Minimal isolation: git worktree list first-entry != the orchestrator's worktree (gsd-core execute-phase wave-cleanup, #3174 follow-up)

worktree-first-entry-isolation.sh

#!/usr/bin/env bash
# Minimal isolation: `git worktree list`'s first entry is the MAIN checkout,
# not the worktree you are running from. Resolving PRIMARY_WT to the first
# entry therefore mis-pins the orchestrator whenever it runs from a
# non-primary worktree (a per-phase worktree "lane").
set -euo pipefail
tmp=$(mktemp -d); cd "$tmp"
git init -q r && cd r && git commit -q --allow-empty -m init
git worktree add -q ../lane -b lane     # second worktree on branch 'lane'
cd ../lane                              # orchestrator runs from the lane, not the primary
PRIMARY_WT=$(git worktree list --porcelain | awk '/^worktree /{print substr($0,10); exit}')
echo "cwd (orchestrator worktree): $(pwd -P)"
echo "PRIMARY_WT (first-entry):    $(cd "$PRIMARY_WT" && pwd -P)"
# => PRIMARY_WT is .../r (the main checkout), NOT .../lane. execute-phase.md then
#    cd's the orchestrator off its lane; the ORCH_BRANCH == EXPECTED_BRANCH assert
#    fails closed and merge-back is refused.