diff --git a/core/pkg/evaluator/fractional.go b/core/pkg/evaluator/fractional.go
index 0163e0929..5d3973789 100644
--- a/core/pkg/evaluator/fractional.go
+++ b/core/pkg/evaluator/fractional.go
@@ -61,7 +61,7 @@ func parseFractionalEvaluationData(values, data any, logger *logger.Logger) (str
 	if !ok {
 		return "", nil, errors.New("fractional evaluation data is not an array")
 	}
-if len(valuesArray) < 1 {
+	if len(valuesArray) < 1 {
 		return "", nil, errors.New("fractional evaluation data must contain at least one distribution")
 	}
 
@@ -195,7 +195,7 @@ func parseFractionalEvaluationDistributions(values []any, data any, logger *logg
 // It maps a 32-bit hash to the range [0, totalWeight) and finds the variant bucket that contains that value.
 func distributeValue(hashValue uint32, feDistribution *fractionalEvaluationDistribution) any {
 	if feDistribution.totalWeight == 0 {
-		return ""
+		return nil
 	}
 
 	bucket := (uint64(hashValue) * uint64(feDistribution.totalWeight)) >> 32
@@ -209,5 +209,5 @@ func distributeValue(hashValue uint32, feDistribution *fractionalEvaluationDistr
 	}
 
 	// unreachable given validation
-	return ""
+	return nil
 }
diff --git a/core/pkg/evaluator/fractional_test.go b/core/pkg/evaluator/fractional_test.go
index 6fcfa7ffb..789a626d4 100644
--- a/core/pkg/evaluator/fractional_test.go
+++ b/core/pkg/evaluator/fractional_test.go
@@ -1073,3 +1073,57 @@ func TestFractionalVariantBoolNumericAndOperators(t *testing.T) {
 		})
 	}
 }
+
+func TestFractionalEvaluation_ErrorFallbackWhenUsedDirectly(t *testing.T) {
+	const source = "testSource"
+	ctx := context.Background()
+
+	tests := map[string]struct {
+		targeting string
+		context   map[string]any
+	}{
+		"missing bucket key falls back": {
+			targeting: `{
+				"fractional": [
+					{"var": "missing_key"},
+					["one", 50],
+					["two", 50]
+				]
+			}`,
+			context: map[string]any{},
+		},
+		"all zero weights fall back": {
+			targeting: `{
+				"fractional": [
+					{"var": "targetingKey"},
+					["one", 0],
+					["two", 0]
+				]
+			}`,
+			context: map[string]any{"targetingKey": "any-user"},
+		},
+	}
+
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			je, err := setupEvaluator(source, []model.Flag{{
+				Key:            "fractional-op-error-fallback",
+				State:          "ENABLED",
+				DefaultVariant: "fallback",
+				Variants: map[string]any{
+					"one":      "one",
+					"two":      "two",
+					"fallback": "fallback",
+				},
+				Targeting: []byte(tt.targeting),
+			}})
+			assert.NoError(t, err)
+
+			value, variant, reason, _, err := resolve[string](ctx, "default", "fractional-op-error-fallback", tt.context, je.evaluateVariant)
+			assert.NoError(t, err)
+			assert.Equal(t, "fallback", value)
+			assert.Equal(t, "fallback", variant)
+			assert.Equal(t, model.DefaultReason, reason)
+		})
+	}
+}
diff --git a/core/pkg/evaluator/json.go b/core/pkg/evaluator/json.go
index 428ff35c8..bb3cdc223 100644
--- a/core/pkg/evaluator/json.go
+++ b/core/pkg/evaluator/json.go
@@ -6,7 +6,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"regexp"
 	"strings"
 	"time"
 
@@ -35,12 +34,6 @@ const (
 	ProtoVersionKey = "__flagd.protoVersion__" // used to mark if the request is coming from an older proto source, which has different fallback behavior
 )
 
-var regBrace *regexp.Regexp
-
-func init() {
-	regBrace = regexp.MustCompile("^[^{]*{|}[^}]*$")
-}
-
 func addSchemaResource(compiler *jsonschema.Compiler, url string, schemaData string) error {
 	unmarshalJSON, err := jsonschema.UnmarshalJSON(strings.NewReader(schemaData))
 	if err != nil {
@@ -548,13 +541,18 @@ func transposeEvaluators(state string) (string, error) {
 		return "", fmt.Errorf("unmarshal: %w", err)
 	}
 
-	for evalName, evalRaw := range evaluators.Evaluators {
-		// replace any occurrences of "evaluator": "evalName"
-		regex, err := regexp.Compile(fmt.Sprintf(`"\$ref":(\s)*"%s"`, evalName))
-		if err != nil {
-			return "", fmt.Errorf("compile regex: %w", err)
-		}
+	// round-trip to normalize whitespace so we can use plain string matching
+	var raw interface{}
+	if err := json.Unmarshal([]byte(state), &raw); err != nil {
+		return "", fmt.Errorf("normalize: %w", err)
+	}
+	normalizedBytes, err := json.Marshal(raw)
+	if err != nil {
+		return "", fmt.Errorf("normalize marshal: %w", err)
+	}
+	result := string(normalizedBytes)
 
+	for evalName, evalRaw := range evaluators.Evaluators {
 		marshalledEval, err := evalRaw.MarshalJSON()
 		if err != nil {
 			return "", fmt.Errorf("marshal evaluator: %w", err)
@@ -564,9 +562,10 @@ func transposeEvaluators(state string) (string, error) {
 		if len(evalValue) < 3 {
 			return "", errors.New("evaluator object is empty")
 		}
-		evalValue = regBrace.ReplaceAllString(evalValue, "")
-		state = regex.ReplaceAllString(state, evalValue)
+
+		refPattern := `{"$ref":"` + evalName + `"}`
+		result = strings.ReplaceAll(result, refPattern, evalValue)
 	}
 
-	return state, nil
+	return result, nil
 }
diff --git a/core/pkg/evaluator/json_test.go b/core/pkg/evaluator/json_test.go
index d9b988692..14993f0e0 100644
--- a/core/pkg/evaluator/json_test.go
+++ b/core/pkg/evaluator/json_test.go
@@ -1145,37 +1145,56 @@ func TestState_Evaluator(t *testing.T) {
 				},
 			},
 		},
-		"invalid evaluator json": {
+		"string-valued evaluator": {
+			// string-valued evaluators are valid; the string is substituted as-is (with quotes)
 			inputState: `
 				{
   					"flags": {
-						"fibAlgo": {
-						  "variants": {
-							"recursive": "recursive",
-							"memo": "memo",
-							"loop": "loop",
-							"binet": "binet"
-						  },
-						  "defaultVariant": "recursive",
-						  "state": "ENABLED",
-						  "metadata": {
-						    "flagSetId": "flagSetId"
-						  },
-						  "targeting": {
-							"if": [
-							  {
-								"$ref": "emailWithFaas"
-							  }, "binet", null
-							]
-						  }
-    					}
+					"fibAlgo": {
+					  "variants": {
+						"recursive": "recursive",
+						"memo": "memo",
+						"loop": "loop",
+						"binet": "binet"
+					  },
+					  "defaultVariant": "recursive",
+					  "state": "ENABLED",
+					  "metadata": {
+					    "flagSetId": "flagSetId"
+					  },
+					  "targeting": {
+						"if": [
+						  {
+							"$ref": "emailWithFaas"
+						  }, "binet", null
+						]
+					  }
+    				}
+				},
+				"$evaluators": {
+					"emailWithFaas": "foo"
+  				}
+			}
+		`,
+			expectedOutputState: map[string]model.Flag{
+				"fibAlgo": {
+					Key: "fibAlgo",
+					Variants: map[string]any{
+						"recursive": "recursive",
+						"memo":      "memo",
+						"loop":      "loop",
+						"binet":     "binet",
 					},
-					"$evaluators": {
-						"emailWithFaas": "foo"
-  					}
-				}
-			`,
-			expectedError: true,
+					DefaultVariant: "recursive",
+					State:          "ENABLED",
+					Source:         "testSource",
+					Targeting:      json.RawMessage(`{"if":["foo","binet",null]}`),
+					Metadata: map[string]interface{}{
+						"flagSetId": "flagSetId",
+					},
+					FlagSetId: "flagSetId",
+				},
+			},
 		},
 		"invalid targeting": {
 			inputState: `
diff --git a/core/pkg/evaluator/semver.go b/core/pkg/evaluator/semver.go
index 9d338a359..56327780d 100644
--- a/core/pkg/evaluator/semver.go
+++ b/core/pkg/evaluator/semver.go
@@ -85,12 +85,12 @@ func (je *SemVerComparison) SemVerEvaluation(values, _ interface{}) interface{}
 	actualVersion, targetVersion, operator, err := parseSemverEvaluationData(values)
 	if err != nil {
 		je.Logger.Error(fmt.Sprintf("parse sem_ver evaluation data: %v", err))
-		return false
+		return nil
 	}
 	res, err := operator.compare(actualVersion, targetVersion)
 	if err != nil {
 		je.Logger.Error(fmt.Sprintf("sem_ver evaluation: %v", err))
-		return false
+		return nil
 	}
 	return res
 }
@@ -105,7 +105,7 @@ func parseSemverEvaluationData(values interface{}) (string, string, SemVerOperat
 		return "", "", "", errors.New("sem_ver evaluation must contain a value, an operator, and a comparison target")
 	}
 
-	actualVersion, err := parseSemanticVersion(parsed[0])
+	actualVersion, err := normalizeVersion(parsed[0])
 	if err != nil {
 		return "", "", "", fmt.Errorf("sem_ver evaluation: could not parse target property value: %w", err)
 	}
@@ -115,7 +115,7 @@ func parseSemverEvaluationData(values interface{}) (string, string, SemVerOperat
 		return "", "", "", fmt.Errorf("sem_ver evaluation: could not parse operator: %w", err)
 	}
 
-	targetVersion, err := parseSemanticVersion(parsed[2])
+	targetVersion, err := normalizeVersion(parsed[2])
 	if err != nil {
 		return "", "", "", fmt.Errorf("sem_ver evaluation: could not parse target value: %w", err)
 	}
@@ -131,11 +131,13 @@ func ensureString(v interface{}) string {
 	return fmt.Sprintf("%v", v)
 }
 
-func parseSemanticVersion(v interface{}) (string, error) {
+func normalizeVersion(v interface{}) (string, error) {
 	version := ensureString(v)
 	// version strings are only valid in the semver package if they start with a 'v'
 	// if it's not present in the given value, we prepend it
+	// 'V' is normalized to 'v'
 	if !strings.HasPrefix(version, "v") {
+		version = strings.TrimPrefix(version, "V")
 		version = "v" + version
 	}
 
diff --git a/core/pkg/evaluator/semver_test.go b/core/pkg/evaluator/semver_test.go
index 0d25af9cc..47b61b371 100644
--- a/core/pkg/evaluator/semver_test.go
+++ b/core/pkg/evaluator/semver_test.go
@@ -2,12 +2,9 @@ package evaluator
 
 import (
 	"context"
-	"errors"
 	"testing"
 
-	"github.com/open-feature/flagd/core/pkg/logger"
 	"github.com/open-feature/flagd/core/pkg/model"
-	"github.com/open-feature/flagd/core/pkg/store"
 	"github.com/stretchr/testify/require"
 )
 
@@ -83,6 +80,16 @@ func TestSemVerOperator_Compare(t *testing.T) {
 			want:    true,
 			wantErr: false,
 		},
+		{
+			name: "uppercase V prefix equals lowercase or no prefix",
+			svo:  Equals,
+			args: args{
+				v1: "V1.0.0",
+				v2: "1.0.0",
+			},
+			want:    true,
+			wantErr: false,
+		},
 		{
 			name: "no prefixed v both",
 			svo:  Greater,
@@ -320,15 +327,7 @@ func TestJSONEvaluator_semVerEvaluation(t *testing.T) {
 	var sources = []string{source}
 	ctx := context.Background()
 
-	tests := map[string]struct {
-		flags           []model.Flag
-		flagKey         string
-		context         map[string]any
-		expectedValue   string
-		expectedVariant string
-		expectedReason  string
-		expectedError   error
-	}{
+	tests := map[string]stringFlagEvalTestCase{
 		"versions and operator provided - match": {
 			flags: []model.Flag{{
 				Key:            "headerColor",
@@ -789,34 +788,27 @@ func TestJSONEvaluator_semVerEvaluation(t *testing.T) {
 		},
 	}
 
-	const reqID = "default"
-	for name, tt := range tests {
-		t.Run(name, func(t *testing.T) {
-			log := logger.NewLogger(nil, false)
-			s, err := store.NewStore(log, sources)
-			if err != nil {
-				t.Fatalf("NewStore failed: %v", err)
-			}
-			je := NewJSON(log, s)
-			je.store.Update(source, tt.flags, model.Metadata{}, false)
-
-			value, variant, reason, _, err := resolve[string](ctx, reqID, tt.flagKey, tt.context, je.evaluateVariant)
-
-			if value != tt.expectedValue {
-				t.Errorf("expected value '%s', got '%s'", tt.expectedValue, value)
-			}
-
-			if variant != tt.expectedVariant {
-				t.Errorf("expected variant '%s', got '%s'", tt.expectedVariant, variant)
-			}
+	runStringFlagEvalTests(t, ctx, source, sources, tests)
+}
 
-			if reason != tt.expectedReason {
-				t.Errorf("expected reason '%s', got '%s'", tt.expectedReason, reason)
-			}
+func TestSemVerEvaluation_ErrorFallbackWhenUsedDirectly(t *testing.T) {
+	const source = "testSource"
+	ctx := context.Background()
 
-			if !errors.Is(err, tt.expectedError) {
-				t.Errorf("expected err '%v', got '%v'", tt.expectedError, err)
-			}
-		})
+	tests := map[string]errorFallbackTestCase{
+		"invalid context version falls back": {
+			targeting: `{"sem_ver": [{"var": "version"}, "=", "1.0.0"]}`,
+			context:   map[string]any{"version": "not-a-version"},
+		},
+		"invalid operator falls back": {
+			targeting: `{"sem_ver": [{"var": "version"}, "===", "1.0.0"]}`,
+			context:   map[string]any{"version": "1.0.0"},
+		},
+		"wrong arg count falls back": {
+			targeting: `{"sem_ver": [{"var": "version"}, "="]}`,
+			context:   map[string]any{"version": "1.0.0"},
+		},
 	}
+
+	runErrorFallbackTests(t, ctx, source, "semver-op-error-fallback", tests)
 }
diff --git a/core/pkg/evaluator/string_comparison.go b/core/pkg/evaluator/string_comparison.go
index d4a0d6b7c..9449b9430 100644
--- a/core/pkg/evaluator/string_comparison.go
+++ b/core/pkg/evaluator/string_comparison.go
@@ -72,7 +72,7 @@ func (sce *StringComparisonEvaluator) EndsWithEvaluation(values, _ interface{})
 	propertyValue, target, err := parseStringComparisonEvaluationData(values)
 	if err != nil {
 		sce.Logger.Error(fmt.Sprintf("parse ends_with evaluation data: %v", err))
-		return false
+		return nil
 	}
 	return strings.HasSuffix(propertyValue, target)
 }
diff --git a/core/pkg/evaluator/string_comparison_test.go b/core/pkg/evaluator/string_comparison_test.go
index 01905a446..9049caf15 100644
--- a/core/pkg/evaluator/string_comparison_test.go
+++ b/core/pkg/evaluator/string_comparison_test.go
@@ -2,13 +2,10 @@ package evaluator
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"testing"
 
-	"github.com/open-feature/flagd/core/pkg/logger"
 	"github.com/open-feature/flagd/core/pkg/model"
-	"github.com/open-feature/flagd/core/pkg/store"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -17,21 +14,13 @@ func TestJSONEvaluator_startsWithEvaluation(t *testing.T) {
 	var sources = []string{source}
 	ctx := context.Background()
 
-	tests := map[string]struct {
-		flags           []model.Flag
-		flagKey         string
-		context         map[string]any
-		expectedValue   string
-		expectedVariant string
-		expectedReason  string
-		expectedError   error
-	}{
+	tests := map[string]stringFlagEvalTestCase{
 		"two strings provided - match": {
 			flags: []model.Flag{{
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -55,7 +44,7 @@ func TestJSONEvaluator_startsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -79,7 +68,7 @@ func TestJSONEvaluator_startsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -103,7 +92,7 @@ func TestJSONEvaluator_startsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -127,7 +116,7 @@ func TestJSONEvaluator_startsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -148,36 +137,7 @@ func TestJSONEvaluator_startsWithEvaluation(t *testing.T) {
 		},
 	}
 
-	const reqID = "default"
-	for name, tt := range tests {
-		t.Run(name, func(t *testing.T) {
-			log := logger.NewLogger(nil, false)
-			s, err := store.NewStore(log, sources)
-			if err != nil {
-				t.Fatalf("NewStore failed: %v", err)
-			}
-			je := NewJSON(log, s)
-			je.store.Update(source, tt.flags, model.Metadata{}, false)
-
-			value, variant, reason, _, err := resolve[string](ctx, reqID, tt.flagKey, tt.context, je.evaluateVariant)
-
-			if value != tt.expectedValue {
-				t.Errorf("expected value '%s', got '%s'", tt.expectedValue, value)
-			}
-
-			if variant != tt.expectedVariant {
-				t.Errorf("expected variant '%s', got '%s'", tt.expectedVariant, variant)
-			}
-
-			if reason != tt.expectedReason {
-				t.Errorf("expected reason '%s', got '%s'", tt.expectedReason, reason)
-			}
-
-			if !errors.Is(err, tt.expectedError) {
-				t.Errorf("expected err '%v', got '%v'", tt.expectedError, err)
-			}
-		})
-	}
+	runStringFlagEvalTests(t, ctx, source, sources, tests)
 }
 
 func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
@@ -185,21 +145,13 @@ func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
 	var sources = []string{source}
 	ctx := context.Background()
 
-	tests := map[string]struct {
-		flags           []model.Flag
-		flagKey         string
-		context         map[string]any
-		expectedValue   string
-		expectedVariant string
-		expectedReason  string
-		expectedError   error
-	}{
+	tests := map[string]stringFlagEvalTestCase{
 		"two strings provided - match": {
 			flags: []model.Flag{{
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -223,7 +175,7 @@ func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -247,7 +199,7 @@ func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -271,7 +223,7 @@ func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -295,7 +247,7 @@ func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
 				Key:            "headerColor",
 				State:          "ENABLED",
 				DefaultVariant: "red",
-				Variants: colorVariants,
+				Variants:       colorVariants,
 				Targeting: []byte(`{
 											"if": [
 											  {
@@ -316,36 +268,7 @@ func TestJSONEvaluator_endsWithEvaluation(t *testing.T) {
 		},
 	}
 
-	const reqID = "default"
-	for name, tt := range tests {
-		t.Run(name, func(t *testing.T) {
-			log := logger.NewLogger(nil, false)
-			s, err := store.NewStore(log, sources)
-			if err != nil {
-				t.Fatalf("NewStore failed: %v", err)
-			}
-			je := NewJSON(log, s)
-			je.store.Update(source, tt.flags, model.Metadata{}, false)
-
-			value, variant, reason, _, err := resolve[string](ctx, reqID, tt.flagKey, tt.context, je.evaluateVariant)
-
-			if value != tt.expectedValue {
-				t.Errorf("expected value '%s', got '%s'", tt.expectedValue, value)
-			}
-
-			if variant != tt.expectedVariant {
-				t.Errorf("expected variant '%s', got '%s'", tt.expectedVariant, variant)
-			}
-
-			if reason != tt.expectedReason {
-				t.Errorf("expected reason '%s', got '%s'", tt.expectedReason, reason)
-			}
-
-			if err != tt.expectedError {
-				t.Errorf("expected err '%v', got '%v'", tt.expectedError, err)
-			}
-		})
-	}
+	runStringFlagEvalTests(t, ctx, source, sources, tests)
 }
 
 func Test_parseStringComparisonEvaluationData(t *testing.T) {
@@ -431,3 +354,21 @@ func Test_parseStringComparisonEvaluationData(t *testing.T) {
 		})
 	}
 }
+
+func TestStringComparisonEvaluation_ErrorFallbackWhenUsedDirectly(t *testing.T) {
+	const source = "testSource"
+	ctx := context.Background()
+
+	tests := map[string]errorFallbackTestCase{
+		"starts_with invalid input falls back": {
+			targeting: `{"starts_with": [{"var": "num"}, "abc"]}`,
+			context:   map[string]any{"num": 123.0},
+		},
+		"ends_with invalid input falls back": {
+			targeting: `{"ends_with": [{"var": "num"}, "xyz"]}`,
+			context:   map[string]any{"num": 123.0},
+		},
+	}
+
+	runErrorFallbackTests(t, ctx, source, "string-op-error-fallback", tests)
+}
diff --git a/core/pkg/evaluator/utils_test.go b/core/pkg/evaluator/utils_test.go
index 3a9cde66d..d466d364a 100644
--- a/core/pkg/evaluator/utils_test.go
+++ b/core/pkg/evaluator/utils_test.go
@@ -1,8 +1,84 @@
 package evaluator
 
+import (
+	"context"
+	"testing"
+
+	"github.com/open-feature/flagd/core/pkg/logger"
+	"github.com/open-feature/flagd/core/pkg/model"
+	"github.com/open-feature/flagd/core/pkg/store"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
 var colorVariants = map[string]any{
 	"red":    "#FF0000",
 	"blue":   "#0000FF",
 	"green":  "#00FF00",
 	"yellow": "#FFFF00",
 }
+
+type stringFlagEvalTestCase struct {
+	flags           []model.Flag
+	flagKey         string
+	context         map[string]any
+	expectedValue   string
+	expectedVariant string
+	expectedReason  string
+	expectedError   error
+}
+
+func runStringFlagEvalTests(t *testing.T, ctx context.Context, source string, sources []string, tests map[string]stringFlagEvalTestCase) {
+	t.Helper()
+	const reqID = "default"
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			log := logger.NewLogger(nil, false)
+			s, err := store.NewStore(log, sources)
+			require.NoError(t, err)
+			je := NewJSON(log, s)
+			je.store.Update(source, tt.flags, model.Metadata{}, false)
+
+			value, variant, reason, _, err := resolve[string](ctx, reqID, tt.flagKey, tt.context, je.evaluateVariant)
+
+			assert.Equal(t, tt.expectedValue, value)
+			assert.Equal(t, tt.expectedVariant, variant)
+			assert.Equal(t, tt.expectedReason, reason)
+			assert.ErrorIs(t, err, tt.expectedError)
+		})
+	}
+}
+
+type errorFallbackTestCase struct {
+	targeting string
+	context   map[string]any
+}
+
+func runErrorFallbackTests(t *testing.T, ctx context.Context, source, flagKey string, tests map[string]errorFallbackTestCase) {
+	t.Helper()
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			log := logger.NewLogger(nil, false)
+			s, err := store.NewStore(log, []string{source})
+			require.NoError(t, err)
+			je := NewJSON(log, s)
+			je.store.Update(source, []model.Flag{{
+				Key:            flagKey,
+				State:          "ENABLED",
+				DefaultVariant: "fallback",
+				Variants: map[string]any{
+					"true":     "true",
+					"false":    "false",
+					"fallback": "fallback",
+				},
+				Targeting: []byte(tt.targeting),
+			}}, model.Metadata{}, false)
+
+			value, variant, reason, _, err := resolve[string](ctx, "default", flagKey, tt.context, je.evaluateVariant)
+			assert.NoError(t, err)
+			assert.Equal(t, "fallback", value)
+			assert.Equal(t, "fallback", variant)
+			assert.Equal(t, model.DefaultReason, reason)
+		})
+	}
+}
diff --git a/test-harness b/test-harness
index 2684a3ecf..190307b3b 160000
--- a/test-harness
+++ b/test-harness
@@ -1 +1 @@
-Subproject commit 2684a3ecf061002221a8be7d09e9c8f915c7b193
+Subproject commit 190307b3b1982773976f05464942f69bb23528a4
diff --git a/test/integration/go.mod b/test/integration/go.mod
index a79c0a3f8..e44c344a9 100644
--- a/test/integration/go.mod
+++ b/test/integration/go.mod
@@ -5,7 +5,7 @@ go 1.25.5
 
 require (
 	github.com/go-git/go-git/v5 v5.18.0
-	github.com/open-feature/go-sdk-contrib/providers/flagd v0.4.0
+	github.com/open-feature/go-sdk-contrib/providers/flagd v0.5.0
 	github.com/open-feature/go-sdk-contrib/tests/flagd/v2 v2.0.2
 	github.com/testcontainers/testcontainers-go v0.41.0
 )
@@ -115,7 +115,7 @@ require (
 	github.com/morikuni/aec v1.1.0 // indirect
 	github.com/onsi/gomega v1.35.1 // indirect
 	github.com/open-feature/flagd-schemas v0.2.13 // indirect
-	github.com/open-feature/flagd/core v0.14.0 // indirect
+	github.com/open-feature/flagd/core v0.15.0 // indirect
 	github.com/open-feature/go-sdk v1.17.0 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.1.1 // indirect
@@ -158,10 +158,10 @@ require (
 	go.opentelemetry.io/contrib/instrumentation/net/http/httptrace/otelhttptrace v0.63.0 // indirect
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0 // indirect
 	go.opentelemetry.io/otel v1.43.0 // indirect
-	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.38.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.43.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.43.0 // indirect
-	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.38.0 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.42.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.43.0 // indirect
 	go.opentelemetry.io/otel/metric v1.43.0 // indirect
 	go.opentelemetry.io/otel/sdk v1.43.0 // indirect
@@ -170,7 +170,7 @@ require (
 	go.opentelemetry.io/proto/otlp v1.10.0 // indirect
 	go.uber.org/mock v0.6.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
-	go.uber.org/zap v1.27.0 // indirect
+	go.uber.org/zap v1.27.1 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
 	go.yaml.in/yaml/v4 v4.0.0-rc.4 // indirect
 	golang.org/x/crypto v0.49.0 // indirect
diff --git a/test/integration/go.sum b/test/integration/go.sum
index 118dada17..8f7d4d37c 100644
--- a/test/integration/go.sum
+++ b/test/integration/go.sum
@@ -253,8 +253,9 @@ github.com/hashicorp/go-memdb v1.3.5/go.mod h1:8IVKKBkVe+fxFgdFOYxzQQNjz+sWCyHCd
 github.com/hashicorp/go-multierror v1.1.1 h1:H5DkEtf6CXdFp0N0Em5UCwQpXMWke8IA0+lD48awMYo=
 github.com/hashicorp/go-multierror v1.1.1/go.mod h1:iw975J/qwKPdAO1clOe2L8331t/9/fmwbPZ6JB6eMoM=
 github.com/hashicorp/go-uuid v1.0.0/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
-github.com/hashicorp/go-uuid v1.0.2 h1:cfejS+Tpcp13yd5nYHWDI6qVCny6wyX2Mt5SGur2IGE=
 github.com/hashicorp/go-uuid v1.0.2/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
+github.com/hashicorp/go-uuid v1.0.3 h1:2gKiV6YVmrJ1i2CKKa9obLvRieoRGviZFL26PcT/Co8=
+github.com/hashicorp/go-uuid v1.0.3/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
 github.com/hashicorp/go-version v1.8.0 h1:KAkNb1HAiZd1ukkxDFGmokVZe1Xy9HG6NUp+bPle2i4=
 github.com/hashicorp/go-version v1.8.0/go.mod h1:fltr4n8CU8Ke44wwGCBoEymUuxUHl09ZGVZPK5anwXA=
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
@@ -343,12 +344,12 @@ github.com/onsi/gomega v1.35.1 h1:Cwbd75ZBPxFSuZ6T+rN/WCb/gOc6YgFBXLlZLhC7Ds4=
 github.com/onsi/gomega v1.35.1/go.mod h1:PvZbdDc8J6XJEpDK4HCuRBm8a6Fzp9/DmhC9C7yFlog=
 github.com/open-feature/flagd-schemas v0.2.13 h1:LzoyQfirfpR8cxI4PKnoFRtpwPjpC/cOO8N0n8dpbRc=
 github.com/open-feature/flagd-schemas v0.2.13/go.mod h1:C0jnJ4C3j2LzGuqKgLDdTsdfKEWQp6sOHZyxu3QohFU=
-github.com/open-feature/flagd/core v0.14.0 h1:eGjPKONDjGa0+Pkxi6XiTdusFUCN3EuF7b1aebcDPvM=
-github.com/open-feature/flagd/core v0.14.0/go.mod h1:G1KZQoSD0gi6JMVwcZxHhzOhs/WnhoyPjZneqej1neI=
+github.com/open-feature/flagd/core v0.15.0 h1:y8ZEj1Ia8xHQiSugoRpWW4t1kvc+l5bLqWwPzO5avr0=
+github.com/open-feature/flagd/core v0.15.0/go.mod h1:J+Hz06ZMPymRiXR9WGA/nMYjtVKzuHC9LSrz81GxJIE=
 github.com/open-feature/go-sdk v1.17.0 h1:/OUBBw5d9D61JaNZZxb2Nnr5/EJrEpjtKCTY3rspJQk=
 github.com/open-feature/go-sdk v1.17.0/go.mod h1:lPxPSu1UnZ4E3dCxZi5gV3et2ACi8O8P+zsTGVsDZUw=
-github.com/open-feature/go-sdk-contrib/providers/flagd v0.4.0 h1:FHcz/EQ+WtPrbrtB9XBbrOKnpXk2sHyIwLo7pFt2wm4=
-github.com/open-feature/go-sdk-contrib/providers/flagd v0.4.0/go.mod h1:HcsGB/b695L9PZX9fZwpWU72tFQaj0wADbthStDaajE=
+github.com/open-feature/go-sdk-contrib/providers/flagd v0.5.0 h1:+zYgmk5JOhfaco0gnQ2gqAlGC6MTlIS0RN0ishPun6c=
+github.com/open-feature/go-sdk-contrib/providers/flagd v0.5.0/go.mod h1:bzGZZSSFPOkvptyFUOhZPUtjK0thkgNDOvQ4UcgUi/g=
 github.com/open-feature/go-sdk-contrib/tests/flagd/v2 v2.0.2 h1:deCtDKh3QKh6WXKDe6HzF6Gm01ZltVSF0JV5GhZbuRI=
 github.com/open-feature/go-sdk-contrib/tests/flagd/v2 v2.0.2/go.mod h1:oRuJpK7H5Alg8D3xGU2f/xJK/UqUqODIwhLMol6yo1Q=
 github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
@@ -380,10 +381,10 @@ github.com/prometheus/client_golang v1.23.2 h1:Je96obch5RDVy3FDMndoUsjAhG5Edi49h
 github.com/prometheus/client_golang v1.23.2/go.mod h1:Tb1a6LWHB3/SPIzCoaDXI4I8UHKeFTEQ1YCr+0Gyqmg=
 github.com/prometheus/client_model v0.6.2 h1:oBsgwpGs7iVziMvrGhE53c/GrLUsZdHnqNwqPLxwZyk=
 github.com/prometheus/client_model v0.6.2/go.mod h1:y3m2F6Gdpfy6Ut/GBsUqTWZqCUvMVzSfMLjcu6wAwpE=
-github.com/prometheus/common v0.66.1 h1:h5E0h5/Y8niHc5DlaLlWLArTQI7tMrsfQjHV+d9ZoGs=
-github.com/prometheus/common v0.66.1/go.mod h1:gcaUsgf3KfRSwHY4dIMXLPV0K/Wg1oZ8+SbZk/HH/dA=
-github.com/prometheus/procfs v0.17.0 h1:FuLQ+05u4ZI+SS/w9+BWEM2TXiHKsUQ9TADiRH7DuK0=
-github.com/prometheus/procfs v0.17.0/go.mod h1:oPQLaDAMRbA+u8H5Pbfq+dl3VDAvHxMUOVhe0wYB2zw=
+github.com/prometheus/common v0.67.5 h1:pIgK94WWlQt1WLwAC5j2ynLaBRDiinoAb86HZHTUGI4=
+github.com/prometheus/common v0.67.5/go.mod h1:SjE/0MzDEEAyrdr5Gqc6G+sXI67maCxzaT3A2+HqjUw=
+github.com/prometheus/procfs v0.20.1 h1:XwbrGOIplXW/AU3YhIhLODXMJYyC1isLFfYCsTEycfc=
+github.com/prometheus/procfs v0.20.1/go.mod h1:o9EMBZGRyvDrSPH1RqdxhojkuXstoe4UlK79eF5TGGo=
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 github.com/rivo/uniseg v0.4.7 h1:WUdvkW8uEhrYfLC4ZzdpI2ztxP1I582+49Oc5Mq64VQ=
 github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
@@ -496,14 +497,14 @@ go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0 h1:RbKq8BG
 go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.63.0/go.mod h1:h06DGIukJOevXaj/xrNjhi/2098RZzcLTbc0jDAUbsg=
 go.opentelemetry.io/otel v1.43.0 h1:mYIM03dnh5zfN7HautFE4ieIig9amkNANT+xcVxAj9I=
 go.opentelemetry.io/otel v1.43.0/go.mod h1:JuG+u74mvjvcm8vj8pI5XiHy1zDeoCS2LB1spIq7Ay0=
-go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.38.0 h1:vl9obrcoWVKp/lwl8tRE33853I8Xru9HFbw/skNeLs8=
-go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.38.0/go.mod h1:GAXRxmLJcVM3u22IjTg74zWBrRCKq8BnOqUVLodpcpw=
+go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0 h1:MdKucPl/HbzckWWEisiNqMPhRrAOQX8r4jTuGr636gk=
+go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.42.0/go.mod h1:RolT8tWtfHcjajEH5wFIZ4Dgh5jpPdFXYV9pTAk/qjc=
 go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.43.0 h1:w1K+pCJoPpQifuVpsKamUdn9U0zM3xUziVOqsGksUrY=
 go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.43.0/go.mod h1:HBy4BjzgVE8139ieRI75oXm3EcDN+6GhD88JT1Kjvxg=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.43.0 h1:88Y4s2C8oTui1LGM6bTWkw0ICGcOLCAI5l6zsD1j20k=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.43.0/go.mod h1:Vl1/iaggsuRlrHf/hfPJPvVag77kKyvrLeD10kpMl+A=
-go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.38.0 h1:lwI4Dc5leUqENgGuQImwLo4WnuXFPetmPpkLi2IrX54=
-go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.38.0/go.mod h1:Kz/oCE7z5wuyhPxsXDuaPteSWqjSBD5YaSdbxZYGbGk=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.42.0 h1:zWWrB1U6nqhS/k6zYB74CjRpuiitRtLLi68VcgmOEto=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.42.0/go.mod h1:2qXPNBX1OVRC0IwOnfo1ljoid+RD0QK3443EaqVlsOU=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.43.0 h1:3iZJKlCZufyRzPzlQhUIWVmfltrXuGyfjREgGP3UUjc=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.43.0/go.mod h1:/G+nUPfhq2e+qiXMGxMwumDrP5jtzU+mWN7/sjT2rak=
 go.opentelemetry.io/otel/metric v1.43.0 h1:d7638QeInOnuwOONPp4JAOGfbCEpYb+K6DVWvdxGzgM=
@@ -522,8 +523,8 @@ go.uber.org/mock v0.6.0 h1:hyF9dfmbgIX5EfOdasqLsWD6xqpNZlXblLB/Dbnwv3Y=
 go.uber.org/mock v0.6.0/go.mod h1:KiVJ4BqZJaMj4svdfmHM0AUx4NJYO8ZNpPnZn1Z+BBU=
 go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
 go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
-go.uber.org/zap v1.27.0 h1:aJMhYGrd5QSmlpLMr2MftRKl7t8J8PTZPA732ud/XR8=
-go.uber.org/zap v1.27.0/go.mod h1:GB2qFLM7cTU87MWRP2mPIjqfIDnGu+VIO4V/SdhGo2E=
+go.uber.org/zap v1.27.1 h1:08RqriUEv8+ArZRYSTXy1LeBScaMpVSTBhCeaZYfMYc=
+go.uber.org/zap v1.27.1/go.mod h1:GB2qFLM7cTU87MWRP2mPIjqfIDnGu+VIO4V/SdhGo2E=
 go.yaml.in/yaml/v2 v2.4.3 h1:6gvOSjQoTB3vt1l+CU+tSyi/HOjfOjRLJ4YwYZGwRO0=
 go.yaml.in/yaml/v2 v2.4.3/go.mod h1:zSxWcmIDjOzPXpjlTTbAsKokqkDNAVtZO0WOMiT90s8=
 go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
diff --git a/test/integration/integration_test.go b/test/integration/integration_test.go
index 48742626b..d286293e7 100644
--- a/test/integration/integration_test.go
+++ b/test/integration/integration_test.go
@@ -199,8 +199,13 @@ func TestInProcess(t *testing.T) {
 		"./",
 	}
 
-	// Run tests with InProcess-specific tags
-	tags := "@in-process && ~@unixsocket&& ~@metadata && ~@contextEnrichment && ~@customCert && ~@forbidden && ~@sync-port && ~@sync-payload && ~@fractional-v2 && ~@fractional-nested && ~@deprecated"
+	// Run tests with InProcess-specific tags.
+	// These tests use the published go-sdk-contrib in-process provider (see sibling go.mod),
+	// not the local flagd evaluator code. The goal is to verify the sync.proto interface,
+	// not to fully test the go in-process provider (that happens in go-sdk-contrib).
+	// Many tags are excluded because they require a more complex testbed than what's built here.
+	// TODO: remove ~@operator-errors and ~@semver-v-prefix once go-sdk-contrib picks up the fixes
+	tags := "@in-process && ~@unixsocket && ~@metadata && ~@contextEnrichment && ~@customCert && ~@forbidden && ~@sync-port && ~@sync-payload && ~@fractional-v1 && ~@fractional-single-entry && ~@deprecated && ~@operator-errors && ~@semver-v-prefix"
 
 	if err := runner.RunGherkinTestsWithSubtests(t, featurePaths, tags); err != nil {
 		t.Fatalf("Gherkin tests failed: %v", err)