feat(06-02): create Go→TypeScript event constant codegen tool

- Add backend/events/cmd/genevents/main.go using go/ast for deterministic output
- Add //go:generate directive to backend/events/events.go
- Generate frontend/src/events.ts with all 21 constants including LibraryConfigChanged
- Atomic file writes via temp file + rename
- Comment groups preserved with trailing period stripping

backend/events/cmd/genevents/main.go

@@ -0,0 +1,165 @@
+// Command genevents reads Go event constants from events.go using go/ast
+// and generates the corresponding TypeScript constants file.
+//
+// Usage:
+//
+//	go run ./cmd/genevents -source events.go -output ../../frontend/src/events.ts
+package main
+
+import (
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func main() {
+	source := flag.String("source", "events.go", "path to Go events source file")
+	output := flag.String("output", "", "path to TypeScript output file (stdout if empty)")
+	flag.Parse()
+
+	consts, err := parseEvents(*source)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "genevents: %v\n", err)
+		os.Exit(1)
+	}
+
+	ts := generateTypeScript(consts)
+
+	if *output == "" || *output == "/dev/stdout" {
+		fmt.Print(ts)
+		return
+	}
+
+	if err := writeAtomic(*output, ts); err != nil {
+		fmt.Fprintf(os.Stderr, "genevents: write %s: %v\n", *output, err)
+		os.Exit(1)
+	}
+}
+
+// constGroup holds a block of related constants with its doc comment.
+type constGroup struct {
+	Comment string // doc comment text (empty if none)
+	Consts  []constEntry
+}
+
+// constEntry holds one constant name and its string value.
+type constEntry struct {
+	Name  string
+	Value string
+}
+
+// parseEvents parses the Go source file and extracts typed string constant
+// groups in declaration order.
+func parseEvents(path string) ([]constGroup, error) {
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, path, nil, parser.ParseComments)
+	if err != nil {
+		return nil, fmt.Errorf("parse %s: %w", path, err)
+	}
+
+	var groups []constGroup
+
+	for _, decl := range f.Decls {
+		gd, ok := decl.(*ast.GenDecl)
+		if !ok || gd.Tok != token.CONST {
+			continue
+		}
+
+		var g constGroup
+
+		// Extract doc comment from the const block.
+		if gd.Doc != nil {
+			g.Comment = cleanComment(gd.Doc.Text())
+		}
+
+		for _, spec := range gd.Specs {
+			vs, ok := spec.(*ast.ValueSpec)
+			if !ok {
+				continue
+			}
+			for i, name := range vs.Names {
+				if i >= len(vs.Values) {
+					continue
+				}
+				bl, ok := vs.Values[i].(*ast.BasicLit)
+				if !ok || bl.Kind != token.STRING {
+					continue
+				}
+				// Strip quotes from the string literal value.
+				val := strings.Trim(bl.Value, `"`)
+				g.Consts = append(g.Consts, constEntry{Name: name.Name, Value: val})
+			}
+		}
+
+		if len(g.Consts) > 0 {
+			groups = append(groups, g)
+		}
+	}
+
+	return groups, nil
+}
+
+// cleanComment trims whitespace and strips trailing periods from Go doc
+// comment text (Go convention uses periods; TypeScript comments typically
+// do not).
+func cleanComment(s string) string {
+	s = strings.TrimSpace(s)
+	s = strings.TrimSuffix(s, ".")
+	return s
+}
+
+// generateTypeScript produces the full TypeScript source from the parsed
+// constant groups.
+func generateTypeScript(groups []constGroup) string {
+	var b strings.Builder
+
+	b.WriteString("// Code generated by genevents from backend/events/events.go. DO NOT EDIT.\n")
+	b.WriteString("\n")
+	b.WriteString("export const Events = {\n")
+
+	for i, g := range groups {
+		if g.Comment != "" {
+			b.WriteString("    // " + g.Comment + "\n")
+		}
+		for _, c := range g.Consts {
+			b.WriteString(fmt.Sprintf("    %s: %q,\n", c.Name, c.Value))
+		}
+		// Blank line between groups, but not after the last one.
+		if i < len(groups)-1 {
+			b.WriteString("\n")
+		}
+	}
+
+	b.WriteString("} as const;\n")
+	b.WriteString("\n")
+	b.WriteString("export type EventName = (typeof Events)[keyof typeof Events];\n")
+
+	return b.String()
+}
+
+// writeAtomic writes data to a temporary file in the same directory as path,
+// then renames it into place for atomic replacement.
+func writeAtomic(path, data string) error {
+	dir := filepath.Dir(path)
+	tmp, err := os.CreateTemp(dir, ".genevents-*.tmp")
+	if err != nil {
+		return err
+	}
+	tmpName := tmp.Name()
+
+	if _, err := tmp.WriteString(data); err != nil {
+		tmp.Close()
+		os.Remove(tmpName)
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		os.Remove(tmpName)
+		return err
+	}
+	return os.Rename(tmpName, path)
+}

backend/events/events.go

@@ -3,6 +3,8 @@
 // the corresponding event names in the TypeScript frontend.
 package events
 
+//go:generate go run ./cmd/genevents -source events.go -output ../../frontend/src/events.ts
+
 // Playback events (backend → frontend push).
 const (
 	PlaybackStateChanged = "PlaybackStateChanged"

frontend/src/events.ts

@@ -1,5 +1,4 @@
-// Centralized event name constants for Wails frontend/backend communication.
+// Code generated by genevents from backend/events/events.go. DO NOT EDIT.
-// These names must match the corresponding event names in the Go backend.
 
 export const Events = {
     // Playback events (backend → frontend push)
@@ -15,6 +14,12 @@ export const Events = {
     QueueModeChanged: "QueueModeChanged",
     QueueTracksModified: "QueueTracksModified",
 
+    // Config events
+    LibraryConfigChanged: "LibraryConfigChanged",
+    ThemeConfigChanged: "ThemeConfigChanged",
+    TrackListConfigChanged: "TrackListConfigChanged",
+    FavoritesConfigChanged: "FavoritesConfigChanged",
+
     // Playlist events
     PlaylistCreated: "PlaylistCreated",
     PlaylistDeleted: "PlaylistDeleted",
@@ -23,11 +28,6 @@ export const Events = {
     PlaylistsRestored: "PlaylistsRestored",
     DefaultPlaylistChanged: "DefaultPlaylistChanged",
 
-    // Config events
-    ThemeConfigChanged: "ThemeConfigChanged",
-    TrackListConfigChanged: "TrackListConfigChanged",
-    FavoritesConfigChanged: "FavoritesConfigChanged",
-
     // Library events
     LibraryScanStarted: "LibraryScanStarted",
     LibraryScanComplete: "LibraryScanComplete",