Function resolveGitDir

src/utils/git/gitFilesystem.ts:40–76

(
  startPath?: string,
)

 * Memoized per startPath.
 */
export async function resolveGitDir(
  startPath?: string,
): Promise<string | null> {
  const cwd = resolve(startPath ?? getCwd())
  const cached = resolveGitDirCache.get(cwd)
  if (cached !== undefined) {
    return cached
  }

  const root = findGitRoot(cwd)
  if (!root) {
    resolveGitDirCache.set(cwd, null)
    return null
  }

  const gitPath = join(root, '.git')
  try {
    const st = await stat(gitPath)
    if (st.isFile()) {
      // Worktree or submodule: .git is a file with `gitdir: <path>`
      // Git strips trailing \n and \r (setup.c read_gitfile_gently).
      const content = (await readFile(gitPath, 'utf-8')).trim()
      if (content.startsWith('gitdir:')) {
        const rawDir = content.slice('gitdir:'.length).trim()
        const resolved = resolve(root, rawDir)
        resolveGitDirCache.set(cwd, resolved)
        return resolved
      }
    }
    // Regular repo: .git is a directory
    resolveGitDirCache.set(cwd, gitPath)
    return gitPath
  } catch {
    resolveGitDirCache.set(cwd, null)
    return null
  }
}

// ---------------------------------------------------------------------------
// isSafeRefName — validate ref/branch names read from .git/