Second layer under #2560's --include-gitignored: a realpath'd ceiling at the
staging dir's parent pushes any git-enumerating collector off the git fast
path (which sees zero files under ~/.gstack's ignore-everything root) onto
its plain FS walk, even on gbrain builds whose flag semantics drift. Ceiling
is realpath'd because git compares canonicalized directories during
discovery — a staging dir reached through a symlink (macOS /var ->
/private/var, symlinked $GSTACK_HOME) otherwise never matches.
Behavioral tests prove discovery stops at the ceiling from the staging dir,
including through a symlinked path, using git itself — no gbrain required.
Mechanism ported from time-attack/gstack (GStack 2).
Co-authored-by: Sina Matian <sina@time-attack.dev>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
