fix(riva): avoid stale interim carryover in segment assembly

apps/sotto/internal/riva/client.go

@@ -41,12 +41,13 @@ type Stream struct {
 
 	recvDone chan struct{}
 
-	mu            sync.Mutex
-	segments      []string // committed transcript segments (final and pause-committed interim)
-	lastInterim   string
-	recvErr       error
-	closedSend    bool
-	debugSinkJSON io.Writer
+	mu                   sync.Mutex
+	segments             []string // committed transcript segments (final and high-confidence boundary-committed interim)
+	lastInterim          string
+	lastInterimStability float32
+	recvErr              error
+	closedSend           bool
+	debugSinkJSON        io.Writer
 }
 
 // DialStream establishes a stream, sends config, and starts the receive loop.

apps/sotto/internal/riva/client_test.go

@@ -50,7 +50,7 @@ func TestRecordResponseTracksInterimThenFinal(t *testing.T) {
 	require.Equal(t, []string{"hello world"}, s.segments)
 }
 
-func TestRecordResponseCommitsInterimAcrossPauseLikeReset(t *testing.T) {
+func TestRecordResponseReplacesDivergentInterimWithoutPrecommit(t *testing.T) {
 	s := &Stream{}
 
 	s.recordResponse(&asrpb.StreamingRecognizeResponse{
@@ -67,10 +67,89 @@ func TestRecordResponseCommitsInterimAcrossPauseLikeReset(t *testing.T) {
 		}},
 	})
 
+	require.Empty(t, s.segments)
+	segments := collectSegments(s.segments, s.lastInterim)
+	require.Equal(t, []string{"second phrase"}, segments)
+}
+
+func TestRecordResponseCommitsStableDivergentInterimForPartialRecovery(t *testing.T) {
+	s := &Stream{}
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      false,
+			Stability:    0.95,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "first phrase"}},
+		}},
+	})
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      false,
+			Stability:    0.20,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "second phrase"}},
+		}},
+	})
+
+	require.Equal(t, []string{"first phrase"}, s.segments)
 	segments := collectSegments(s.segments, s.lastInterim)
 	require.Equal(t, []string{"first phrase", "second phrase"}, segments)
 }
 
+func TestRecordResponseDoesNotPrependStaleInterimBeforeFinal(t *testing.T) {
+	s := &Stream{}
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      false,
+			Stability:    0.05,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "stale words"}},
+		}},
+	})
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      false,
+			Stability:    0.30,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "hello world"}},
+		}},
+	})
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      true,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "hello world"}},
+		}},
+	})
+
+	segments := collectSegments(s.segments, s.lastInterim)
+	require.Equal(t, []string{"hello world"}, segments)
+}
+
+func TestRecordResponseTreatsSuffixCorrectionAsContinuation(t *testing.T) {
+	s := &Stream{}
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      false,
+			Stability:    0.95,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "replace reply replied on the review thread with details"}},
+		}},
+	})
+
+	s.recordResponse(&asrpb.StreamingRecognizeResponse{
+		Results: []*asrpb.StreamingRecognitionResult{{
+			IsFinal:      false,
+			Stability:    0.95,
+			Alternatives: []*asrpb.SpeechRecognitionAlternative{{Transcript: "replied on the review thread with details"}},
+		}},
+	})
+
+	require.Empty(t, s.segments)
+	segments := collectSegments(s.segments, s.lastInterim)
+	require.Equal(t, []string{"replied on the review thread with details"}, segments)
+}
+
 func TestAppendSegmentDedupAndPrefixMerge(t *testing.T) {
 	segments := appendSegment(nil, "hello")
 	require.Equal(t, []string{"hello"}, segments)
@@ -94,7 +173,13 @@ func TestCleanSegmentAndInterimContinuation(t *testing.T) {
 
 	require.True(t, isInterimContinuation("hello", "hello world"))
 	require.True(t, isInterimContinuation("hello world", "hello"))
+	require.True(t, isInterimContinuation("replace reply replied on thread", "replied on thread"))
 	require.False(t, isInterimContinuation("first phrase", "second phrase"))
+
+	require.False(t, shouldCommitPriorInterimOnDivergence("first phrase", 0.2, "second phrase"))
+	require.True(t, shouldCommitPriorInterimOnDivergence("first phrase", 0.9, "second phrase"))
+	require.True(t, shouldCommitPriorInterimOnDivergence("Done.", 0.1, "new sentence"))
+	require.False(t, shouldCommitPriorInterimOnDivergence("replace reply replied on thread", 0.95, "replied on thread"))
 }
 
 func TestDialStreamEndToEndWithDebugSinkAndSpeechContexts(t *testing.T) {

apps/sotto/internal/riva/stream_receive.go

@@ -53,12 +53,14 @@ func (s *Stream) recordResponse(resp *asrpb.StreamingRecognizeResponse) {
 		if result.GetIsFinal() {
 			s.segments = appendSegment(s.segments, transcript)
 			s.lastInterim = ""
+			s.lastInterimStability = 0
 			continue
 		}
 
-		if s.lastInterim != "" && !isInterimContinuation(s.lastInterim, transcript) {
+		if shouldCommitPriorInterimOnDivergence(s.lastInterim, s.lastInterimStability, transcript) {
 			s.segments = appendSegment(s.segments, s.lastInterim)
 		}
 		s.lastInterim = transcript
+		s.lastInterimStability = result.GetStability()
 	}
 }

apps/sotto/internal/riva/transcript_segments.go

@@ -2,6 +2,8 @@ package riva
 
 import "strings"
 
+const stableInterimBoundaryThreshold = 0.85
+
 // collectSegments appends a valid trailing interim segment when needed.
 func collectSegments(committedSegments []string, lastInterim string) []string {
 	segments := append([]string(nil), committedSegments...)
@@ -48,18 +50,62 @@ func isInterimContinuation(previous string, current string) bool {
 	if strings.HasPrefix(current, previous) || strings.HasPrefix(previous, current) {
 		return true
 	}
+	if strings.HasSuffix(current, previous) || strings.HasSuffix(previous, current) {
+		return true
+	}
 
 	prevWords := strings.Fields(previous)
 	currWords := strings.Fields(current)
-	common := commonPrefixWords(prevWords, currWords)
 	shorter := len(prevWords)
 	if len(currWords) < shorter {
 		shorter = len(currWords)
 	}
 	if shorter == 0 {
 		return true
 	}
-	return common*2 >= shorter
+
+	commonPrefix := commonPrefixWords(prevWords, currWords)
+	if commonPrefix*2 >= shorter {
+		return true
+	}
+
+	commonSuffix := commonSuffixWords(prevWords, currWords)
+	if shorter >= 3 && commonSuffix*2 >= shorter {
+		return true
+	}
+
+	return false
+}
+
+// shouldCommitPriorInterimOnDivergence decides whether to preserve prior interim
+// text when a new interim hypothesis diverges.
+func shouldCommitPriorInterimOnDivergence(previous string, previousStability float32, current string) bool {
+	previous = cleanSegment(previous)
+	current = cleanSegment(current)
+	if previous == "" || current == "" {
+		return false
+	}
+	if isInterimContinuation(previous, current) {
+		return false
+	}
+	if previousStability >= stableInterimBoundaryThreshold {
+		return true
+	}
+	return endsWithSentencePunctuation(previous)
+}
+
+// endsWithSentencePunctuation reports whether transcript looks sentence-complete.
+func endsWithSentencePunctuation(transcript string) bool {
+	transcript = strings.TrimSpace(transcript)
+	if transcript == "" {
+		return false
+	}
+	switch transcript[len(transcript)-1] {
+	case '.', '!', '?':
+		return true
+	default:
+		return false
+	}
 }
 
 // commonPrefixWords counts shared leading words across two slices.
@@ -78,6 +124,22 @@ func commonPrefixWords(left []string, right []string) int {
 	return count
 }
 
+// commonSuffixWords counts shared trailing words across two slices.
+func commonSuffixWords(left []string, right []string) int {
+	li := len(left) - 1
+	ri := len(right) - 1
+	count := 0
+	for li >= 0 && ri >= 0 {
+		if left[li] != right[ri] {
+			break
+		}
+		count++
+		li--
+		ri--
+	}
+	return count
+}
+
 // cleanSegment normalizes transcript whitespace.
 func cleanSegment(raw string) string {
 	raw = strings.TrimSpace(raw)