hermes -w created the worktree branch from the standalone clone's HEAD, which
lags origin when the clone isn't freshly updated (it's only refreshed by
hermes update, not per session). Every worktree branch then rooted on a stale
base, so the PR diff GitHub computes against current main ballooned with
unrelated changes and the agent had to discover the staleness at push time and
rebase.
_resolve_worktree_base() now fetches and branches from the freshest available
ref: the current branch's upstream if it tracks one (so a deliberate
feature-branch worktree tracks its own remote), else the remote's default
branch (origin/HEAD), else local HEAD as a fail-soft fallback (offline / no
remote / detached). A bogus 'origin/(unknown)' default is guarded, and worktree
creation retries from HEAD if branching off the remote ref fails — so this is
never worse than the old behavior.
Gated by worktree_sync (default true); set worktree_sync: false to keep the
old branch-from-local-HEAD behavior. The resolved base is printed in the
session banner.
This is the follow-up to the #50319 session, where the standalone clone was
213 commits behind origin and the worktree inherited that stale base.
