The wireup registered a federated source by id, then ran 'gbrain sync --repo $WORKTREE' — which resolves against the brain's DEFAULT source and (on gbrain 0.46.x) rewrites that source's local_path anchor to our worktree. Net effect: the user's primary knowledge source silently repointed at the gstack brain worktree while the just-registered source got zero pages, and pages_synced still reported success. The sync now targets the registered id ('gbrain sync --source $id', the same form the repo's own troubleshooting documents). Because the script's stated floor is gbrain >= 0.18.0 and nothing proves --source exists there, support is probed via 'gbrain sync --help' first: an older gbrain keeps the wrong-but-working --repo call with an upgrade warning instead of converting it into a hard failure. The probe sits after the GSTACK_BRAIN_NO_SYNC early-exit and is unreachable in --probe mode.
Regression tests (fail on v1.68.3.0): a no-skip sync case asserting the call log shows 'sync --source gstack-brain-<id>' and never 'sync --repo', and an old-gbrain fallback case (fake sync --help without --source) asserting --repo plus the upgrade warning.
Fixes#2662
Garry Tan
ffa7b1f452