Make module-stage LLM handling resilient and report warnings

internal/framework/proposals/apply.go

@@ -147,6 +147,8 @@ func skipReasonMessage(reason ProposalSkipReason) string {
 		return "original_text matched multiple spans under require_unique policy"
 	case SkipReasonNoEffect:
 		return "original_text and corrected_text are identical"
+	case SkipReasonEmptyResultingText:
+		return "proposal would leave the segment empty"
 	case SkipReasonInvalidProposal:
 		return "proposal failed structural or policy validation"
 	default:

internal/framework/proposals/preview.go

@@ -15,6 +15,7 @@ const (
 	SkipReasonMissingOriginalText ProposalSkipReason = "missing_original_text"
 	SkipReasonAmbiguousOriginal   ProposalSkipReason = "ambiguous_original_text"
 	SkipReasonNoEffect            ProposalSkipReason = "no_effect"
+	SkipReasonEmptyResultingText  ProposalSkipReason = "empty_resulting_segment"
 	SkipReasonInvalidProposal     ProposalSkipReason = "invalid_proposal"
 )
 
@@ -62,6 +63,9 @@ func PreviewProposalForSegment(segment *schema.Segment, proposal CorrectionPropo
 		}
 
 		corrected := strings.Replace(segment.Text, proposal.OriginalText, proposal.CorrectedText, 1)
+		if strings.TrimSpace(corrected) == "" {
+			return SegmentPreviewResult{SkipReason: SkipReasonEmptyResultingText}
+		}
 		return SegmentPreviewResult{
 			Applicable:           true,
 			CorrectedSegmentText: corrected,
@@ -70,6 +74,9 @@ func PreviewProposalForSegment(segment *schema.Segment, proposal CorrectionPropo
 
 	case ReplacementPolicyReplaceAll:
 		corrected := strings.ReplaceAll(segment.Text, proposal.OriginalText, proposal.CorrectedText)
+		if strings.TrimSpace(corrected) == "" {
+			return SegmentPreviewResult{SkipReason: SkipReasonEmptyResultingText}
+		}
 		return SegmentPreviewResult{
 			Applicable:           true,
 			CorrectedSegmentText: corrected,

internal/framework/proposals/preview_test.go

@@ -121,6 +121,42 @@ func TestPreviewProposalForSegmentNoEffectReplacement(t *testing.T) {
 	}
 }
 
+func TestPreviewProposalForSegmentAllowsEmptyCorrectedTextWhenSegmentRemainsNonEmpty(t *testing.T) {
+	segment := &schema.Segment{ID: 8, Text: "uh hello"}
+	proposal := CorrectionProposal{
+		TargetSegmentID: 8,
+		OriginalText:    "uh ",
+		CorrectedText:   "",
+		Confidence:      0.9,
+	}
+
+	result := PreviewProposalForSegment(segment, proposal, ReplacementPolicyRequireUnique)
+	if !result.Applicable {
+		t.Fatalf("expected applicable preview, got skip reason %q", result.SkipReason)
+	}
+	if result.CorrectedSegmentText != "hello" {
+		t.Fatalf("unexpected corrected text: %q", result.CorrectedSegmentText)
+	}
+}
+
+func TestPreviewProposalForSegmentRejectsEmptyResultingSegment(t *testing.T) {
+	segment := &schema.Segment{ID: 8, Text: "uh"}
+	proposal := CorrectionProposal{
+		TargetSegmentID: 8,
+		OriginalText:    "uh",
+		CorrectedText:   "",
+		Confidence:      0.9,
+	}
+
+	result := PreviewProposalForSegment(segment, proposal, ReplacementPolicyRequireUnique)
+	if result.Applicable {
+		t.Fatal("expected non-applicable preview")
+	}
+	if result.SkipReason != SkipReasonEmptyResultingText {
+		t.Fatalf("expected skip reason %q, got %q", SkipReasonEmptyResultingText, result.SkipReason)
+	}
+}
+
 func TestPreviewProposalForSegmentPreservesInputSegment(t *testing.T) {
 	segment := &schema.Segment{ID: 9, Speaker: "A", Start: 1.0, End: 2.0, Text: "rank rank"}
 	original := *segment

internal/framework/proposals/proposal.go

@@ -38,9 +38,6 @@ func (p CorrectionProposal) Validate() error {
 	if strings.TrimSpace(p.OriginalText) == "" {
 		return fmt.Errorf("proposal original_text must not be empty")
 	}
-	if strings.TrimSpace(p.CorrectedText) == "" {
-		return fmt.Errorf("proposal corrected_text must not be empty")
-	}
 	if p.Confidence < 0.0 || p.Confidence > 1.0 {
 		return fmt.Errorf("proposal confidence must be between 0.0 and 1.0")
 	}

internal/framework/proposals/proposal_test.go

@@ -35,7 +35,7 @@ func TestCorrectionProposalValidate_InvalidEmptyOriginalText(t *testing.T) {
 	}
 }
 
-func TestCorrectionProposalValidate_InvalidEmptyCorrectedText(t *testing.T) {
+func TestCorrectionProposalValidate_AllowsEmptyCorrectedText(t *testing.T) {
 	proposal := CorrectionProposal{
 		TargetSegmentID: 42,
 		OriginalText:    "gestures",
@@ -43,12 +43,8 @@ func TestCorrectionProposalValidate_InvalidEmptyCorrectedText(t *testing.T) {
 		Confidence:      0.95,
 	}
 
-	err := proposal.Validate()
-	if err == nil {
-		t.Fatal("expected validation error, got nil")
-	}
-	if err.Error() != "proposal corrected_text must not be empty" {
-		t.Fatalf("unexpected error: %v", err)
+	if err := proposal.Validate(); err != nil {
+		t.Fatalf("expected empty corrected_text to be allowed, got %v", err)
 	}
 }