Added initial segment overlap resolution logic

internal/config/config_test.go

@@ -46,6 +46,86 @@ func TestDuplicateInputFilesFailValidation(t *testing.T) {
 	}
 }
 
+func TestOverlapWordRunGapDefaultsTo075(t *testing.T) {
+	t.Setenv(OverlapWordRunGapEnv, "")
+	dir := t.TempDir()
+	input := writeTempFile(t, dir, "input.json")
+	output := filepath.Join(dir, "merged.json")
+
+	cfg, err := NewMergeConfig(MergeOptions{
+		InputFiles:            []string{input},
+		OutputFile:            output,
+		InputReader:           DefaultInputReader,
+		OutputModules:         DefaultOutputModules,
+		PreprocessingModules:  DefaultPreprocessingModules,
+		PostprocessingModules: DefaultPostprocessingModules,
+	})
+	if err != nil {
+		t.Fatalf("config failed: %v", err)
+	}
+	if cfg.OverlapWordRunGap != DefaultOverlapWordRunGap {
+		t.Fatalf("gap = %f, want %f", cfg.OverlapWordRunGap, DefaultOverlapWordRunGap)
+	}
+}
+
+func TestOverlapWordRunGapUsesValidEnvOverride(t *testing.T) {
+	t.Setenv(OverlapWordRunGapEnv, "1.25")
+	dir := t.TempDir()
+	input := writeTempFile(t, dir, "input.json")
+	output := filepath.Join(dir, "merged.json")
+
+	cfg, err := NewMergeConfig(MergeOptions{
+		InputFiles:            []string{input},
+		OutputFile:            output,
+		InputReader:           DefaultInputReader,
+		OutputModules:         DefaultOutputModules,
+		PreprocessingModules:  DefaultPreprocessingModules,
+		PostprocessingModules: DefaultPostprocessingModules,
+	})
+	if err != nil {
+		t.Fatalf("config failed: %v", err)
+	}
+	if cfg.OverlapWordRunGap != 1.25 {
+		t.Fatalf("gap = %f, want 1.25", cfg.OverlapWordRunGap)
+	}
+}
+
+func TestOverlapWordRunGapRejectsInvalidEnvOverride(t *testing.T) {
+	tests := []struct {
+		name  string
+		value string
+		want  string
+	}{
+		{name: "non-numeric", value: "fast", want: "must be a positive number"},
+		{name: "zero", value: "0", want: "must be positive"},
+		{name: "negative", value: "-0.1", want: "must be positive"},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Setenv(OverlapWordRunGapEnv, test.value)
+			dir := t.TempDir()
+			input := writeTempFile(t, dir, "input.json")
+			output := filepath.Join(dir, "merged.json")
+
+			_, err := NewMergeConfig(MergeOptions{
+				InputFiles:            []string{input},
+				OutputFile:            output,
+				InputReader:           DefaultInputReader,
+				OutputModules:         DefaultOutputModules,
+				PreprocessingModules:  DefaultPreprocessingModules,
+				PostprocessingModules: DefaultPostprocessingModules,
+			})
+			if err == nil {
+				t.Fatal("expected error")
+			}
+			if !strings.Contains(err.Error(), test.want) {
+				t.Fatalf("expected error to contain %q, got %v", test.want, err)
+			}
+		})
+	}
+}
+
 func writeTempFile(t *testing.T, dir string, name string) string {
 	t.Helper()