Add TOML support for formulas (gt-xmyha)

- Add TOML parsing using BurntSushi/toml
- Update formula loader to try .toml first, fall back to .json
- Add `bd formula convert` command for JSON→TOML migration
- Multi-line string support for readable descriptions
- Cache git worktree/reporoot checks for performance

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/formula/parser.go

@@ -7,10 +7,16 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+
+	"github.com/BurntSushi/toml"
 )
 
-// FormulaExt is the file extension for formula files.
-const FormulaExt = ".formula.json"
+// Formula file extensions. TOML is preferred, JSON is legacy fallback.
+const (
+	FormulaExtTOML = ".formula.toml"
+	FormulaExtJSON = ".formula.json"
+	FormulaExt     = FormulaExtJSON // Legacy alias for backwards compatibility
+)
 
 // Parser handles loading and resolving formulas.
 //
@@ -68,6 +74,7 @@ func defaultSearchPaths() []string {
 }
 
 // ParseFile parses a formula from a file path.
+// Detects format from extension: .formula.toml or .formula.json
 func (p *Parser) ParseFile(path string) (*Formula, error) {
 	// Check cache first
 	absPath, err := filepath.Abs(path)
@@ -86,7 +93,13 @@ func (p *Parser) ParseFile(path string) (*Formula, error) {
 		return nil, fmt.Errorf("read %s: %w", path, err)
 	}
 
-	formula, err := p.Parse(data)
+	// Detect format from extension
+	var formula *Formula
+	if strings.HasSuffix(path, FormulaExtTOML) {
+		formula, err = p.ParseTOML(data)
+	} else {
+		formula, err = p.Parse(data)
+	}
 	if err != nil {
 		return nil, fmt.Errorf("parse %s: %w", path, err)
 	}
@@ -122,6 +135,24 @@ func (p *Parser) Parse(data []byte) (*Formula, error) {
 	return &formula, nil
 }
 
+// ParseTOML parses a formula from TOML bytes.
+func (p *Parser) ParseTOML(data []byte) (*Formula, error) {
+	var formula Formula
+	if err := toml.Unmarshal(data, &formula); err != nil {
+		return nil, fmt.Errorf("toml: %w", err)
+	}
+
+	// Set defaults
+	if formula.Version == 0 {
+		formula.Version = 1
+	}
+	if formula.Type == "" {
+		formula.Type = TypeWorkflow
+	}
+
+	return &formula, nil
+}
+
 // Resolve fully resolves a formula, processing extends and expansions.
 // Returns a new formula with all inheritance applied.
 func (p *Parser) Resolve(formula *Formula) (*Formula, error) {
@@ -205,18 +236,21 @@ func (p *Parser) Resolve(formula *Formula) (*Formula, error) {
 }
 
 // loadFormula loads a formula by name from search paths.
+// Tries TOML first (.formula.toml), then falls back to JSON (.formula.json).
 func (p *Parser) loadFormula(name string) (*Formula, error) {
 	// Check cache first
 	if cached, ok := p.cache[name]; ok {
 		return cached, nil
 	}
 
-	// Search for the formula file
-	filename := name + FormulaExt
+	// Search for the formula file - try TOML first, then JSON
+	extensions := []string{FormulaExtTOML, FormulaExtJSON}
 	for _, dir := range p.searchPaths {
-		path := filepath.Join(dir, filename)
-		if _, err := os.Stat(path); err == nil {
-			return p.ParseFile(path)
+		for _, ext := range extensions {
+			path := filepath.Join(dir, name+ext)
+			if _, err := os.Stat(path); err == nil {
+				return p.ParseFile(path)
+			}
 		}
 	}