Implemented a new internal/danglers package with deterministic two-pass dangling-end then dangling-start resolution

README.md

@@ -51,7 +51,7 @@ Global flags:
 | `--output-modules` | No | `json` | Comma-separated output modules. |
 | `--output-schema` | No | `seriatim` | JSON output contract. Allowed values are `seriatim` and `minimal`. |
 | `--preprocessing-modules` | No | `validate-raw,normalize-speakers,trim-text` | Comma-separated preprocessing modules, evaluated in order. |
-| `--postprocessing-modules` | No | `detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,detect-overlaps,autocorrect,assign-ids,validate-output` | Comma-separated postprocessing modules, evaluated in order. |
+| `--postprocessing-modules` | No | `detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,resolve-danglers,detect-overlaps,autocorrect,assign-ids,validate-output` | Comma-separated postprocessing modules, evaluated in order. |
 | `--coalesce-gap` | No | `3.0` | Maximum same-speaker gap in seconds for `coalesce`; also used as the `resolve-overlaps` context window. Must be a non-negative float. |
 
 Environment variables:
@@ -169,7 +169,7 @@ The default `seriatim` schema uses the full seriatim envelope:
     "input_reader": "json-files",
     "input_files": ["eric.json", "mike.json"],
     "preprocessing_modules": ["validate-raw", "normalize-speakers", "trim-text"],
-    "postprocessing_modules": ["detect-overlaps", "resolve-overlaps", "backchannel", "filler", "coalesce", "detect-overlaps", "autocorrect", "assign-ids", "validate-output"],
+    "postprocessing_modules": ["detect-overlaps", "resolve-overlaps", "backchannel", "filler", "coalesce", "resolve-danglers", "detect-overlaps", "autocorrect", "assign-ids", "validate-output"],
     "output_modules": ["json"]
   },
   "segments": [
@@ -265,7 +265,7 @@ Overlap behavior:
 
 ## Overlap Resolution
 
-The default postprocessing pipeline runs `detect-overlaps`, then `resolve-overlaps`, then `backchannel`, then `filler`, then `coalesce`, then a second `detect-overlaps` pass.
+The default postprocessing pipeline runs `detect-overlaps`, then `resolve-overlaps`, then `backchannel`, then `filler`, then `coalesce`, then `resolve-danglers`, then a second `detect-overlaps` pass.
 
 For each detected overlap group, `resolve-overlaps` uses preserved WhisperX word timing to build smaller word-run replacement segments:
 
@@ -311,12 +311,21 @@ Filler matching is case-insensitive, ignores punctuation for matching and word-c
 
 ## Coalescing
 
-The default pipeline runs `coalesce` before the second overlap detection pass. It merges adjacent same-speaker segments in the transcript's current order when `next.start - current.end <= --coalesce-gap`.
+The default pipeline runs `coalesce` before `resolve-danglers` and the second overlap detection pass. It merges adjacent same-speaker segments in the transcript's current order when `next.start - current.end <= --coalesce-gap`.
 
 Coalesced segments use `source_ref` values such as `coalesce:1`, include `derived_from`, and omit `source_segment_index`.
 
 Different-speaker backchannel and filler segments do not block coalescing of surrounding same-speaker segments. Same-speaker backchannel and filler segments are merged normally when they are within `--coalesce-gap`. When same-speaker segments are coalesced, any `backchannel` or `filler` category from the merged inputs is dropped from the coalesced segment.
 
+## Dangler Resolution
+
+The default pipeline runs `resolve-danglers` after `coalesce` and before the second overlap detection pass. It repairs short derived fragments when they share provenance with a nearby segment:
+
+- Dangling-end fragments have no more than two words and end in punctuation.
+- Dangling-start fragments have no more than two words.
+- Matching uses any shared `derived_from` value.
+- Merged segments use `source_ref` values such as `resolve-danglers:1`, keep the target segment's transcript position, and union `derived_from`.
+
 ## Autocorrect
 
 Autocorrect is included in the default postprocessing pipeline. If `--autocorrect` is omitted, the module leaves transcript text unchanged and records a skip event in the optional report.

architecture.md

@@ -146,7 +146,7 @@ The postprocessing stage applies zero or more modules to the merged transcript.
 Postprocessing modules are selected at runtime with a comma-separated list of canonical module names:
 
 ```text
---postprocessing-modules detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,detect-overlaps,autocorrect,assign-ids,validate-output
+--postprocessing-modules detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,resolve-danglers,detect-overlaps,autocorrect,assign-ids,validate-output
 ```
 
 Modules run in the exact order provided. Unknown module names are configuration errors.
@@ -214,7 +214,7 @@ seriatim merge \
   --speakers speakers.yml \
   --autocorrect autocorrect.yml \
   --preprocessing-modules validate-raw,normalize-speakers,trim-text \
-  --postprocessing-modules detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,detect-overlaps,autocorrect,assign-ids,validate-output \
+  --postprocessing-modules detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,resolve-danglers,detect-overlaps,autocorrect,assign-ids,validate-output \
   --output-modules json \
   --output-schema seriatim \
   --output-file merged.json \
@@ -435,7 +435,7 @@ validate-raw,normalize-speakers,trim-text
 Recommended default postprocessing modules:
 
 ```text
-detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,detect-overlaps,autocorrect,assign-ids,validate-output
+detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,resolve-danglers,detect-overlaps,autocorrect,assign-ids,validate-output
 ```
 
 The default output module is:

internal/builtin/postprocess.go

@@ -9,6 +9,7 @@ import (
 	"gitea.maximumdirect.net/eric/seriatim/internal/backchannel"
 	"gitea.maximumdirect.net/eric/seriatim/internal/coalesce"
 	"gitea.maximumdirect.net/eric/seriatim/internal/config"
+	"gitea.maximumdirect.net/eric/seriatim/internal/danglers"
 	"gitea.maximumdirect.net/eric/seriatim/internal/filler"
 	"gitea.maximumdirect.net/eric/seriatim/internal/model"
 	"gitea.maximumdirect.net/eric/seriatim/internal/overlap"
@@ -169,6 +170,27 @@ func (coalescePostprocessor) Process(ctx context.Context, in model.MergedTranscr
 	}, nil
 }
 
+type resolveDanglersPostprocessor struct{}
+
+func (resolveDanglersPostprocessor) Name() string {
+	return "resolve-danglers"
+}
+
+func (resolveDanglersPostprocessor) Process(ctx context.Context, in model.MergedTranscript, cfg config.Config) (model.MergedTranscript, []report.Event, error) {
+	if err := ctx.Err(); err != nil {
+		return model.MergedTranscript{}, nil, err
+	}
+
+	out, summary := danglers.Apply(in)
+	return out, []report.Event{
+		report.Info(
+			"postprocessing",
+			"resolve-danglers",
+			fmt.Sprintf("merged %d dangling segment(s) into %d target segment(s)", summary.DanglersMerged, summary.TargetsChanged),
+		),
+	}, nil
+}
+
 type autocorrectPostprocessor struct{}
 
 func (autocorrectPostprocessor) Name() string {

internal/builtin/registry.go

@@ -16,6 +16,7 @@ func NewRegistry() *pipeline.Registry {
 	registry.RegisterPostprocessor(backchannelPostprocessor{})
 	registry.RegisterPostprocessor(fillerPostprocessor{})
 	registry.RegisterPostprocessor(coalescePostprocessor{})
+	registry.RegisterPostprocessor(resolveDanglersPostprocessor{})
 	registry.RegisterPostprocessor(assignIDs{})
 	registry.RegisterPostprocessor(validateOutput{})
 	registry.RegisterPostprocessor(autocorrectPostprocessor{})

internal/cli/merge_test.go

@@ -95,6 +95,7 @@ func TestMergeWritesMergedOutputAndReport(t *testing.T) {
 		"resolve-overlaps",
 		"backchannel",
 		"filler",
+		"resolve-danglers",
 		"coalesce",
 		"detect-overlaps",
 		"autocorrect",
@@ -701,6 +702,128 @@ func TestMergeCoalesceGapOverridePreventsMerge(t *testing.T) {
 	}
 }
 
+func TestMergeResolveDanglersMergesDanglingEnd(t *testing.T) {
+	dir := t.TempDir()
+	inputA := writeJSONFile(t, dir, "a.json", `{
+		"segments": [
+			{
+				"start": 1,
+				"end": 4,
+				"text": "main tail.",
+				"words": [
+					{"word": "main", "start": 1, "end": 1.1},
+					{"word": "tail.", "start": 3, "end": 3.1}
+				]
+			}
+		]
+	}`)
+	inputB := writeJSONFile(t, dir, "b.json", `{
+		"segments": [
+			{
+				"start": 1.5,
+				"end": 2,
+				"text": "interruption",
+				"words": [
+					{"word": "interruption", "start": 1.5, "end": 2}
+				]
+			}
+		]
+	}`)
+	speakers := writeYAMLFile(t, dir, "speakers.yml", `match:
+  - speaker: Alice
+    match: ["a.json"]
+  - speaker: Bob
+    match: ["b.json"]
+`)
+	output := filepath.Join(dir, "merged.json")
+	reportPath := filepath.Join(dir, "report.json")
+
+	err := executeMerge(
+		"--input-file", inputA,
+		"--input-file", inputB,
+		"--speakers", speakers,
+		"--output-file", output,
+		"--report-file", reportPath,
+	)
+	if err != nil {
+		t.Fatalf("merge failed: %v", err)
+	}
+
+	var transcript model.FinalTranscript
+	readJSON(t, output, &transcript)
+	if transcript.Segments[0].Speaker != "Alice" || transcript.Segments[0].Text != "main tail." {
+		t.Fatalf("first segment = %#v, want Alice merged dangling end", transcript.Segments[0])
+	}
+	if transcript.Segments[0].ID != 1 || transcript.Segments[1].ID != 2 {
+		t.Fatalf("ids not sequential after resolve-danglers: %#v", transcript.Segments)
+	}
+
+	var rpt report.Report
+	readJSON(t, reportPath, &rpt)
+	if !hasReportEvent(rpt, "postprocessing", "resolve-danglers", "merged 1 dangling segment(s) into 1 target segment(s)") {
+		t.Fatal("expected resolve-danglers report event")
+	}
+}
+
+func TestMergeResolveDanglersMergesDanglingStart(t *testing.T) {
+	dir := t.TempDir()
+	inputA := writeJSONFile(t, dir, "a.json", `{
+		"segments": [
+			{
+				"start": 1,
+				"end": 4,
+				"text": "start target words",
+				"words": [
+					{"word": "start", "start": 1, "end": 1.1},
+					{"word": "target", "start": 3, "end": 3.1},
+					{"word": "words", "start": 3.2, "end": 3.3}
+				]
+			}
+		]
+	}`)
+	inputB := writeJSONFile(t, dir, "b.json", `{
+		"segments": [
+			{
+				"start": 1.5,
+				"end": 2,
+				"text": "interruption",
+				"words": [
+					{"word": "interruption", "start": 1.5, "end": 2}
+				]
+			}
+		]
+	}`)
+	speakers := writeYAMLFile(t, dir, "speakers.yml", `match:
+  - speaker: Alice
+    match: ["a.json"]
+  - speaker: Bob
+    match: ["b.json"]
+`)
+	output := filepath.Join(dir, "merged.json")
+
+	err := executeMerge(
+		"--input-file", inputA,
+		"--input-file", inputB,
+		"--speakers", speakers,
+		"--output-file", output,
+	)
+	if err != nil {
+		t.Fatalf("merge failed: %v", err)
+	}
+
+	var transcript model.FinalTranscript
+	readJSON(t, output, &transcript)
+	found := false
+	for _, segment := range transcript.Segments {
+		if segment.Speaker == "Alice" && segment.Text == "start target words" {
+			found = true
+		}
+	}
+	if !found {
+		t.Fatalf("expected resolved dangling start in output, got %#v", transcript.Segments)
+	}
+}
+
 func TestMergeTagsBackchannelSegments(t *testing.T) {
 	dir := t.TempDir()
 	input := writeJSONFile(t, dir, "input.json", `{

internal/config/config.go

@@ -15,7 +15,7 @@ const (
 	DefaultOutputModules          = "json"
 	DefaultOutputSchema           = OutputSchemaSeriatim
 	DefaultPreprocessingModules   = "validate-raw,normalize-speakers,trim-text"
-	DefaultPostprocessingModules  = "detect-overlaps,resolve-overlaps,backchannel,filler,coalesce,detect-overlaps,autocorrect,assign-ids,validate-output"
+	DefaultPostprocessingModules  = "detect-overlaps,resolve-overlaps,backchannel,filler,resolve-danglers,coalesce,detect-overlaps,autocorrect,assign-ids,validate-output"
 	DefaultOverlapWordRunGap      = 0.75
 	DefaultWordRunReorderWindow   = 1.0
 	DefaultCoalesceGap            = 3.0

internal/danglers/danglers.go

@@ -0,0 +1,261 @@
+package danglers
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+
+	"gitea.maximumdirect.net/eric/seriatim/internal/model"
+)
+
+// Summary records deterministic counters for a resolve-danglers pass.
+type Summary struct {
+	DanglersMerged int
+	TargetsChanged int
+}
+
+// Apply merges tiny derived fragments back into matching provenance targets.
+func Apply(in model.MergedTranscript) (model.MergedTranscript, Summary) {
+	if len(in.Segments) < 2 {
+		return in, Summary{}
+	}
+
+	afterEnds, endSummary := resolveDanglingEnds(in)
+	afterStarts, startSummary := resolveDanglingStarts(afterEnds)
+	return afterStarts, Summary{
+		DanglersMerged: endSummary.DanglersMerged + startSummary.DanglersMerged,
+		TargetsChanged: countResolvedTargets(afterStarts),
+	}
+}
+
+func countResolvedTargets(in model.MergedTranscript) int {
+	count := 0
+	for _, segment := range in.Segments {
+		if strings.HasPrefix(segment.SourceRef, "resolve-danglers:") {
+			count++
+		}
+	}
+	return count
+}
+
+func resolveDanglingEnds(in model.MergedTranscript) (model.MergedTranscript, Summary) {
+	consumed := make([]bool, len(in.Segments))
+	builders := make(map[int]*builder)
+	merged := 0
+
+	for index, segment := range in.Segments {
+		if consumed[index] || !isDanglingEnd(segment) {
+			continue
+		}
+		target := nearestPriorMatch(in.Segments, consumed, index)
+		if target < 0 {
+			continue
+		}
+		builderFor(builders, target, in.Segments[target]).appendEnd(segment)
+		consumed[index] = true
+		merged++
+	}
+
+	return buildResult(in, consumed, builders, merged)
+}
+
+func resolveDanglingStarts(in model.MergedTranscript) (model.MergedTranscript, Summary) {
+	consumed := make([]bool, len(in.Segments))
+	builders := make(map[int]*builder)
+	merged := 0
+
+	for index, segment := range in.Segments {
+		if consumed[index] || !isDanglingStart(segment) {
+			continue
+		}
+		target := nearestSubsequentMatch(in.Segments, consumed, index)
+		if target < 0 {
+			continue
+		}
+		builderFor(builders, target, in.Segments[target]).prependStart(segment)
+		consumed[index] = true
+		merged++
+	}
+
+	return buildResult(in, consumed, builders, merged)
+}
+
+func buildResult(in model.MergedTranscript, consumed []bool, builders map[int]*builder, merged int) (model.MergedTranscript, Summary) {
+	if merged == 0 {
+		return in, Summary{}
+	}
+
+	builderIDs := make([]int, 0, len(builders))
+	for index := range builders {
+		builderIDs = append(builderIDs, index)
+	}
+	sort.Ints(builderIDs)
+	for id, index := range builderIDs {
+		builders[index].sourceRef = fmt.Sprintf("resolve-danglers:%d", id+1)
+	}
+
+	out := model.MergedTranscript{
+		Segments:      make([]model.Segment, 0, len(in.Segments)-merged),
+		OverlapGroups: in.OverlapGroups,
+	}
+	for index, segment := range in.Segments {
+		if consumed[index] {
+			continue
+		}
+		if builder, exists := builders[index]; exists {
+			out.Segments = append(out.Segments, builder.segment())
+			continue
+		}
+		out.Segments = append(out.Segments, segment)
+	}
+
+	return out, Summary{
+		DanglersMerged: merged,
+		TargetsChanged: len(builders),
+	}
+}
+
+type builder struct {
+	target    model.Segment
+	prefixes  []model.Segment
+	suffixes  []model.Segment
+	sourceRef string
+}
+
+func builderFor(builders map[int]*builder, index int, target model.Segment) *builder {
+	if existing, exists := builders[index]; exists {
+		return existing
+	}
+	builders[index] = &builder{target: target}
+	return builders[index]
+}
+
+func (b *builder) appendEnd(segment model.Segment) {
+	b.suffixes = append(b.suffixes, segment)
+}
+
+func (b *builder) prependStart(segment model.Segment) {
+	b.prefixes = append(b.prefixes, segment)
+}
+
+func (b builder) segment() model.Segment {
+	parts := make([]model.Segment, 0, len(b.prefixes)+1+len(b.suffixes))
+	for index := len(b.prefixes) - 1; index >= 0; index-- {
+		parts = append(parts, b.prefixes[index])
+	}
+	parts = append(parts, b.target)
+	parts = append(parts, b.suffixes...)
+
+	merged := model.Segment{
+		Source:      parts[0].Source,
+		SourceRef:   b.sourceRef,
+		DerivedFrom: unionDerivedFrom(parts),
+		Speaker:     b.target.Speaker,
+		Start:       parts[0].Start,
+		End:         parts[0].End,
+		Categories:  append([]string(nil), b.target.Categories...),
+		Words:       make([]model.Word, 0),
+	}
+
+	text := make([]string, 0, len(parts))
+	for _, part := range parts {
+		if part.Source != merged.Source {
+			merged.Source = "derived"
+		}
+		if part.Start < merged.Start {
+			merged.Start = part.Start
+		}
+		if part.End > merged.End {
+			merged.End = part.End
+		}
+		if trimmed := strings.TrimSpace(part.Text); trimmed != "" {
+			text = append(text, trimmed)
+		}
+		merged.Words = append(merged.Words, part.Words...)
+	}
+	merged.Text = strings.Join(text, " ")
+	return merged
+}
+
+func nearestPriorMatch(segments []model.Segment, consumed []bool, index int) int {
+	for candidate := index - 1; candidate >= 0; candidate-- {
+		if consumed[candidate] {
+			continue
+		}
+		if sharesDerivedFrom(segments[index], segments[candidate]) {
+			return candidate
+		}
+	}
+	return -1
+}
+
+func nearestSubsequentMatch(segments []model.Segment, consumed []bool, index int) int {
+	for candidate := index + 1; candidate < len(segments); candidate++ {
+		if consumed[candidate] {
+			continue
+		}
+		if sharesDerivedFrom(segments[index], segments[candidate]) {
+			return candidate
+		}
+	}
+	return -1
+}
+
+func isDanglingEnd(segment model.Segment) bool {
+	return hasDerivedFrom(segment) && wordCount(segment.Text) <= 2 && endsWithPunctuation(segment.Text)
+}
+
+func isDanglingStart(segment model.Segment) bool {
+	return hasDerivedFrom(segment) && wordCount(segment.Text) <= 2
+}
+
+func hasDerivedFrom(segment model.Segment) bool {
+	return len(segment.DerivedFrom) > 0
+}
+
+func wordCount(text string) int {
+	return len(strings.Fields(strings.TrimSpace(text)))
+}
+
+func endsWithPunctuation(text string) bool {
+	text = strings.TrimSpace(text)
+	if text == "" {
+		return false
+	}
+	r, _ := utf8.DecodeLastRuneInString(text)
+	return r != utf8.RuneError && unicode.IsPunct(r)
+}
+
+func sharesDerivedFrom(left model.Segment, right model.Segment) bool {
+	if len(left.DerivedFrom) == 0 || len(right.DerivedFrom) == 0 {
+		return false
+	}
+	seen := make(map[string]struct{}, len(left.DerivedFrom))
+	for _, ref := range left.DerivedFrom {
+		seen[ref] = struct{}{}
+	}
+	for _, ref := range right.DerivedFrom {
+		if _, exists := seen[ref]; exists {
+			return true
+		}
+	}
+	return false
+}
+
+func unionDerivedFrom(segments []model.Segment) []string {
+	seen := make(map[string]struct{})
+	refs := make([]string, 0)
+	for _, segment := range segments {
+		for _, ref := range segment.DerivedFrom {
+			if _, exists := seen[ref]; exists {
+				continue
+			}
+			seen[ref] = struct{}{}
+			refs = append(refs, ref)
+		}
+	}
+	sort.Strings(refs)
+	return refs
+}

internal/danglers/danglers_test.go

@@ -0,0 +1,178 @@
+package danglers
+
+import (
+	"reflect"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/seriatim/internal/model"
+)
+
+func TestApplyMergesDanglingEndIntoNearestPriorSharedDerivedFrom(t *testing.T) {
+	got, summary := Apply(transcript(
+		segment("a", "Alice", 1, 2, "target", []string{"source#1"}),
+		segment("b", "Bob", 2, 3, "middle", []string{"other#1"}),
+		segment("a", "Alice", 3, 4, "end.", []string{"source#1"}),
+	))
+
+	if summary.DanglersMerged != 1 || summary.TargetsChanged != 1 {
+		t.Fatalf("summary = %#v", summary)
+	}
+	if len(got.Segments) != 2 {
+		t.Fatalf("segment count = %d, want 2", len(got.Segments))
+	}
+	assertSegment(t, got.Segments[0], "resolve-danglers:1", "target end.", 1, 4, []string{"source#1"})
+	if got.Segments[0].SourceSegmentIndex != nil || got.Segments[0].OverlapGroupID != 0 || got.Segments[0].ID != 0 {
+		t.Fatalf("stale fields not cleared: %#v", got.Segments[0])
+	}
+}
+
+func TestApplyMergesDanglingStartIntoNearestSubsequentSharedDerivedFrom(t *testing.T) {
+	got, summary := Apply(transcript(
+		segment("a", "Alice", 1, 2, "start", []string{"source#1"}),
+		segment("b", "Bob", 2, 3, "middle", []string{"other#1"}),
+		segment("a", "Alice", 3, 4, "target", []string{"source#1"}),
+	))
+
+	if summary.DanglersMerged != 1 || summary.TargetsChanged != 1 {
+		t.Fatalf("summary = %#v", summary)
+	}
+	if len(got.Segments) != 2 {
+		t.Fatalf("segment count = %d, want 2", len(got.Segments))
+	}
+	assertSegment(t, got.Segments[1], "resolve-danglers:1", "start target", 1, 4, []string{"source#1"})
+}
+
+func TestApplyUsesAnyDerivedFromIntersection(t *testing.T) {
+	got, _ := Apply(transcript(
+		segment("a", "Alice", 1, 2, "target", []string{"source#1", "source#2"}),
+		segment("a", "Alice", 3, 4, "end.", []string{"source#2", "source#3"}),
+	))
+
+	assertSegment(t, got.Segments[0], "resolve-danglers:1", "target end.", 1, 4, []string{"source#1", "source#2", "source#3"})
+}
+
+func TestApplyDoesNotMergeWithoutSharedProvenance(t *testing.T) {
+	in := transcript(
+		segment("a", "Alice", 1, 2, "target", []string{"source#1"}),
+		segment("a", "Alice", 3, 4, "end.", []string{"source#2"}),
+	)
+
+	got, summary := Apply(in)
+	if summary.DanglersMerged != 0 || !reflect.DeepEqual(got, in) {
+		t.Fatalf("unexpected merge:\ngot  %#v\nwant %#v", got, in)
+	}
+}
+
+func TestApplyDoesNotMergeLongDanglers(t *testing.T) {
+	in := transcript(
+		segment("a", "Alice", 1, 2, "target words here", []string{"source#1"}),
+		segment("a", "Alice", 3, 4, "three word end.", []string{"source#1"}),
+	)
+
+	got, summary := Apply(in)
+	if summary.DanglersMerged != 0 || !reflect.DeepEqual(got, in) {
+		t.Fatalf("unexpected merge:\ngot  %#v\nwant %#v", got, in)
+	}
+}
+
+func TestApplyDanglingEndRequiresPunctuation(t *testing.T) {
+	in := transcript(
+		segment("a", "Alice", 1, 2, "target", []string{"source#1"}),
+		segment("a", "Alice", 3, 4, "end", []string{"source#1"}),
+	)
+
+	resolved, _ := resolveDanglingEnds(in)
+	if !reflect.DeepEqual(resolved, in) {
+		t.Fatalf("punctuation-free end should not merge backward:\ngot  %#v\nwant %#v", resolved, in)
+	}
+}
+
+func TestApplyDanglingStartDoesNotRequirePunctuation(t *testing.T) {
+	got, summary := Apply(transcript(
+		segment("a", "Alice", 1, 2, "start", []string{"source#1"}),
+		segment("a", "Alice", 3, 4, "target words", []string{"source#1"}),
+	))
+
+	if summary.DanglersMerged != 1 {
+		t.Fatalf("summary = %#v", summary)
+	}
+	assertSegment(t, got.Segments[0], "resolve-danglers:1", "start target words", 1, 4, []string{"source#1"})
+}
+
+func TestApplyMergesMultipleDanglersIntoOneTarget(t *testing.T) {
+	got, summary := Apply(transcript(
+		segment("a", "Alice", 1, 2, "prefix", []string{"source#1"}),
+		segment("a", "Alice", 3, 4, "target", []string{"source#1"}),
+		segment("a", "Alice", 5, 6, "tail.", []string{"source#1"}),
+	))
+
+	if summary.DanglersMerged != 2 || summary.TargetsChanged != 1 {
+		t.Fatalf("summary = %#v", summary)
+	}
+	if len(got.Segments) != 1 {
+		t.Fatalf("segment count = %d, want 1", len(got.Segments))
+	}
+	assertSegment(t, got.Segments[0], "resolve-danglers:1", "prefix target tail.", 1, 6, []string{"source#1"})
+}
+
+func TestApplyMergedSegmentShape(t *testing.T) {
+	sourceIndex := 1
+	target := segment("a", "Alice", 2, 3, "target", []string{"a#1"})
+	target.ID = 99
+	target.SourceSegmentIndex = &sourceIndex
+	target.OverlapGroupID = 7
+	target.Categories = []string{"manual"}
+	target.Words = []model.Word{{Text: "target", Start: 2, End: 3, Timed: true}}
+
+	dangler := segment("b", "Alice", 1, 1.5, "start", []string{"a#1", "b#2"})
+	dangler.Categories = []string{"dangler"}
+	dangler.Words = []model.Word{{Text: "start", Start: 1, End: 1.5, Timed: true}}
+
+	got, _ := Apply(transcript(dangler, target))
+	merged := got.Segments[0]
+	if merged.Source != "derived" {
+		t.Fatalf("source = %q, want derived", merged.Source)
+	}
+	if !reflect.DeepEqual(merged.Categories, []string{"manual"}) {
+		t.Fatalf("categories = %v, want target categories only", merged.Categories)
+	}
+	if gotWords := []string{merged.Words[0].Text, merged.Words[1].Text}; !reflect.DeepEqual(gotWords, []string{"start", "target"}) {
+		t.Fatalf("word order = %v", gotWords)
+	}
+	assertSegment(t, merged, "resolve-danglers:1", "start target", 1, 3, []string{"a#1", "b#2"})
+	if merged.ID != 0 || merged.SourceSegmentIndex != nil || merged.OverlapGroupID != 0 {
+		t.Fatalf("stale fields not cleared: %#v", merged)
+	}
+}
+
+func transcript(segments ...model.Segment) model.MergedTranscript {
+	return model.MergedTranscript{Segments: segments}
+}
+
+func segment(source string, speaker string, start float64, end float64, text string, derivedFrom []string) model.Segment {
+	return model.Segment{
+		Source:      source,
+		SourceRef:   source + "-ref",
+		DerivedFrom: append([]string(nil), derivedFrom...),
+		Speaker:     speaker,
+		Start:       start,
+		End:         end,
+		Text:        text,
+	}
+}
+
+func assertSegment(t *testing.T, segment model.Segment, sourceRef string, text string, start float64, end float64, derivedFrom []string) {
+	t.Helper()
+	if segment.SourceRef != sourceRef {
+		t.Fatalf("source_ref = %q, want %q", segment.SourceRef, sourceRef)
+	}
+	if segment.Text != text {
+		t.Fatalf("text = %q, want %q", segment.Text, text)
+	}
+	if segment.Start != start || segment.End != end {
+		t.Fatalf("bounds = %f-%f, want %f-%f", segment.Start, segment.End, start, end)
+	}
+	if !reflect.DeepEqual(segment.DerivedFrom, derivedFrom) {
+		t.Fatalf("derived_from = %v, want %v", segment.DerivedFrom, derivedFrom)
+	}
+}