diff --git a/modules/interaction/domain/semantics.go b/modules/interaction/domain/semantics.go
index 84ec283..0531848 100644
--- a/modules/interaction/domain/semantics.go
+++ b/modules/interaction/domain/semantics.go
@@ -29,6 +29,7 @@ func InterpretUtterance(utterance interaction.HumanUtterance, projects []situati
 	millis := now.UnixMilli()
 	deterministicCandidate := BuildDeterministicCandidate(utterance.Content, utterance.CorrectsUtteranceID, millis)
 	deterministicCandidate.UtteranceID = utterance.ID
+	deterministicCandidate.SelectionState = interaction.CandidateSelected
 	selectedCandidate := deterministicCandidate
 	result := SemanticResult{
 		Interpretation: interaction.UtteranceInterpretation{
@@ -103,14 +104,18 @@ func ApplyCognitiveCandidate(result SemanticResult, message string, candidate in
 
 	matched := false
 	for index := range result.Candidates {
-		if result.Candidates[index].SelectionState == interaction.CandidateSelected {
-			result.Candidates[index].SelectionState = interaction.CandidateObserved
-		}
 		if result.Candidates[index].ID == candidate.ID {
 			result.Candidates[index] = candidate
 			matched = true
 		}
 	}
+	if selected {
+		for index := range result.Candidates {
+			if result.Candidates[index].ID != candidate.ID && result.Candidates[index].SelectionState == interaction.CandidateSelected {
+				result.Candidates[index].SelectionState = interaction.CandidateObserved
+			}
+		}
+	}
 	if !matched {
 		result.Candidates = append(result.Candidates, candidate)
 	}
diff --git a/modules/interaction/domain/semantics_test.go b/modules/interaction/domain/semantics_test.go
index ade21f6..810ed62 100644
--- a/modules/interaction/domain/semantics_test.go
+++ b/modules/interaction/domain/semantics_test.go
@@ -119,10 +119,10 @@ func TestInterpretUtteranceAmbiguousDestructiveRequiresClarification(t *testing.
 
 func TestInterpretUtteranceNaturalRussianHelpflowUsesContextAwareCognitionInput(t *testing.T) {
 	cases := []struct {
-		message         string
-		wantSpeech      interaction.SpeechAct
-		wantCognition   bool
-		allowNoMatch    bool
+		message       string
+		wantSpeech    interaction.SpeechAct
+		wantCognition bool
+		allowNoMatch  bool
 	}{
 		{message: "расскажи как это работает", wantSpeech: interaction.SpeechActQuestion, wantCognition: true},
 		{message: "Расскажи, как это работает?", wantSpeech: interaction.SpeechActQuestion, wantCognition: true},
@@ -325,6 +325,49 @@ func TestInterpretUtteranceModalExplanationRequestStillRequestsCognition(t *test
 	}
 }
 
+func TestInterpretUtteranceSelectsDeterministicCandidateByDefault(t *testing.T) {
+	result := interpretForTest(t, "основная база называется UPO", nil, "")
+	if len(result.Candidates) != 1 {
+		t.Fatalf("expected one deterministic candidate, got %d", len(result.Candidates))
+	}
+	if result.Candidates[0].SelectionState != interaction.CandidateSelected {
+		t.Fatalf("deterministic candidate must be selected by default, got %s", result.Candidates[0].SelectionState)
+	}
+}
+
+func TestRejectedCognitiveCandidatePreservesSelectedDeterministicCandidate(t *testing.T) {
+	result := interpretForTest(t, "основная база называется UPO", nil, "")
+	candidateID, err := ids.New()
+	if err != nil {
+		t.Fatal(err)
+	}
+	rejected := interaction.SemanticCandidate{
+		ID:                 interaction.SemanticCandidateID(candidateID),
+		UtteranceID:        result.Interpretation.UtteranceID,
+		Source:             interaction.CandidateSourceCognitive,
+		PrimarySpeechAct:   interaction.SpeechActQuestion,
+		SecondarySpeechAct: interaction.SpeechActUnknown,
+		ConfidenceMillis:   700,
+		Applicability:      interaction.SemanticApplicable,
+		Clarification:      interaction.ClarificationNotRequired,
+		NeedsCognition:     false,
+		SelectionReason:    "must not replace a safe assertion with an unrelated candidate",
+	}
+	result = ApplyCognitiveCandidate(result, "основная база называется UPO", rejected, nil)
+	selected := 0
+	for _, candidate := range result.Candidates {
+		if candidate.SelectionState == interaction.CandidateSelected {
+			selected++
+			if candidate.Source != interaction.CandidateSourceDeterministic {
+				t.Fatalf("rejected cognitive candidate replaced deterministic selection: %#v", candidate)
+			}
+		}
+	}
+	if selected != 1 {
+		t.Fatalf("expected exactly one selected candidate after rejection, got %d", selected)
+	}
+}
+
 func interpretForTest(t *testing.T, message string, previous *situation.ActiveProjectFocus, corrects interaction.HumanUtteranceID) SemanticResult {
 	t.Helper()
 	conversation := interaction.Conversation{ID: "conversation-1", ActorID: "actor-1", PrincipalID: "principal-1", Channel: interaction.ChannelWebChat, State: interaction.ConversationOpen}