stack/packages/mosaic/framework/tools/git/mosaic-worktree.sh

#!/usr/bin/env bash
# mosaic-worktree.sh — the only supported way to create and dispose of a git
# worktree on a fleet host.
#
# Why this exists as a helper and not as a rule: the rule already existed, in
# the framework's own words ("Big work → /var/tmp"), and 255 GB accumulated in
# $HOME across 842 directories anyway. Five placement conventions were live on
# one fleet host simultaneously. Every one was a decision an agent had to make,
# and a decision an agent has to make is a decision that drifts.
#
# So this script makes NO placement decision available. The caller supplies a
# branch name. Every path is DERIVED:
#
#   main worktree   <- git worktree list --porcelain (never cwd, which may
#                      itself already be a worktree)
#   REPO_NAME       <- basename of the main worktree
#   REPO_PARENT     <- dirname  of the main worktree
#   WT_ROOT         <- $REPO_PARENT/$REPO_NAME-worktrees
#   SLUG            <- branch with '/' replaced by '-'
#   WT_PATH         <- $WT_ROOT/$SLUG
#
# The derivation puts the worktree on the same filesystem as the object store
# it shares, as a sibling of the repo, under one root per repo. Those are the
# properties that make the checkout cheap and — via `git worktree list` —
# enumerable, which is the only reason automated cleanup can ever be safe.
#
# Usage:
#   mosaic-worktree.sh new <branch> [--from <base>]   create (branch may exist)
#   mosaic-worktree.sh path <branch>                  print derived path, no side effect
#   mosaic-worktree.sh list                           this repo's worktrees + state
#   mosaic-worktree.sh rm <branch> [--force]          remove; refuses to lose work
#   mosaic-worktree.sh gc [--apply]                   report/remove clean+pushed worktrees
#
# `rm` and `gc` refuse to delete a worktree with uncommitted changes or with
# commits absent from every remote. That check is by EVIDENCE, never by size or
# age. --force overrides it and is yours to type deliberately.
#
# Run from anywhere inside the repo, or pass --repo <path>.

set -euo pipefail

die() { printf 'mosaic-worktree: %s\n' "$*" >&2; exit 1; }

REPO_HINT=""
ARGS=()
while [ $# -gt 0 ]; do
  case "$1" in
    --repo) REPO_HINT="${2:-}"; shift 2 ;;
    *) ARGS+=("$1"); shift ;;
  esac
done
set -- "${ARGS[@]+"${ARGS[@]}"}"

CMD="${1:-}"
[ -n "$CMD" ] || die "no command. Try: new | path | list | rm | gc"
shift || true

# ---- mechanical derivation -------------------------------------------------
# The FIRST entry of `git worktree list --porcelain` is always the main
# worktree, regardless of which worktree we are standing in. Deriving from cwd
# would nest worktrees inside worktrees.
resolve_repo() {
  local start="${REPO_HINT:-$PWD}"
  git -C "$start" rev-parse --git-dir >/dev/null 2>&1 \
    || die "not inside a git repository: $start"
  MAIN_WT="$(git -C "$start" worktree list --porcelain | awk '/^worktree /{print substr($0,10); exit}')"
  [ -n "$MAIN_WT" ] || die "could not resolve the main worktree"
  REPO_NAME="$(basename -- "$MAIN_WT")"
  REPO_PARENT="$(dirname -- "$MAIN_WT")"
  WT_ROOT="$REPO_PARENT/$REPO_NAME-worktrees"
}

slugify() { printf '%s' "$1" | tr '/' '-'; }

derive_path() {
  local branch="$1"
  [ -n "$branch" ] || die "branch name required"
  printf '%s/%s' "$WT_ROOT" "$(slugify "$branch")"
}

# A worktree root under $HOME defeats the entire point: wrong filesystem, and
# $HOME is for configuration and state, not work products. Refuse rather than
# silently produce the layout we are trying to eliminate.
assert_not_home() {
  local p="$1" home_real repo_real
  home_real="$(cd "$HOME" && pwd -P)"
  repo_real="$(cd "$(dirname -- "$p")" 2>/dev/null && pwd -P || dirname -- "$p")"
  case "$repo_real/" in
    "$home_real"/*)
      die "refusing: derived path is under \$HOME ($p).
The repo itself lives under \$HOME, so its worktrees would too. Move the repo
to a work filesystem (e.g. /src/$REPO_NAME) and re-run. \$HOME holds
configuration, credentials, state and caches — not checkouts." ;;
  esac
}

# ---- work-loss evidence ----------------------------------------------------
# Two independent questions, both answered from git, neither from size or age:
#   dirty    — anything uncommitted in the tree
#   unpushed — commits reachable from HEAD that no remote ref contains
wt_dirty()    { git -C "$1" status --porcelain 2>/dev/null | head -200 | wc -l; }
wt_unpushed() { git -C "$1" rev-list --count HEAD --not --remotes 2>/dev/null || echo "?"; }

wt_state() {
  local wt="$1" d u
  d="$(wt_dirty "$wt")"; u="$(wt_unpushed "$wt")"
  if [ "$d" -eq 0 ] && [ "$u" = "0" ]; then
    printf 'SAFE\tclean; 0 unpushed'
  else
    printf 'PRESERVE\t%s uncommitted; %s unpushed' "$d" "$u"
  fi
}

# ---- commands --------------------------------------------------------------
cmd_path() { resolve_repo; derive_path "${1:-}"; echo; }

cmd_new() {
  local branch="${1:-}" base=""
  shift || true
  while [ $# -gt 0 ]; do
    case "$1" in --from) base="${2:-}"; shift 2 ;; *) die "unknown flag: $1" ;; esac
  done
  [ -n "$branch" ] || die "usage: mosaic-worktree.sh new <branch> [--from <base>]"

  resolve_repo
  local path; path="$(derive_path "$branch")"
  assert_not_home "$path"

  if [ -e "$path" ]; then
    echo "exists: $path"
    echo "(already checked out — reuse it, or 'rm' it first)"
    return 0
  fi

  mkdir -p "$WT_ROOT"

  # Existing branch -> check it out. New branch -> create from base (default:
  # the remote's default branch if resolvable, else current HEAD).
  if git -C "$MAIN_WT" show-ref --verify --quiet "refs/heads/$branch" \
     || git -C "$MAIN_WT" show-ref --verify --quiet "refs/remotes/origin/$branch"; then
    git -C "$MAIN_WT" worktree add "$path" "$branch"
  else
    if [ -z "$base" ]; then
      base="$(git -C "$MAIN_WT" symbolic-ref --quiet --short refs/remotes/origin/HEAD 2>/dev/null || true)"
      [ -n "$base" ] || base="HEAD"
    fi
    git -C "$MAIN_WT" worktree add -b "$branch" "$path" "$base"
  fi

  cat <<EOF

worktree: $path
branch:   $branch

Removal is part of this task, not a later chore. When the work is pushed:
  mosaic-worktree.sh rm $branch
EOF
}

cmd_list() {
  resolve_repo
  printf 'repo: %s\nroot: %s\n\n' "$MAIN_WT" "$WT_ROOT"
  git -C "$MAIN_WT" worktree list --porcelain \
    | awk '/^worktree /{print substr($0,10)}' \
    | while read -r wt; do
        [ "$wt" = "$MAIN_WT" ] && { printf '%-10s %s (main)\n' "-" "$wt"; continue; }
        printf '%-10s %s\t%s\n' "$(wt_state "$wt" | cut -f1)" "$wt" "$(wt_state "$wt" | cut -f2)"
      done
}

cmd_rm() {
  local branch="${1:-}" force=0
  shift || true
  while [ $# -gt 0 ]; do
    case "$1" in --force) force=1; shift ;; *) die "unknown flag: $1" ;; esac
  done
  [ -n "$branch" ] || die "usage: mosaic-worktree.sh rm <branch> [--force]"

  resolve_repo
  local path; path="$(derive_path "$branch")"
  [ -d "$path" ] || die "no worktree at $path"

  local d u
  d="$(wt_dirty "$path")"; u="$(wt_unpushed "$path")"
  if [ "$force" -eq 0 ] && { [ "$d" -ne 0 ] || [ "$u" != "0" ]; }; then
    die "refusing to remove $path
  uncommitted files: $d
  unpushed commits:  $u
Commit and push first — that is the contract. If this work is genuinely
disposable, re-run with --force."
  fi

  # NB: ${force:+--force} would expand for force=0 too ("0" is non-empty).
  if [ "$force" -eq 1 ]; then
    git -C "$MAIN_WT" worktree remove --force "$path"
  else
    git -C "$MAIN_WT" worktree remove "$path"
  fi
  git -C "$MAIN_WT" worktree prune
  echo "removed: $path"
  rmdir "$WT_ROOT" 2>/dev/null || true
}

cmd_gc() {
  local apply=0
  [ "${1:-}" = "--apply" ] && apply=1
  resolve_repo
  git -C "$MAIN_WT" worktree prune
  git -C "$MAIN_WT" worktree list --porcelain \
    | awk '/^worktree /{print substr($0,10)}' \
    | while read -r wt; do
        [ "$wt" = "$MAIN_WT" ] && continue
        local_state="$(wt_state "$wt")"
        case "$local_state" in
          SAFE*)
            if [ "$apply" -eq 1 ]; then
              git -C "$MAIN_WT" worktree remove "$wt" && echo "removed: $wt"
            else
              echo "reclaimable (clean + fully pushed): $wt"
            fi ;;
          *) echo "preserved: $wt  [$(printf '%s' "$local_state" | cut -f2)]" ;;
        esac
      done
  git -C "$MAIN_WT" worktree prune
  [ "$apply" -eq 1 ] || echo $'\n(report only — re-run with --apply to remove the reclaimable ones)'
}

case "$CMD" in
  new)  cmd_new  "$@" ;;
  path) cmd_path "$@" ;;
  list) cmd_list "$@" ;;
  rm)   cmd_rm   "$@" ;;
  gc)   cmd_gc   "$@" ;;
  -h|--help|help) sed -n '2,40p' "$0" | sed 's/^# \{0,1\}//' ;;
  *) die "unknown command: $CMD (new | path | list | rm | gc)" ;;
esac