Incremental package builds and releases on v* tags (0.8.0)

- build-packages.sh rebuilds a package only when its srcpkgs/ directory
  changed, its binary package is missing, or a dry-run install finds a
  shared library Void no longer provides; DASOS_REBUILD=1 rebuilds all.
  An unchanged `make packages` takes 20 s instead of 17 min on the CI host
- ci/release.sh publishes both ISOs and SHA256SUMS as a Gitea release
  when the workflow runs for a v* tag matching VERSION
- README and TODO updated

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/builder.sh

@@ -18,4 +18,5 @@ exec docker run --rm --privileged \
   --volume "$out/cache/xbps:/var/cache/xbps" \
   --env HOST_UID="$(id -u)" \
   --env HOST_GID="$(id -g)" \
+  --env DASOS_REBUILD \
   "$image" "$@"

scripts/container/build-packages.sh

@@ -34,6 +34,30 @@ XBPS_CHROOT_CMD=uchroot
 XBPS_MAKEJOBS=$(nproc)
 CONF
 
+# A package is rebuilt only when its directory in srcpkgs/ changed since the last
+# build, its binary package is gone, or Void no longer provides a shared library
+# it links to (a soname bump there needs a rebuild here). DASOS_REBUILD=1 rebuilds all.
+stamps=$hostdir/stamps
+mkdir -p "$stamps"
+srchash() {
+  (cd "$vp/srcpkgs/$1" && find . -type f -print0 | sort -z | xargs -0 sha256sum) | sha256sum | cut -d' ' -f1
+}
+# An empty root to dry-run installs into: xbps refuses unresolved shared libraries
+checkroot=$(mktemp -d)
+mkdir -p "$checkroot/var/db/xbps/keys"
+cp -a /var/db/xbps/keys/. "$checkroot/var/db/xbps/keys/"
+voidrepo=$(sed -n 's/^repository=//p' /usr/share/xbps.d/*-repository-main.conf | head -1)
+xbps-install -S -r "$checkroot" -R "$voidrepo" >/dev/null
+up_to_date() {
+  local info version revision
+  [[ ${DASOS_REBUILD:-} != 1 && -f $stamps/$1 && $(< "$stamps/$1") == "$(srchash "$1")" ]] || return 1
+  info=$(as_builder ./xbps-src show "$1")
+  version=$(sed -n 's/^version:[[:space:]]*//p' <<<"$info")
+  revision=$(sed -n 's/^revision:[[:space:]]*//p' <<<"$info")
+  compgen -G "$hostdir/binpkgs/$1-${version}_$revision.*.xbps" >/dev/null || return 1
+  xbps-install -n -y -r "$checkroot" -R "$hostdir/binpkgs" -R "$voidrepo" "$1" >/dev/null 2>&1
+}
+
 names=()
 for dir in /work/srcpkgs/*/; do
   name=$(basename "$dir")
@@ -59,9 +83,16 @@ fi
 # (also as a dependency of another one) would package the stale files
 rm -rf masterdir-x86_64/destdir/*
 for name in "${names[@]}"; do
+  if up_to_date "$name"; then
+    echo "==> $name is up to date"
+    continue
+  fi
   echo "==> Building $name"
   as_builder ./xbps-src -H "$hostdir" -f pkg "$name"
+  srchash "$name" >"$stamps/$name"
 done
+rm -rf "$checkroot"
+chown -R "$HOST_UID:$HOST_GID" "$stamps"
 
 echo "==> Repository: $hostdir/binpkgs"
 ls -1 "$hostdir"/binpkgs/*.xbps