.0/go.mod h1:b1xyIRYDD0ket4SV5u0UXYv+ZdN/O/HmIO5jZQdHQls=
 github.com/fluxcd/pkg/testserver v0.13.0 h1:xEpBcEYtD7bwvZ+i0ZmChxKkDo/wfQEV3xmnzVybSSg=

internal/controller/kustomization_controller.go

@@ -70,7 +70,6 @@ import (
 
 	kustomizev1 "github.com/fluxcd/kustomize-controller/api/v1"
 	"github.com/fluxcd/kustomize-controller/internal/decryptor"
-	"github.com/fluxcd/kustomize-controller/internal/features"
 	"github.com/fluxcd/kustomize-controller/internal/inventory"
 )
 
@@ -118,6 +117,7 @@ type KustomizationReconciler struct {
 
 	AdditiveCELDependencyCheck bool
 	AllowExternalArtifact      bool
+	DirectSourceFetch          bool
 	FailFast                   bool
 	GroupChangeLog             bool
 	StrictSubstitutions        bool
@@ -686,13 +686,19 @@ func (r *KustomizationReconciler) getSource(ctx context.Context,
 	if obj.Spec.SourceRef.Kind == sourcev1.ExternalArtifactKind && !r.AllowExternalArtifact {
 		return src, acl.AccessDeniedError(
 			fmt.Sprintf("can't access '%s/%s', %s feature gate is disabled",
-				obj.Spec.SourceRef.Kind, namespacedName, features.ExternalArtifact))
+				obj.Spec.SourceRef.Kind, namespacedName, runtimeCtrl.FeatureGateExternalArtifact))
+	}
+
+	// Use APIReader to bypass the cache when DirectSourceFetch is enabled.
+	var reader client.Reader = r.Client
+	if r.DirectSourceFetch {
+		reader = r.APIReader
 	}
 
 	switch obj.Spec.SourceRef.Kind {
 	case sourcev1.OCIRepositoryKind:
 		var repository sourcev1.OCIRepository
-		err := r.Client.Get(ctx, namespacedName, &repository)
+		err := reader.Get(ctx, namespacedName, &repository)
 		if err != nil {
 			if apierrors.IsNotFound(err) {
 				return src, err
@@ -702,7 +708,7 @@ func (r *KustomizationReconciler) getSource(ctx context.Context,
 		src = &repository
 	case sourcev1.GitRepositoryKind:
 		var repository sourcev1.GitRepository
-		err := r.Client.Get(ctx, namespacedName, &repository)
+		err := reader.Get(ctx, namespacedName, &repository)
 		if err != nil {
 			if apierrors.IsNotFound(err) {
 				return src, err
@@ -712,7 +718,7 @@ func (r *KustomizationReconciler) getSource(ctx context.Context,
 		src = &repository
 	case sourcev1.BucketKind:
 		var bucket sourcev1.Bucket
-		err := r.Client.Get(ctx, namespacedName, &bucket)
+		err := reader.Get(ctx, namespacedName, &bucket)
 		if err != nil {
 			if apierrors.IsNotFound(err) {
 				return src, err
@@ -722,7 +728,7 @@ func (r *KustomizationReconciler) getSource(ctx context.Context,
 		src = &bucket
 	case sourcev1.ExternalArtifactKind:
 		var ea sourcev1.ExternalArtifact
-		err := r.Client.Get(ctx, namespacedName, &ea)
+		err := reader.Get(ctx, namespacedName, &ea)
 		if err != nil {
 			if apierrors.IsNotFound(err) {
 				return src, err