Fix CI: install git in the Slackware build container before checkout

vbatts/slackware:15.0 ships neither git nor its runtime shared libs
(nghttp2, brotli, cyrus-sasl) or ca-certificates, so actions/checkout
was failing immediately with "base image is missing git/tar". Install
git and its dependencies from Slackware's own official mirror, pinned
by exact filename and verified SHA256, and build the CA bundle so git
can trust HTTPS remotes. Verified end-to-end against the real Gitea
instance (git ls-remote succeeds) in a fresh vbatts/slackware:15.0
container.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/build-packages.yml

@@ -46,8 +46,27 @@ on:
 # pin by digest) if the project standardizes on a different/self-hosted
 # base image. See scripts/ci/setup-slackware-buildenv.sh for how missing
 # build dependencies are bootstrapped on top of whatever this image ships.
+#
+# vbatts/slackware:15.0 ships tar but NOT git (needed by actions/checkout)
+# or any of git's runtime dependencies. The "Install git" step below pulls
+# git and its missing shared libraries from Slackware's own official
+# package mirror, pinned by exact filename + verified SHA256, before
+# actions/checkout runs — see that step for the full dependency chain
+# (found by trial: git needs libnghttp2, which needs nothing extra, but
+# git also dlopens libbrotlidec and libsasl2 for HTTPS transport).
 env:
   SLACKWARE_IMAGE: "vbatts/slackware:15.0"
+  SLACKWARE_MIRROR: "http://slackware.osuosl.org/slackware64-15.0/slackware64"
+  GIT_PKG: "d/git-2.35.1-x86_64-1.txz"
+  GIT_PKG_SHA256: "502a8e921c13a3e89fa121d26e6e376bd927b05e5a2d1039c1bf815ab6ec535d"
+  CA_CERTIFICATES_PKG: "n/ca-certificates-20211216-noarch-1.txz"
+  CA_CERTIFICATES_PKG_SHA256: "e26e8e1371dd5f4f53978cef0449542e7e56b26d1813dcbc546159b551939a91"
+  NGHTTP2_PKG: "n/nghttp2-1.46.0-x86_64-1.txz"
+  NGHTTP2_PKG_SHA256: "cad5c7b38ae424b3f44b707637623f740da45a1d1f9938933dc472f931d2bddc"
+  BROTLI_PKG: "l/brotli-1.0.9-x86_64-7.txz"
+  BROTLI_PKG_SHA256: "f20e995cce0cf5c4f2575f94e87978e6e5f7d3923e847e3bca814e7c324bd474"
+  CYRUS_SASL_PKG: "n/cyrus-sasl-2.1.27-x86_64-7.txz"
+  CYRUS_SASL_PKG_SHA256: "b613130758ec952b8585e03f5174c924bc8bfc6d90aa6c53e7e73a30c6801b68"
 
 jobs:
   build:
@@ -58,10 +77,38 @@ jobs:
     outputs:
       artifact-name: ${{ steps.artifact-name.outputs.value }}
     steps:
-      - name: Install git and tar (needed before actions/checkout can run)
+      - name: Install git (needed before actions/checkout can run)
         run: |
-          (command -v git && command -v tar) || \
-            (echo "!! base image is missing git/tar — see SLACKWARE_IMAGE in this workflow" && exit 1)
+          set -eu
+          command -v tar > /dev/null || (echo "!! base image is missing tar — see SLACKWARE_IMAGE in this workflow" && exit 1)
+
+          cd /tmp
+          for pkg in "$CA_CERTIFICATES_PKG" "$NGHTTP2_PKG" "$BROTLI_PKG" "$CYRUS_SASL_PKG" "$GIT_PKG"; do
+            wget -q --tries=3 "$SLACKWARE_MIRROR/$pkg"
+          done
+          echo "${CA_CERTIFICATES_PKG_SHA256}  $(basename "$CA_CERTIFICATES_PKG")" | sha256sum -c -
+          echo "${NGHTTP2_PKG_SHA256}  $(basename "$NGHTTP2_PKG")" | sha256sum -c -
+          echo "${BROTLI_PKG_SHA256}  $(basename "$BROTLI_PKG")" | sha256sum -c -
+          echo "${CYRUS_SASL_PKG_SHA256}  $(basename "$CYRUS_SASL_PKG")" | sha256sum -c -
+          echo "${GIT_PKG_SHA256}  $(basename "$GIT_PKG")" | sha256sum -c -
+
+          # installpkg has no dependency resolver (unlike slackpkg) — install
+          # git's runtime libs first, then git itself.
+          installpkg "$(basename "$CA_CERTIFICATES_PKG")"
+          installpkg "$(basename "$NGHTTP2_PKG")"
+          installpkg "$(basename "$BROTLI_PKG")"
+          installpkg "$(basename "$CYRUS_SASL_PKG")"
+          installpkg "$(basename "$GIT_PKG")"
+
+          # ca-certificates ships individual certs under
+          # /usr/share/ca-certificates/ — this builds the combined bundle
+          # git needs to actually trust HTTPS remotes (without it, cloning
+          # from a Gitea instance over HTTPS fails cert verification even
+          # though the certs are installed).
+          update-ca-certificates
+          echo "GIT_SSL_CAINFO=/etc/ssl/certs/ca-certificates.crt" >> "$GITHUB_ENV"
+
+          git --version
 
       - uses: actions/checkout@v4