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+# Package Cache Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add a persistent on-disk package cache so unchanged dependencies are installed from cache instead of rebuilt, while the named target always builds fresh.
+
+**Architecture:** A new `PKG_CACHE` config var points at a local directory laid out as `<cat>/<prog>/<prog>-<ver>-<arch>-<build>_<tag>.txz`, one `.txz` per prog. Three pure helper functions (`cache_decision`, `cache_path`, `cache_store`) hold all cache logic and are unit-tested in `test-logic.sh`. `build_one` gains an `is_target` argument: the target builds fresh and refreshes the cache; deps install from cache on a version match, else build and cache. `update_base` wipes the cache when it patches the base.
+
+**Tech Stack:** Plain bash (single file `sbo-batch-test`), `installpkg`/`upgradepkg` (pkgtools), overlayfs chroot. Self-check in `test-logic.sh` (no VM).
+
+Spec: `docs/superpowers/specs/2026-06-24-package-cache-design.md`.
+
+Note: work directly on master (user preference for this project). Commits are GPG-signed (`-S`). No em dash in any message or comment.
+
+---
+
+### Task 1: Add PKG_CACHE config var and example
+
+**Files:**
+- Modify: `sbo-batch-test` (CONFIG defaults block, around lines 41-50)
+- Modify: `config.example`
+
+- [ ] **Step 1: Add the default in the script CONFIG block**
+
+In `sbo-batch-test`, the CONFIG block sets empty/default vars before sourcing the
+external config. Add `PKG_CACHE` after `LOG_ROOT`. Find:
+
+```sh
+LOG_ROOT="/var/log/sbo-batch-test"
+VERSION="15.0"
+```
+
+Replace with:
+
+```sh
+LOG_ROOT="/var/log/sbo-batch-test"
+
+# Persistent package cache (local disk). Built dependency packages are stored
+# here and reused across runs while their version is unchanged. Empty disables
+# the cache (every package builds fresh). Wiped automatically when the base is
+# patched. Layout mirrors the SBo tree: <cat>/<prog>/<prog>-<ver>-...txz
+PKG_CACHE=""
+
+VERSION="15.0"
+```
+
+- [ ] **Step 2: Document it in config.example**
+
+In `config.example`, after the `LOG_ROOT` block, add:
+
+```sh
+# Persistent package cache. Local disk, survives across runs. Built dependency
+# packages are stored here and reused when their version is unchanged. Wiped
+# automatically when the base is patched. Leave empty to disable caching.
+PKG_CACHE="/var/cache/sbo-batch-test"
+```
+
+- [ ] **Step 3: Verify syntax**
+
+Run: `bash -n sbo-batch-test`
+Expected: no output, exit 0.
+
+- [ ] **Step 4: Verify self-check still passes**
+
+Run: `bash test-logic.sh`
+Expected: ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add sbo-batch-test config.example
+git commit -S -m "Add PKG_CACHE config var (empty = disabled)
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 2: cache_decision (pure) + tests
+
+**Files:**
+- Modify: `sbo-batch-test` (new function, place it just before the "SBo tree lookup" section, i.e. before `find_slackbuild_dir`, around line 302)
+- Test: `test-logic.sh`
+
+`cache_decision <cat> <prog> <version>` globs the prog's cache dir and echoes one
+token: `cached`, `bump:<oldver>:<newver>`, or `new`.
+
+- [ ] **Step 1: Write the failing tests**
+
+In `test-logic.sh`, after the BLOCKED-BY-DEP block and before `# --- result`,
+add:
+
+```bash
+# --- package cache ----------------------------------------------------------
+PKG_CACHE=$(mktemp -d)
+mkc() { mkdir -p "$PKG_CACHE/$1/$2"; : > "$PKG_CACHE/$1/$2/$3"; }
+
+# exact version match -> cached
+mkc net libfoo "libfoo-1.1-x86_64-1_danix.txz"
+[[ "$(cache_decision net libfoo 1.1)" == "cached" ]] && ok "cache hit on version match" || bad "cache_decision should be cached, got [$(cache_decision net libfoo 1.1)]"
+
+# different version cached -> bump:old:new
+[[ "$(cache_decision net libfoo 1.2)" == "bump:1.1:1.2" ]] && ok "cache bump reported" || bad "cache_decision bump wrong, got [$(cache_decision net libfoo 1.2)]"
+
+# nothing cached -> new
+[[ "$(cache_decision net libbar 1.0)" == "new" ]] && ok "cache new for absent prog" || bad "cache_decision should be new, got [$(cache_decision net libbar 1.0)]"
+
+# empty PKG_CACHE disables -> new
+PKG_CACHE_SAVE="$PKG_CACHE"; PKG_CACHE=""
+[[ "$(cache_decision net libfoo 1.1)" == "new" ]] && ok "empty PKG_CACHE disables (new)" || bad "disabled cache should be new, got [$(cache_decision net libfoo 1.1)]"
+PKG_CACHE="$PKG_CACHE_SAVE"
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+Run: `bash test-logic.sh`
+Expected: FAIL lines for the cache checks (function not defined -> empty output mismatches), script exits 1.
+
+- [ ] **Step 3: Implement cache_decision**
+
+In `sbo-batch-test`, just before the `# === SBo tree lookup` section header (before
+`find_slackbuild_dir`), add:
+
+```sh
+# =============================================================================
+# Package cache. Persistent, on-disk store of built packages so unchanged deps
+# are installed from cache instead of rebuilt. Layout mirrors the SBo tree:
+#   $PKG_CACHE/<cat>/<prog>/<prog>-<ver>-<arch>-<build>_<tag>.txz
+# One .txz per prog dir (the latest tested build). Key is prog+version; build
+# number, arch, and tag do not affect a hit. Empty PKG_CACHE disables caching.
+# =============================================================================
+
+# Echo the version field of a cached package filename. <file> is a basename like
+# prog-1.2-x86_64-1_danix.txz; prog may itself contain dashes, so strip the known
+# prog prefix first, then take the field up to the next dash.
+_cache_ver_of() {
+  local prog="$1" base="$2"
+  base="${base#"$prog"-}"     # drop "prog-"
+  echo "${base%%-*}"          # version is up to the next dash
+}
+
+# cache_decision <cat> <prog> <version> -> echoes: cached | bump:OLD:NEW | new
+cache_decision() {
+  local cat="$1" prog="$2" version="$3"
+  [[ -z "$PKG_CACHE" ]] && { echo new; return; }
+  local dir="$PKG_CACHE/$cat/$prog"
+  local f newest=""
+  for f in "$dir/$prog"-*.t?z; do
+    [[ -e "$f" ]] || continue
+    [[ -z "$newest" || "$f" -nt "$newest" ]] && newest="$f"
+  done
+  [[ -z "$newest" ]] && { echo new; return; }
+  local have; have="$(_cache_ver_of "$prog" "$(basename "$newest")")"
+  if [[ "$have" == "$version" ]]; then
+    echo cached
+  else
+    echo "bump:$have:$version"
+  fi
+}
+```
+
+- [ ] **Step 4: Run tests to verify they pass**
+
+Run: `bash test-logic.sh`
+Expected: the four new `ok:` lines, ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add sbo-batch-test test-logic.sh
+git commit -S -m "Add cache_decision + tests
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 3: cache_path + cache_store (pure) + tests
+
+**Files:**
+- Modify: `sbo-batch-test` (append both functions right after `cache_decision`)
+- Test: `test-logic.sh`
+
+`cache_path <cat> <prog> <version>` echoes the cached file for a matching version
+(empty if none). `cache_store <cat> <prog> <src>` clears the prog dir and copies
+`<src>` in (no-op if PKG_CACHE empty).
+
+- [ ] **Step 1: Write the failing tests**
+
+In `test-logic.sh`, append to the package-cache block (after the cache_decision
+tests, before restoring/!cleanup):
+
+```bash
+# cache_path returns the hit file for a matching version
+hit="$(cache_path net libfoo 1.1)"
+[[ "$hit" == "$PKG_CACHE/net/libfoo/libfoo-1.1-x86_64-1_danix.txz" ]] && ok "cache_path returns hit" || bad "cache_path wrong, got [$hit]"
+
+# cache_path empty when version does not match
+[[ -z "$(cache_path net libfoo 9.9)" ]] && ok "cache_path empty on miss" || bad "cache_path should be empty on miss"
+
+# cache_store evicts: prog dir holds exactly the new file
+srctmp=$(mktemp -d); : > "$srctmp/libfoo-1.2-x86_64-1_danix.txz"
+cache_store net libfoo "$srctmp/libfoo-1.2-x86_64-1_danix.txz"
+count=$(find "$PKG_CACHE/net/libfoo" -name '*.t?z' | wc -l)
+[[ "$count" -eq 1 ]] && ok "cache_store evicts to one file" || bad "cache_store left $count files"
+[[ -e "$PKG_CACHE/net/libfoo/libfoo-1.2-x86_64-1_danix.txz" ]] && ok "cache_store stored new file" || bad "cache_store did not store new file"
+rm -rf "$srctmp"
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+Run: `bash test-logic.sh`
+Expected: FAIL lines for cache_path/cache_store (functions not defined), exit 1.
+
+- [ ] **Step 3: Implement cache_path and cache_store**
+
+In `sbo-batch-test`, immediately after the `cache_decision` function, add:
+
+```sh
+# cache_path <cat> <prog> <version> -> echoes the cached .txz path for that
+# version, or nothing. Used to installpkg a cached dep.
+cache_path() {
+  local cat="$1" prog="$2" version="$3"
+  [[ -z "$PKG_CACHE" ]] && return
+  local dir="$PKG_CACHE/$cat/$prog"
+  local f newest=""
+  for f in "$dir/$prog"-*.t?z; do
+    [[ -e "$f" ]] || continue
+    [[ -z "$newest" || "$f" -nt "$newest" ]] && newest="$f"
+  done
+  [[ -z "$newest" ]] && return
+  [[ "$(_cache_ver_of "$prog" "$(basename "$newest")")" == "$version" ]] && echo "$newest"
+}
+
+# cache_store <cat> <prog> <src-txz> -> clear the prog dir, copy src in.
+cache_store() {
+  local cat="$1" prog="$2" src="$3"
+  [[ -z "$PKG_CACHE" ]] && return
+  local dir="$PKG_CACHE/$cat/$prog"
+  mkdir -p "$dir"
+  rm -f "$dir"/*.t?z
+  cp -a "$src" "$dir/"
+}
+```
+
+- [ ] **Step 4: Run tests to verify they pass**
+
+Run: `bash test-logic.sh`
+Expected: the four new `ok:` lines, ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add sbo-batch-test test-logic.sh
+git commit -S -m "Add cache_path + cache_store + tests
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 4: Read each package version for cache lookups (helper)
+
+**Files:**
+- Modify: `sbo-batch-test` (new helper near the other SBo-tree lookups, after `read_requires`)
+
+The build order printing and `build_one` need a package's VERSION from its
+`.info`. Add a small reader so it is not duplicated.
+
+- [ ] **Step 1: Implement version_of**
+
+In `sbo-batch-test`, after the `read_requires` function (SBo tree lookup
+section), add:
+
+```sh
+# Echo the VERSION field from a SlackBuild dir's .info (empty if unreadable).
+# Used as the cache key's version component.
+version_of() {
+  local dir="$1" info="$dir/$(basename "$dir").info"
+  [[ -f "$info" ]] || return
+  # .info lines look like: VERSION="1.2.3"
+  local v; v="$(grep -m1 '^VERSION=' "$info" | cut -d'"' -f2)"
+  echo "$v"
+}
+```
+
+- [ ] **Step 2: Add a test**
+
+In `test-logic.sh`, the `mk` helper writes only REQUIRES. Extend the package-cache
+block with a version_of check using a purpose-built .info:
+
+```bash
+# version_of reads VERSION from .info
+mkdir -p "$T/cat/verpkg"
+printf 'PRGNAM="verpkg"\nVERSION="3.4.5"\nREQUIRES=""\n' > "$T/cat/verpkg/verpkg.info"
+[[ "$(version_of "$T/cat/verpkg")" == "3.4.5" ]] && ok "version_of reads VERSION" || bad "version_of wrong, got [$(version_of "$T/cat/verpkg")]"
+```
+
+- [ ] **Step 3: Run tests to verify pass**
+
+Run: `bash test-logic.sh`
+Expected: new `ok: version_of reads VERSION`, ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add sbo-batch-test test-logic.sh
+git commit -S -m "Add version_of .info reader + test
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 5: Annotate build order with cache outcome (real run + dry-run)
+
+**Files:**
+- Modify: `sbo-batch-test` (`run_target`, dry-run branch around lines 597-605 and real-run order print around lines 607-608)
+
+Show per-package why it will build or reuse, in both dry-run and real run. The
+target is the package whose dir equals the run's target dir (`target_dir` in
+`run_target`).
+
+- [ ] **Step 1: Add a shared annotator helper**
+
+In `sbo-batch-test`, just before `run_target`, add:
+
+```sh
+# Echo a human label for a package's cache outcome, given its SlackBuild dir and
+# whether it is the run's target. Mirrors cache_decision but renders text.
+#   target, build (new) | target, rebuild: A -> B | cached (V) | rebuild: A -> B | build (new)
+cache_label() {
+  local dir="$1" is_target="$2"
+  local cat prog ver dec
+  cat="$(category_of "$dir")"; prog="$(basename "$dir")"; ver="$(version_of "$dir")"
+  dec="$(cache_decision "$cat" "$prog" "$ver")"
+  local label
+  case "$dec" in
+    cached)   label="cached ($ver)" ;;
+    bump:*)   label="rebuild: ${dec#bump:}"; label="${label/:/ -> }" ;;
+    *)        label="build (new)" ;;
+  esac
+  # The target always builds; never show it as plain "cached".
+  if [[ "$is_target" == "1" ]]; then
+    case "$dec" in
+      cached) label="build (cached $ver, rebuilt as target)" ;;
+    esac
+    echo "target, $label"
+  else
+    echo "$label"
+  fi
+}
+```
+
+- [ ] **Step 2: Use it in the dry-run branch**
+
+In `run_target`, replace the dry-run print loop. Find:
+
+```sh
+  if [[ $DRY_RUN -eq 1 ]]; then
+    echo "  build order:"
+    local d
+    for d in "${RESOLVED_ORDER[@]}"; do
+      echo "    $(pkg_key "$d")$([[ "${HAS_README[$d]:-}" == 1 ]] && echo "  [%README%]")"
+      echo "$(pkg_key "$d")" >> "$RUN_DIR/build-order.txt"
+    done
+    return
+  fi
+```
+
+Replace with:
+
+```sh
+  if [[ $DRY_RUN -eq 1 ]]; then
+    echo "  build order:"
+    local d
+    for d in "${RESOLVED_ORDER[@]}"; do
+      local it=0; [[ "$d" == "$target_dir" ]] && it=1
+      local rdm=""; [[ "${HAS_README[$d]:-}" == 1 ]] && rdm="  [%README%]"
+      printf "    %-30s %s%s\n" "$(pkg_key "$d")" "$(cache_label "$d" "$it")" "$rdm"
+      echo "$(pkg_key "$d")" >> "$RUN_DIR/build-order.txt"
+    done
+    return
+  fi
+```
+
+- [ ] **Step 3: Use it in the real-run order print**
+
+In `run_target`, find:
+
+```sh
+  echo "  build order: ${RESOLVED_ORDER[*]##*/}"
+  for d in "${RESOLVED_ORDER[@]}"; do echo "$(pkg_key "$d")" >> "$RUN_DIR/build-order.txt"; done
+```
+
+Replace with:
+
+```sh
+  echo "  build order:"
+  for d in "${RESOLVED_ORDER[@]}"; do
+    local it=0; [[ "$d" == "$target_dir" ]] && it=1
+    printf "    %-30s %s\n" "$(pkg_key "$d")" "$(cache_label "$d" "$it")"
+    echo "$(pkg_key "$d")" >> "$RUN_DIR/build-order.txt"
+  done
+```
+
+- [ ] **Step 4: Verify syntax and self-check**
+
+Run: `bash -n sbo-batch-test && bash test-logic.sh`
+Expected: no syntax error; ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add sbo-batch-test
+git commit -S -m "Annotate build order with cache outcome (run + dry-run)
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 6: Force a controlled OUTPUT path in the build heredoc
+
+**Files:**
+- Modify: `sbo-batch-test` (`build_one` chroot heredoc, lines 500-558)
+
+The harness must control where SlackBuilds write the produced package, instead
+of inheriting `OUTPUT` from the chroot environment. The verified run showed
+`OUTPUT=/repo` leaking in (that is the user's -current repository convention and
+must NOT be used). Force `OUTPUT` to a known overlay path so the build is
+deterministic and the package can be found and cached reliably.
+
+- [ ] **Step 1: Export a fixed OUTPUT inside the heredoc**
+
+In `sbo-batch-test`, find (inside the chroot heredoc, near the top after the
+`. ./$prog.info` line):
+
+```sh
+. ./$prog.info
+
+# Log resolved build context so the overlay never needs to be kept.
+echo "===== sbo-batch-test: $prog ====="
+echo "PRGNAM=\${PRGNAM:-$prog} VERSION=\${VERSION:-?} BUILD=\${BUILD:-?} TAG=\${TAG:-?}"
+echo "uname -m: \$(uname -m)   OUTPUT=\${OUTPUT:-/tmp}"
+```
+
+Replace with:
+
+```sh
+. ./$prog.info
+
+# Force a controlled output dir so the harness, not the SlackBuild's environment,
+# decides where the package lands. Never inherit OUTPUT (the user's -current repo
+# convention sets it to /repo, which must not be touched here).
+export OUTPUT=/sbo-work/output
+mkdir -p "\$OUTPUT"
+
+# Log resolved build context so the overlay never needs to be kept.
+echo "===== sbo-batch-test: $prog ====="
+echo "PRGNAM=\${PRGNAM:-$prog} VERSION=\${VERSION:-?} BUILD=\${BUILD:-?} TAG=\${TAG:-?}"
+echo "uname -m: \$(uname -m)   OUTPUT=\$OUTPUT"
+```
+
+- [ ] **Step 2: Read the produced package from the forced OUTPUT**
+
+In the heredoc's install section, find:
+
+```sh
+# 5. installpkg the resulting package (SlackBuilds write to \${OUTPUT:-/tmp})
+out="\${OUTPUT:-/tmp}"
+pkg="\$(ls -t "\$out"/${prog}-*.t?z 2>/dev/null | head -n1)"
+```
+
+Replace with:
+
+```sh
+# 5. installpkg the resulting package (written to the forced OUTPUT above)
+out="\$OUTPUT"
+pkg="\$(ls -t "\$out"/${prog}-*.t?z 2>/dev/null | head -n1)"
+```
+
+- [ ] **Step 3: Verify syntax and self-check**
+
+Run: `bash -n sbo-batch-test && bash test-logic.sh`
+Expected: no syntax error; ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add sbo-batch-test
+git commit -S -m "Force controlled OUTPUT in build, do not inherit /repo
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 7: Wire cache into build_one (install-from-cache, store-on-build)
+
+**Files:**
+- Modify: `sbo-batch-test` (`build_one` signature + body, lines 479-568; `run_target` call site, line 629)
+
+`build_one` gains a third arg `is_target`. Target -> always build, then store.
+Dep -> on `cached`, installpkg the cached .txz into the overlay and set status
+`CACHED`; otherwise build, then store.
+
+- [ ] **Step 1: Change the run_target call site to pass is_target**
+
+In `run_target`, find:
+
+```sh
+    echo "  building $key ..."
+    if build_one "$tmpdir" "$d"; then
+      echo "  $key: ${ST_STATUS[$key]} (${ST_TIME[$key]}s)"
+    else
+      echo "  $key: ${ST_STATUS[$key]} (${ST_TIME[$key]}s)"
+      failed_progs+=("$prog")
+    fi
+```
+
+Replace with:
+
+```sh
+    local it=0; [[ "$d" == "$target_dir" ]] && it=1
+    echo "  building $key ..."
+    if build_one "$tmpdir" "$d" "$it"; then
+      echo "  $key: ${ST_STATUS[$key]} (${ST_TIME[$key]}s)"
+    else
+      echo "  $key: ${ST_STATUS[$key]} (${ST_TIME[$key]}s)"
+      failed_progs+=("$prog")
+    fi
+```
+
+- [ ] **Step 2: Add is_target arg and the cache-install short-circuit in build_one**
+
+In `sbo-batch-test`, find the start of `build_one`:
+
+```sh
+build_one() {
+  local tmpdir="$1" dir="$2"
+  local c="$tmpdir/chroot"
+  local prog cat key
+  prog="$(basename "$dir")"; cat="$(category_of "$dir")"; key="$cat/$prog"
+  local logf="$RUN_DIR/${cat}_${prog}.log"
+  local start; start=$(date +%s)
+
+  # 1. copy SlackBuild dir into the overlay
+  local workroot="/sbo-work"
+  mkdir -p "$c$workroot"
+  cp -a "$dir" "$c$workroot/$prog"
+
+  # %README% reminder carries through to summary
+  [[ "${HAS_README[$dir]:-}" == "1" ]] && ST_README["$key"]=1
+```
+
+Replace with:
+
+```sh
+build_one() {
+  local tmpdir="$1" dir="$2" is_target="${3:-0}"
+  local c="$tmpdir/chroot"
+  local prog cat key
+  prog="$(basename "$dir")"; cat="$(category_of "$dir")"; key="$cat/$prog"
+  local logf="$RUN_DIR/${cat}_${prog}.log"
+  local start; start=$(date +%s)
+  local version; version="$(version_of "$dir")"
+
+  # %README% reminder carries through to summary
+  [[ "${HAS_README[$dir]:-}" == "1" ]] && ST_README["$key"]=1
+
+  # Dependency with a version-matching cached package: installpkg it into the
+  # overlay and skip the build entirely. The target never takes this path.
+  if [[ "$is_target" != "1" ]]; then
+    local cached; cached="$(cache_path "$cat" "$prog" "$version")"
+    if [[ -n "$cached" ]]; then
+      local workroot="/sbo-work"
+      mkdir -p "$c$workroot"
+      cp -a "$cached" "$c$workroot/"
+      {
+        echo "===== sbo-batch-test: $prog (from cache) ====="
+        echo "cached package: $(basename "$cached")"
+      } >> "$logf"
+      if chroot "$c" /bin/bash -c "installpkg --terse '$workroot/$(basename "$cached")'" >>"$logf" 2>&1; then
+        ST_TIME["$key"]=$(( $(date +%s) - start ))
+        ST_STATUS["$key"]="CACHED"
+        return 0
+      fi
+      # Cache install failed: fall through and build fresh.
+      echo "cache install failed, building fresh" >> "$logf"
+    fi
+  fi
+
+  # 1. copy SlackBuild dir into the overlay
+  local workroot="/sbo-work"
+  mkdir -p "$c$workroot"
+  cp -a "$dir" "$c$workroot/$prog"
+```
+
+- [ ] **Step 3: Store the produced package after a successful build**
+
+In `build_one`, find the tail that reads the status token:
+
+```sh
+  local status="BUILD-FAILED"
+  [[ -f "$statf" ]] && status="$(cat "$statf")"
+  local end; end=$(date +%s)
+  ST_TIME["$key"]=$(( end - start ))
+  ST_STATUS["$key"]="$status"
+  [[ "$status" == "SUCCESS" ]] && return 0
+  ST_REASON["$key"]="see $(basename "$logf")"
+  return 1
+}
+```
+
+Replace with:
+
+```sh
+  local status="BUILD-FAILED"
+  [[ -f "$statf" ]] && status="$(cat "$statf")"
+  local end; end=$(date +%s)
+  ST_TIME["$key"]=$(( end - start ))
+  ST_STATUS["$key"]="$status"
+  if [[ "$status" == "SUCCESS" ]]; then
+    # Copy the produced package out of the overlay into the persistent cache
+    # before teardown, so it can be reused as a dep in this or a later run. The
+    # build wrote to the forced OUTPUT=/sbo-work/output (see the heredoc).
+    local built newest=""
+    for built in "$c"/sbo-work/output/${prog}-*.t?z; do
+      [[ -e "$built" ]] || continue
+      [[ -z "$newest" || "$built" -nt "$newest" ]] && newest="$built"
+    done
+    [[ -n "$newest" ]] && cache_store "$cat" "$prog" "$newest"
+    return 0
+  fi
+  ST_REASON["$key"]="see $(basename "$logf")"
+  return 1
+}
+```
+
+- [ ] **Step 4: Verify syntax and self-check**
+
+Run: `bash -n sbo-batch-test && bash test-logic.sh`
+Expected: no syntax error; ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add sbo-batch-test
+git commit -S -m "Wire cache into build_one: install cached deps, store builds
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 8: CACHED status in summary + cached count
+
+**Files:**
+- Modify: `sbo-batch-test` (`print_summary`, lines 663-698)
+
+`CACHED` must be counted and colored as a non-failure, and the summary line gets
+a cached count.
+
+- [ ] **Step 1: Count and color CACHED**
+
+In `print_summary`, find:
+
+```sh
+  local total=$SECONDS
+  local succ=0 fail=0 blocked=0
+```
+
+Replace with:
+
+```sh
+  local total=$SECONDS
+  local succ=0 fail=0 blocked=0 cached=0
+```
+
+Then find the status case:
+
+```sh
+    case "$st" in
+      SUCCESS) col="$C_GRN"; ((succ++)) ;;
+      BLOCKED-BY-DEP|UNMET-DEP) col="$C_YEL"; ((blocked++)) ;;
+      *) col="$C_RED"; ((fail++)) ;;
+    esac
+```
+
+Replace with:
+
+```sh
+    case "$st" in
+      SUCCESS) col="$C_GRN"; ((succ++)) ;;
+      CACHED)  col="$C_GRN"; ((cached++)) ;;
+      BLOCKED-BY-DEP|UNMET-DEP) col="$C_YEL"; ((blocked++)) ;;
+      *) col="$C_RED"; ((fail++)) ;;
+    esac
+```
+
+- [ ] **Step 2: Add cached to both summary lines**
+
+Find the screen summary line:
+
+```sh
+  printf "%s%d succeeded%s, %s%d failed%s, %s%d blocked%s, total %ss\n" \
+    "$C_GRN" "$succ" "$C_RST" "$C_RED" "$fail" "$C_RST" "$C_YEL" "$blocked" "$C_RST" "$total"
+```
+
+Replace with:
+
+```sh
+  printf "%s%d succeeded%s, %s%d failed%s, %s%d blocked%s, %s%d cached%s, total %ss\n" \
+    "$C_GRN" "$succ" "$C_RST" "$C_RED" "$fail" "$C_RST" "$C_YEL" "$blocked" "$C_RST" \
+    "$C_GRN" "$cached" "$C_RST" "$total"
+```
+
+Find the summary.log line:
+
+```sh
+    echo "$succ succeeded, $fail failed, $blocked blocked, total ${total}s"
+```
+
+Replace with:
+
+```sh
+    echo "$succ succeeded, $fail failed, $blocked blocked, $cached cached, total ${total}s"
+```
+
+- [ ] **Step 3: Verify syntax and self-check**
+
+Run: `bash -n sbo-batch-test && bash test-logic.sh`
+Expected: no syntax error; ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add sbo-batch-test
+git commit -S -m "Report CACHED status and cached count in summary
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 9: Wipe cache on base patch
+
+**Files:**
+- Modify: `sbo-batch-test` (`update_base`, patching branch, lines 290-299)
+
+When `update_base` actually patches, cached deps were built against the old base
+and must be dropped.
+
+- [ ] **Step 1: Add the wipe after patching**
+
+In `update_base`, find:
+
+```sh
+  echo "$head_now" > "$marker"
+  echo "Base patched."
+}
+```
+
+Replace with:
+
+```sh
+  echo "$head_now" > "$marker"
+  # Base changed: cached deps were built against the old base, drop them all.
+  if [[ -n "$PKG_CACHE" && -d "$PKG_CACHE" ]]; then
+    rm -rf "${PKG_CACHE:?}"/*
+    echo "Package cache cleared (base changed)."
+  fi
+  echo "Base patched."
+}
+```
+
+- [ ] **Step 2: Verify syntax and self-check**
+
+Run: `bash -n sbo-batch-test && bash test-logic.sh`
+Expected: no syntax error; ends with `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add sbo-batch-test
+git commit -S -m "Wipe package cache when base is patched
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 10: Update docs (CLAUDE.md, README.md)
+
+**Files:**
+- Modify: `CLAUDE.md` (Status values; Architecture CONFIG entry; Open items/TODO; verified list)
+- Modify: `README.md` (config var list; a cache section)
+
+- [ ] **Step 1: CLAUDE.md status values**
+
+In `CLAUDE.md`, find the Status values block:
+
+```
+`SUCCESS DOWNLOAD-FAILED MD5-MISMATCH BUILD-FAILED INSTALL-FAILED
+BLOCKED-BY-DEP UNMET-DEP`. `%README%` recorded separately as a reminder flag,
+not a status.
+```
+
+Replace with:
+
+```
+`SUCCESS CACHED DOWNLOAD-FAILED MD5-MISMATCH BUILD-FAILED INSTALL-FAILED
+BLOCKED-BY-DEP UNMET-DEP`. `CACHED` = a dependency installed from the persistent
+package cache instead of being rebuilt (target is never CACHED). `%README%`
+recorded separately as a reminder flag, not a status.
+```
+
+- [ ] **Step 2: CLAUDE.md TODO entry (package cache is now done)**
+
+In `CLAUDE.md`, find the deferred package-output cache TODO:
+
+```
+- **Package-output cache** (deferred, user wants it next): keep built `.tgz`
+  outside the overlay, `installpkg` a cached dep instead of rebuilding. Fixes
+  the "shared deps rebuilt per target" cost in category mode. Likely shape: a
+  per-run stash in `$RUN_DIR/pkgcache` keyed `prog-version`, reused across
+  targets within one run. NOT implemented yet.
+```
+
+Replace with:
+
+```
+- **Package cache (DONE).** Persistent `$PKG_CACHE` (config var, empty =
+  disabled), SBo-tree layout `<cat>/<prog>/<prog>-<ver>-...txz`, one .txz per
+  prog. Key = prog+version (build/arch/tag ignored). The named target always
+  builds fresh and refreshes the cache; deps install from cache on a version
+  match (status `CACHED`), else build and cache. Cache wiped when `update_base`
+  patches. Pure `cache_decision`/`cache_path`/`cache_store`/`version_of` covered
+  by `test-logic.sh`. Spec: docs/superpowers/specs/2026-06-24-package-cache-design.md.
+```
+
+- [ ] **Step 3: CLAUDE.md CONFIG architecture entry**
+
+In `CLAUDE.md`, the CONFIG block architecture item lists the vars. Find the
+opening of item 1 (`1. **CONFIG block**`) and add `PKG_CACHE` to the var list at
+its start. Find:
+
+```
+1. **CONFIG block** - empty defaults plus a `source` of the external config
+```
+
+(do not change that line). Then find within the same item the sentence listing
+the block's vars:
+
+```
+   defaults (`SLACKWARE_BASE LOCAL_MIRROR_15 SBO_TREE_ROOTS`) plus
+   `CHROOT_LOCATION=/tmp LOG_ROOT VERSION=15.0`, sources the config if present
+```
+
+Replace with:
+
+```
+   defaults (`SLACKWARE_BASE LOCAL_MIRROR_15 SBO_TREE_ROOTS`) plus
+   `CHROOT_LOCATION=/tmp LOG_ROOT PKG_CACHE='' VERSION=15.0`, sources the config
+   if present
+```
+
+- [ ] **Step 4: CLAUDE.md verified list**
+
+In `CLAUDE.md`, find the "Verified by self-check" item and append the cache
+functions to its coverage list. Find:
+
+```
+  BLOCKED-BY-DEP propagation (`depends_on_failed`, including the transitive
+  one-hop cascade). The check builds a fake SBo tree and sources the script with
+```
+
+Replace with:
+
+```
+  BLOCKED-BY-DEP propagation (`depends_on_failed`, including the transitive
+  one-hop cascade), and the package-cache logic
+  (`cache_decision`/`cache_path`/`cache_store`/`version_of`). The check builds a
+  fake SBo tree and sources the script with
+```
+
+- [ ] **Step 5: README config var + cache section**
+
+In `README.md`, the config prerequisites list documents the externally-set vars.
+After the `SBO_TREE_ROOTS` item (item 3) add a short note, then add a cache
+section after "Populating SLACKWARE_BASE". First, find the populate section's end
+(the paragraph beginning "The base is kept patched automatically"). After that
+paragraph, add:
+
+```markdown
+## Package cache
+
+Set `PKG_CACHE` in your config to a local directory to cache built packages
+across runs (leave empty to disable). Layout mirrors the SBo tree
+(`<category>/<prog>/<prog>-<version>-...txz`), one package per prog.
+
+The named target always builds fresh, it is the package under test. Its
+dependencies are installed from the cache when their version is unchanged
+(reported as `CACHED`), otherwise they are built and cached. A build order line
+shows the outcome per package: `cached (1.1)`, `rebuild: 1.0 -> 1.1`, or
+`build (new)`; `--dry-run` shows the same without building. The whole cache is
+wiped automatically when the base is patched, since cached packages were built
+against the previous base.
+```
+
+- [ ] **Step 6: Verify docs have no em dash and self-check still green**
+
+Run: `grep -n "—" CLAUDE.md README.md || echo "no em dash"`
+Expected: `no em dash`.
+Run: `bash test-logic.sh`
+Expected: `ALL LOGIC CHECKS PASS`.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add CLAUDE.md README.md
+git commit -S -m "Document package cache (CLAUDE.md, README)
+
+Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>"
+```
+
+---
+
+### Task 11: VM verification on buildsystem
+
+**Files:** none (manual verification on the build VM)
+
+This exercises the VM-only paths the self-check cannot reach. Run on
+buildsystem as root, with `PKG_CACHE` set in `/root/.config/sbo-batch-tester/config`.
+
+- [ ] **Step 1: Copy the updated script + example to buildsystem**
+
+Run (from the repo on the workstation):
+`scp sbo-batch-test config.example buildsystem:`
+
+- [ ] **Step 2: Set PKG_CACHE in the buildsystem config**
+
+On buildsystem, add to `/root/.config/sbo-batch-tester/config`:
+`PKG_CACHE="/var/cache/sbo-batch-test"`
+
+- [ ] **Step 3: Dry-run a package with deps**
+
+Run: `sbo-batch-test --dry-run <prog-with-deps>`
+Expected: build order lists each package with `build (new)` (cache empty), target
+line prefixed `target,`.
+
+- [ ] **Step 4: Real run, first time (populates cache)**
+
+Run: `sbo-batch-test <prog-with-deps>`
+Expected: deps build and are cached; target builds. Summary shows
+`N succeeded, 0 failed, 0 blocked, 0 cached`. Check
+`ls -R /var/cache/sbo-batch-test` shows one `.txz` per built prog.
+
+- [ ] **Step 5: Second run reuses cached deps**
+
+Run a DIFFERENT target that shares a dep, or re-run the same target.
+Expected: shared deps report `CACHED`; summary cached count > 0; the target
+still builds fresh (never CACHED). Per-dep log shows `(from cache)`.
+
+- [ ] **Step 6: Confirm eviction on version bump**
+
+Bump a dep's VERSION in its `.info` (or use a package whose version changed),
+run a target needing it.
+Expected: build order shows `rebuild: OLD -> NEW` for that dep; after the run its
+cache dir holds exactly one `.txz` at the new version.
+
+- [ ] **Step 7: Confirm base-patch wipe (optional, only if a patch is pending)**
+
+If the mirror ChangeLog head has advanced, a run triggers `update_base`
+patching, which prints `Package cache cleared (base changed)` and empties
+`/var/cache/sbo-batch-test`. Skip if no patch is pending.
+
+- [ ] **Step 8: Record results**
+
+No commit. Note any deviation (especially the OUTPUT path in Task 6 Step 4: if
+the produced package was not cached, check where the SlackBuild wrote it and
+adjust the store glob in `build_one`).
+
+---
+
+## Notes for the implementer
+
+- Single file `sbo-batch-test`, plain bash. Match the existing comment style and
+  the `ponytail:` convention for deliberate shortcuts.
+- No em dash anywhere (prose, comments, commit messages). Hard rule.
+- Commits are GPG-signed (`-S`). Work on master.
+- `set -uo pipefail` is on: guard array/glob expansions (`[[ -e "$f" ]]` before
+  use), the existing code does this.
+- The self-check sources the script with config set AFTER the source. The cache
+  tests set `PKG_CACHE` after the source too (in the package-cache block).