fix: canonicalize path case on macOS for git worktree operations (GH#880)

bd sync fails with exit status 128 when the daemon is started from a
terminal with different path casing than what git has stored. This
happens on macOS case-insensitive filesystem when directory names
are renamed (e.g., MyProject to myproject) but terminal sessions
retain the old casing.

The fix uses realpath(1) on macOS to get the true filesystem case
when canonicalizing paths:
- CanonicalizePath() now calls realpath on macOS
- git.GetRepoRoot() canonicalizes repoRoot via canonicalizeCase()
- syncbranch.GetRepoRoot() uses utils.CanonicalizePath()

This ensures git worktree paths match exactly, preventing the
exit status 128 errors from git operations.

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

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

Executed-By: beads/crew/dave
Rig: beads
Role: crew

internal/syncbranch/worktree.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/steveyegge/beads/internal/git"
 	"github.com/steveyegge/beads/internal/merge"
+	"github.com/steveyegge/beads/internal/utils"
 )
 
 // CommitResult contains information about a worktree commit operation
@@ -968,7 +969,10 @@ func getRemoteForBranch(ctx context.Context, worktreePath, branch string) string
 
 // GetRepoRoot returns the git repository root directory
 // For worktrees, this returns the main repository root (not the worktree root)
+// The returned path is canonicalized to fix case on case-insensitive filesystems (GH#880)
 func GetRepoRoot(ctx context.Context) (string, error) {
+	var repoRoot string
+
 	// Check if .git is a file (worktree) or directory (regular repo)
 	gitPath := ".git"
 	if info, err := os.Stat(gitPath); err == nil {
@@ -985,7 +989,7 @@ func GetRepoRoot(ctx context.Context) (string, error) {
 				if idx := strings.Index(gitDir, "/worktrees/"); idx > 0 {
 					gitDir = gitDir[:idx]
 				}
-				return filepath.Dir(gitDir), nil
+				repoRoot = filepath.Dir(gitDir)
 			}
 		} else if info.IsDir() {
 			// Regular repo: .git is a directory
@@ -993,17 +997,23 @@ func GetRepoRoot(ctx context.Context) (string, error) {
 			if err != nil {
 				return "", err
 			}
-			return filepath.Dir(absGitPath), nil
+			repoRoot = filepath.Dir(absGitPath)
 		}
 	}
 
-	// Fallback to git command
-	cmd := exec.CommandContext(ctx, "git", "rev-parse", "--show-toplevel")
-	output, err := cmd.Output()
-	if err != nil {
-		return "", fmt.Errorf("not a git repository: %w", err)
+	// Fallback to git command if not determined above
+	if repoRoot == "" {
+		cmd := exec.CommandContext(ctx, "git", "rev-parse", "--show-toplevel")
+		output, err := cmd.Output()
+		if err != nil {
+			return "", fmt.Errorf("not a git repository: %w", err)
+		}
+		repoRoot = strings.TrimSpace(string(output))
 	}
-	return strings.TrimSpace(string(output)), nil
+
+	// Canonicalize path to fix case on macOS/Windows (GH#880)
+	// This is critical for git worktree operations which string-compare paths
+	return utils.CanonicalizePath(repoRoot), nil
 }
 
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