Limit the pre-commit Codex refresh to trailered commits in this worktree

The session store is shared across worktrees, and an unresolved child rollout can cost a bounded fallback scan. Refreshing every live Codex session before every commit made unrelated sessions slow down commits that condense nothing. Only a commit with an Entire-Checkpoint trailer condenses, so refresh only then, and only sessions whose home is this worktree (or unknown).

Also correct the regression test's comment: this fixture's child is a fork, whose usage stays unset by design.