docs: standardize isolated LLM worktrees (#38)

scripts/worktree-start

@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+  cat <<'EOF'
+usage: scripts/worktree-start [--dry-run] <branch-name> [start-ref]
+
+Create an issue-specific git worktree under branches/<branch-name-with-slashes-replaced>.
+
+Examples:
+  scripts/worktree-start fix/issue-123-example
+  scripts/worktree-start --dry-run review/pr-123-scope-check prgs/master
+EOF
+}
+
+dry_run=0
+if [[ "${1:-}" == "--dry-run" ]]; then
+  dry_run=1
+  shift
+fi
+
+if [[ $# -lt 1 || $# -gt 2 ]]; then
+  usage >&2
+  exit 2
+fi
+
+branch="$1"
+start_ref="${2:-prgs/master}"
+
+script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+repo_root="$(cd "$script_dir/.." && pwd)"
+worktree_name="${branch//\//-}"
+worktree_path="$repo_root/branches/$worktree_name"
+
+if [[ -e "$worktree_path" ]]; then
+  cat >&2 <<EOF
+Refusing to reuse existing branch worktree:
+  $worktree_path
+
+Inspect it manually. Do not overwrite or clean another issue's branch folder
+unless that issue is explicitly assigned and cleanup is part of the task.
+EOF
+  exit 1
+fi
+
+if [[ "$dry_run" -eq 1 ]]; then
+  printf 'repo: %s\n' "$repo_root"
+  printf 'branch: %s\n' "$branch"
+  printf 'start-ref: %s\n' "$start_ref"
+  printf 'worktree: %s\n' "$worktree_path"
+  printf 'commands:\n'
+  printf '  git -C %q fetch prgs --prune\n' "$repo_root"
+  printf '  git -C %q worktree add -b %q %q %q\n' \
+    "$repo_root" "$branch" "$worktree_path" "$start_ref"
+  exit 0
+fi
+
+git -C "$repo_root" fetch prgs --prune
+git -C "$repo_root" worktree add -b "$branch" "$worktree_path" "$start_ref"
+printf '%s\n' "$worktree_path"