Function getDiffRef

src/utils/gitDiff.ts:490–502

* Determine the best ref to diff against for a PR-like diff. * Priority: * 1. CLAUDE_CODE_BASE_REF env var (set externally, e.g. by CCR managed containers) * 2. Merge base with the default branch (best guess) * 3. HEAD (fallback if merge-base fails)

(gitRoot: string)

 * 3. HEAD (fallback if merge-base fails)
 */
async function getDiffRef(gitRoot: string): Promise<string> {
  const baseBranch =
    process.env.CLAUDE_CODE_BASE_REF || (await getDefaultBranch())
  const { stdout, code } = await execFileNoThrowWithCwd(
    gitExe(),
    ['--no-optional-locks', 'merge-base', 'HEAD', baseBranch],
    { cwd: gitRoot, timeout: SINGLE_FILE_DIFF_TIMEOUT_MS },
  )
  if (code === 0 && stdout.trim()) {
    return stdout.trim()
  }
  return 'HEAD'
}

async function generateSyntheticDiff(
  gitPath: string,