Wave-assembled from PR #3936 by @dovstern. Conflict resolution: kept master's
resolveRepoRoot() block AND the PR's exported currentBranch in
src/core/brain-repo-durability.ts. Adaptation: the new serial test now writes
the simulated push log under $GBRAIN_HOME/.gbrain (CX2-8 parent-dir semantics
landed on master after the PR's base).
Co-Authored-By: Dov Stern <dovstern@users.noreply.github.com>