Implemented an initial transcript merge stage

internal/speaker/map.go

@@ -0,0 +1,69 @@
+package speaker
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+// Map resolves input file basenames to canonical speaker names.
+type Map struct {
+	inputs map[string]Input
+}
+
+// Input describes one input entry in speakers.yml.
+type Input struct {
+	Speaker string `yaml:"speaker"`
+}
+
+type fileSchema struct {
+	Inputs map[string]Input `yaml:"inputs"`
+}
+
+// LoadMap parses a speakers.yml file.
+func LoadMap(path string) (Map, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return Map{}, err
+	}
+
+	var parsed fileSchema
+	if err := yaml.Unmarshal(data, &parsed); err != nil {
+		return Map{}, fmt.Errorf("parse speaker map %q: %w", path, err)
+	}
+	if len(parsed.Inputs) == 0 {
+		return Map{}, fmt.Errorf("speaker map %q must contain at least one inputs entry", path)
+	}
+
+	inputs := make(map[string]Input, len(parsed.Inputs))
+	for key, input := range parsed.Inputs {
+		basename := filepath.Base(strings.TrimSpace(key))
+		if basename == "." || basename == "" {
+			return Map{}, fmt.Errorf("speaker map %q contains an empty input key", path)
+		}
+		if _, exists := inputs[basename]; exists {
+			return Map{}, fmt.Errorf("speaker map %q contains duplicate basename mapping for %q", path, basename)
+		}
+
+		input.Speaker = strings.TrimSpace(input.Speaker)
+		if input.Speaker == "" {
+			return Map{}, fmt.Errorf("speaker map entry %q must include speaker", basename)
+		}
+		inputs[basename] = input
+	}
+
+	return Map{inputs: inputs}, nil
+}
+
+// SpeakerForSource returns the canonical speaker for a transcript source path.
+func (m Map) SpeakerForSource(source string) (string, error) {
+	basename := filepath.Base(source)
+	input, ok := m.inputs[basename]
+	if !ok {
+		return "", fmt.Errorf("speaker map has no entry for input basename %q", basename)
+	}
+	return input.Speaker, nil
+}