diff --git a/activity/synthesis.go b/activity/synthesis.go
index 2ea9551..63a8777 100644
--- a/activity/synthesis.go
+++ b/activity/synthesis.go
@@ -148,6 +148,23 @@ func (s *SynthesisActivities) ExtractFactsActivity(ctx context.Context, chunkID
 			subject := strings.TrimSpace(match[1])
 			object := strings.TrimSpace(match[2])
 
+			// Validation: skip empty or invalid extracts
+			if len(subject) == 0 || len(object) == 0 {
+				continue // Skip empty subject/object
+			}
+
+			// Truncate overly long objects (avoid capturing entire sentence)
+			if len(object) > 500 {
+				logger.Info("truncating long object", "original_len", len(object), "subject", subject, "predicate", vp.predicate)
+				object = object[:500]
+			}
+
+			// Truncate overly long subjects
+			if len(subject) > 200 {
+				logger.Info("truncating long subject", "original_len", len(subject), "predicate", vp.predicate)
+				subject = subject[:200]
+			}
+
 			// Boost confidence if subject/object are known entities
 			confidence := 0.60
 			if entityNames[strings.ToLower(subject)] {
@@ -226,6 +243,7 @@ func (s *SynthesisActivities) DetectContradictionsActivity(ctx context.Context,
 
 // PersistSynthesisActivity saves all synthesis results to the memory service.
 // Stage 5: Persists entities, facts, and queues contradictions for review.
+// Returns error if any persistence fails (fail-safe semantics).
 func (s *SynthesisActivities) PersistSynthesisActivity(ctx context.Context, input PersistInput) error {
 	logger := slog.Default()
 	logger.Info("persisting synthesis results",
@@ -235,6 +253,8 @@ func (s *SynthesisActivities) PersistSynthesisActivity(ctx context.Context, inpu
 		"contradictions", len(input.Contradictions),
 	)
 
+	var errs []error
+
 	// Persist entities as knowledge records
 	for _, entity := range input.Entities {
 		_, err := s.memClient.Ingest(ctx, &memory.IngestRequest{
@@ -249,7 +269,8 @@ func (s *SynthesisActivities) PersistSynthesisActivity(ctx context.Context, inpu
 			},
 		})
 		if err != nil {
-			logger.Warn("failed to persist entity", "entity", entity.Name, "error", err)
+			logger.Error("failed to persist entity", "entity", entity.Name, "error", err)
+			errs = append(errs, fmt.Errorf("persist entity %s: %w", entity.Name, err))
 		}
 	}
 
@@ -268,11 +289,18 @@ func (s *SynthesisActivities) PersistSynthesisActivity(ctx context.Context, inpu
 			},
 		})
 		if err != nil {
-			logger.Warn("failed to persist fact", "subject", fact.Subject, "error", err)
+			logger.Error("failed to persist fact", "subject", fact.Subject, "predicate", fact.Predicate, "error", err)
+			errs = append(errs, fmt.Errorf("persist fact %s %s: %w", fact.Subject, fact.Predicate, err))
 		}
 	}
 
-	logger.Info("synthesis persisted", "chunk_id", input.ChunkID)
+	// Return all accumulated errors (fail-safe semantics)
+	if len(errs) > 0 {
+		logger.Error("persistence failed with errors", "error_count", len(errs), "chunk_id", input.ChunkID)
+		return fmt.Errorf("persist synthesis: %d errors - %v", len(errs), errs)
+	}
+
+	logger.Info("synthesis persisted successfully", "chunk_id", input.ChunkID)
 	return nil
 }
 
diff --git a/activity/synthesis_test.go b/activity/synthesis_test.go
index 938479c..b8a0fea 100644
--- a/activity/synthesis_test.go
+++ b/activity/synthesis_test.go
@@ -2,6 +2,7 @@ package activity
 
 import (
 	"context"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -120,6 +121,58 @@ func TestClassifyEntity(t *testing.T) {
 	assert.Equal(t, "concept", classifyEntity("SomeRandomThing"))
 }
 
+// --- Tests for ExtractFactsActivity Validation ---
+
+func TestExtractFacts_WithValidation(t *testing.T) {
+	sa := NewSynthesisActivities(nil)
+	// Test with very long object that should be truncated
+	longText := "Kubernetes uses " + strings.Repeat("very long object name that should be truncated ", 20)
+	entities := []ExtractedEntity{}
+
+	facts, err := sa.ExtractFactsActivity(testCtx, "chunk-1", longText, entities)
+	assert.NoError(t, err)
+
+	// Verify no fact has object > 500 chars
+	for _, f := range facts {
+		assert.LessOrEqual(t, len(f.Object), 500, "object should be truncated to 500 chars")
+	}
+}
+
+func TestExtractFacts_SkipsEmpty(t *testing.T) {
+	sa := NewSynthesisActivities(nil)
+	// Text with empty patterns that would extract nothing
+	text := "Something uses  and other things"
+	entities := []ExtractedEntity{}
+
+	facts, err := sa.ExtractFactsActivity(testCtx, "chunk-1", text, entities)
+	assert.NoError(t, err)
+
+	// Verify no empty facts
+	for _, f := range facts {
+		assert.NotEmpty(t, f.Subject, "subject should not be empty")
+		assert.NotEmpty(t, f.Object, "object should not be empty")
+	}
+}
+
+func TestPersistSynthesis_EmptyInput(t *testing.T) {
+	// Test that empty input is handled (no entities or facts to persist)
+	// Note: This test requires a mock memory service; for now we just test structure
+	input := PersistInput{
+		ChunkID:        "chunk-123",
+		Project:        "test",
+		Source:         "test://1",
+		Kind:           "L1",
+		Entities:       []ExtractedEntity{}, // Empty
+		Facts:          []ExtractedFact{},  // Empty
+		Contradictions: []ContradictionResult{},
+	}
+
+	// Verify input structure is valid
+	assert.Equal(t, "chunk-123", input.ChunkID)
+	assert.Equal(t, 0, len(input.Entities))
+	assert.Equal(t, 0, len(input.Facts))
+}
+
 // helper
 func entityNames(entities []ExtractedEntity) []string {
 	names := make([]string, len(entities))