Implemented an overlap detection module in the postprocessing chain

internal/cli/merge_test.go

@@ -149,6 +149,74 @@ func TestMergeTieBreakOrder(t *testing.T) {
 	}
 }
 
+func TestMergeDetectsOverlapGroups(t *testing.T) {
+	dir := t.TempDir()
+	inputA := writeJSONFile(t, dir, "a.json", `{
+		"segments": [
+			{"start": 1, "end": 5, "text": "alice long"},
+			{"start": 2, "end": 3, "text": "alice nested"}
+		]
+	}`)
+	inputB := writeJSONFile(t, dir, "b.json", `{
+		"segments": [
+			{"start": 4, "end": 6, "text": "bob overlap"}
+		]
+	}`)
+	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", inputB,
+		"--input-file", inputA,
+		"--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 len(transcript.OverlapGroups) != 1 {
+		t.Fatalf("overlap group count = %d, want 1", len(transcript.OverlapGroups))
+	}
+	group := transcript.OverlapGroups[0]
+	if group.ID != 1 {
+		t.Fatalf("group ID = %d, want 1", group.ID)
+	}
+	if group.Start != 1 || group.End != 6 {
+		t.Fatalf("group bounds = %f-%f, want 1-6", group.Start, group.End)
+	}
+	wantRefs := []string{inputA + "#0", inputA + "#1", inputB + "#0"}
+	if !equalStrings(group.Segments, wantRefs) {
+		t.Fatalf("group refs = %v, want %v", group.Segments, wantRefs)
+	}
+	if !equalStrings(group.Speakers, []string{"Alice", "Bob"}) {
+		t.Fatalf("group speakers = %v, want [Alice Bob]", group.Speakers)
+	}
+	if group.Class != "unknown" || group.Resolution != "unresolved" {
+		t.Fatalf("unexpected group class/resolution: %q/%q", group.Class, group.Resolution)
+	}
+	for index, segment := range transcript.Segments {
+		if segment.OverlapGroupID != 1 {
+			t.Fatalf("segment %d overlap group ID = %d, want 1", index, segment.OverlapGroupID)
+		}
+	}
+
+	var rpt report.Report
+	readJSON(t, reportPath, &rpt)
+	if !hasReportEvent(rpt, "postprocessing", "detect-overlaps", "detected 1 overlap group(s)") {
+		t.Fatal("expected detect-overlaps report event")
+	}
+}
+
 func TestSpeakerMatchingUsesFirstMatchingRuleCaseInsensitive(t *testing.T) {
 	dir := t.TempDir()
 	input := writeJSONFile(t, dir, "2026-04-19-Adam_Rakestraw.json", `{