loadConfig called detectSubRepos(cwd) at up to 3 sites per invocation (root-config
requiresFilesystem migration, workstream-config requiresFilesystem migration, and the
planning.sub_repos filesystem re-sync) — all with the same cwd, yielding identical
results. Introduce a per-call lazy memo (getDetectedSubRepos) so the directory scan
runs at most once per loadConfig call while preserving all conditional logic. Fixes#315.
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>