cache: git-tracked build cache — 16 packages, survives make clean + clone

Red Bear is a fork/overlay on top of Redox. The upstream build
system wasn't designed for forks — it loses all cached stages on
make clean with no recovery path.

This commit adds a git-tracked build cache:
- local/cache/pkgar/{pkg}/stage.pkgar — per-package cache files
- cache-sync.sh: sync built packages → git-tracked cache
- cache-sync.sh --restore: restore cache → recipe targets
- cache-sync.sh --commit: sync + git commit
- Auto-restore before build, auto-sync after build

Cache survives: make clean, make distclean, git clone, upstream rebase.
Recovery from clean: seconds (restore from git) vs hours (full rebuild).

local/scripts/cache-sync.sh

@@ -0,0 +1,127 @@
+#!/usr/bin/env bash
+# Red Bear OS — Git-Tracked Build Cache
+# Automatically syncs recipe stage.pkgar files to local/cache/pkgar/
+# and commits them to git so the cache survives make clean AND git clone.
+#
+# The cache is organized as: local/cache/pkgar/{pkgname}/stage.pkgar
+# This keeps individual files small enough for git (<100MB each).
+#
+# Usage:
+#   ./local/scripts/cache-sync.sh              # Sync all built packages to cache
+#   ./local/scripts/cache-sync.sh --commit     # Sync + git commit
+#   ./local/scripts/cache-sync.sh --restore    # Restore cache to recipe targets
+#   ./local/scripts/cache-sync.sh --status     # Show cache vs build state
+
+set -euo pipefail
+cd "$(dirname "$0")/../.."
+
+CACHE_ROOT="local/cache/pkgar"
+mkdir -p "${CACHE_ROOT}"
+
+MODE="${1:-}"
+
+if [ "$MODE" = "--status" ]; then
+    echo "=== Red Bear Cache Status ==="
+    cached=0; stale=0; missing=0
+    for pkgar in "${CACHE_ROOT}"/*/stage.pkgar; do
+        [ -f "$pkgar" ] || continue
+        pkg=$(basename "$(dirname "$pkgar")")
+        recipe_dir=$(find recipes -maxdepth 3 -name "$pkg" -type d 2>/dev/null | head -1)
+        if [ -z "$recipe_dir" ]; then
+            echo "  ORPHAN $pkg (no recipe)"
+            stale=$((stale + 1))
+            continue
+        fi
+        target="${recipe_dir}/target/x86_64-unknown-redox/stage.pkgar"
+        if [ -f "$target" ]; then
+            if [ "$pkgar" -nt "$target" ]; then
+                echo "  STALE  $pkg (cache newer than build)"
+                stale=$((stale + 1))
+            else
+                echo "  SYNCED $pkg"
+                cached=$((cached + 1))
+            fi
+        else
+            echo "  CACHED $pkg (no build)"
+            cached=$((cached + 1))
+        fi
+    done
+    # Check built but not cached
+    while IFS= read -r target; do
+        pkg=$(echo "$target" | sed 's|recipes/[^/]*/[^/]*/||; s|/target/.*||')
+        if [ ! -f "${CACHE_ROOT}/${pkg}/stage.pkgar" ]; then
+            size=$(stat -c%s "$target" 2>/dev/null || echo 0)
+            echo "  UNCACHED $pkg ($(numfmt --to=iec $size 2>/dev/null || echo ${size}B))"
+            missing=$((missing + 1))
+        fi
+    done < <(find recipes -name "stage.pkgar" -path "*/target/x86_64-unknown-redox/*" 2>/dev/null | head -100)
+    echo ""
+    echo "Synced: $cached  Stale: $stale  Uncached: $missing"
+    exit 0
+fi
+
+if [ "$MODE" = "--restore" ]; then
+    echo "=== Restoring Cache to Recipes ==="
+    count=0
+    for pkgar in "${CACHE_ROOT}"/*/stage.pkgar; do
+        [ -f "$pkgar" ] || continue
+        pkg=$(basename "$(dirname "$pkgar")")
+        recipe_dir=$(find recipes -maxdepth 4 -name "$pkg" -type d 2>/dev/null | head -1)
+        if [ -z "$recipe_dir" ]; then continue; fi
+        target="${recipe_dir}/target/x86_64-unknown-redox/stage.pkgar"
+        if [ ! -f "$target" ] || [ "$pkgar" -nt "$target" ]; then
+            mkdir -p "$(dirname "$target")"
+            cp "$pkgar" "$target"
+            count=$((count + 1))
+        fi
+    done
+    echo "Restored $count packages"
+    exit 0
+fi
+
+# Default: --sync mode
+echo "=== Syncing Build Cache ==="
+synced=0
+while IFS= read -r target; do
+    pkg_path="${target%/target/x86_64-unknown-redox/stage.pkgar}"
+    # Extract package name: recipes/{category}/{name}/target/... → {name}
+    pkg=$(basename "$pkg_path")
+    [ -z "$pkg" ] && continue
+    
+    cache_dir="${CACHE_ROOT}/${pkg}"
+    cache_file="${cache_dir}/stage.pkgar"
+    
+    # Only copy if build is newer
+    if [ -f "$cache_file" ] && [ ! "$target" -nt "$cache_file" ]; then
+        continue
+    fi
+    
+    mkdir -p "$cache_dir"
+    cp "$target" "$cache_file"
+    
+    # Also save auto_deps
+    deps_file="${pkg_path}/target/x86_64-unknown-redox/auto_deps.toml"
+    if [ -f "$deps_file" ]; then
+        cp "$deps_file" "${cache_dir}/auto_deps.toml"
+    fi
+    
+    synced=$((synced + 1))
+done < <(find recipes -name "stage.pkgar" -path "*/target/x86_64-unknown-redox/*" 2>/dev/null)
+
+echo "Synced $synced packages to ${CACHE_ROOT}/"
+
+if [ "$MODE" = "--commit" ] && [ $synced -gt 0 ]; then
+    echo ""
+    echo "=== Committing Cache ==="
+    git add "${CACHE_ROOT}/"
+    
+    # Only commit if there are staged changes
+    if git diff --cached --quiet; then
+        echo "No cache changes to commit"
+    else
+        commit_msg="cache: $(date +%Y-%m-%d) — ${synced} packages"
+        git commit -m "$commit_msg"
+        echo "Committed: $commit_msg"
+        echo "To push: git push"
+    fi
+fi