Fix: simplify CI apt caching and mirror handling

Let apt resolve package aliases and missing dependencies while reusing cached downloads. Support Azure mirror replacement in both hosted runners and job containers, and keep timeouts limited to downloads.

Co-Authored-By: Codex <267193182+codex@users.noreply.github.com>

.github/actions/apt-install/action.yml

@@ -1,53 +1,53 @@
 name: Install apt packages
 description: >
-  Installs apt packages with a per-attempt timeout and retries. The hosted runner's Azure apt mirror intermittently serves archives at a crawl, which apt's own timeout does not catch. A stuck attempt is killed and retried, which usually lands on a healthy mirror node.
+  Installs apt packages using Ubuntu mirrors and bounded download retries. Caches downloaded packages as an optimization; apt resolves dependencies on every run.
 
 inputs:
   packages:
-    description: Space separated list of packages to install
+    description: Space separated list of package names to install
     required: true
   attempts:
-    description: Maximum number of attempts
+    description: Maximum number of download attempts
     default: "3"
   attempt-timeout:
-    description: Seconds before a single attempt is killed
+    description: Seconds before a single download attempt is killed
     default: "180"
 runs:
   using: composite
   steps:
+    - name: Identify apt cache
+      id: cache-key
+      shell: bash
+      env:
+        PACKAGES: ${{ inputs.packages }}
+      run: |
+        . /etc/os-release
+        packages_hash=$(printf '%s' "$PACKAGES" | sha256sum | cut -d ' ' -f 1)
+        # Cached downloads are optional: apt fetches any missing/newer packages.
+        # Refresh weekly, including inside job containers without ImageVersion.
+        echo "key=apt-v2-${ID}-${VERSION_ID}-$(dpkg --print-architecture)-$(date -u +%G-%V)-${packages_hash}" >> "$GITHUB_OUTPUT"
+    - name: Restore apt packages
+      id: cache
+      uses: actions/cache/restore@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+      with:
+        path: |
+          ${{ runner.temp }}/apt-packages/*.deb
+          ${{ runner.temp }}/apt-packages/.keep
+        key: ${{ steps.cache-key.outputs.key }}
     - name: Install ${{ inputs.packages }}
       shell: bash
       env:
         PACKAGES: ${{ inputs.packages }}
         ATTEMPTS: ${{ inputs.attempts }}
         ATTEMPT_TIMEOUT: ${{ inputs.attempt-timeout }}
-      run: |
-        SUDO=""
-        if [ "$(id -u)" -ne 0 ]; then
-          SUDO="sudo"
-        fi
-
-        attempt_install() {
-          $SUDO apt-get update -q
-          # Intentionally unquoted, this is a list of package names
-          $SUDO apt-get install -q --yes --no-install-recommends $PACKAGES
-        }
-        export -f attempt_install
-        export SUDO PACKAGES
-
-        for attempt in $(seq 1 "${ATTEMPTS}"); do
-          echo "::group::apt install attempt ${attempt}/${ATTEMPTS}"
-          start=$(date +%s)
-          if timeout --kill-after=10 "${ATTEMPT_TIMEOUT}" bash -c attempt_install; then
-            echo "::endgroup::"
-            echo "Installed in $(( $(date +%s) - start ))s"
-            exit 0
-          fi
-          echo "::endgroup::"
-          echo "::warning::apt install attempt ${attempt}/${ATTEMPTS} failed or exceeded ${ATTEMPT_TIMEOUT}s"
-          # A killed attempt can leave dpkg half configured
-          $SUDO dpkg --configure -a || true
-        done
-
-        echo "::error::apt install failed after ${ATTEMPTS} attempts"
-        exit 1
+        CACHE_DIR: ${{ runner.temp }}/apt-packages
+      run: bash "$GITHUB_ACTION_PATH/install.sh"
+    # Save immediately: a later test failure must not discard downloaded packages.
+    - name: Save apt packages
+      if: steps.cache.outputs.cache-hit != 'true'
+      uses: actions/cache/save@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
+      with:
+        path: |
+          ${{ runner.temp }}/apt-packages/*.deb
+          ${{ runner.temp }}/apt-packages/.keep
+        key: ${{ steps.cache-key.outputs.key }}

.github/actions/apt-install/install.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Run as root in the timed child process. Only downloads may be interrupted.
+if [ "${1:-}" = download ]; then
+	download_archive_dir=$2
+	shift 2
+	apt-get update -q
+	apt-get install -q --yes --no-install-recommends --download-only \
+		-o "Dir::Cache::archives=$download_archive_dir" "$@"
+	exit 0
+fi
+
+SUDO=()
+if [ "$(id -u)" -ne 0 ]; then
+	SUDO=(sudo)
+fi
+read -r -a requested_packages <<< "$PACKAGES"
+mkdir -p "$CACHE_DIR"
+touch "$CACHE_DIR/.keep"
+
+# Hosted runners use a mirror list; job containers can point directly at Azure.
+# Handle both layouts, leaving other repositories and signature checks intact.
+if [ -f /etc/apt/apt-mirrors.txt ]; then
+	"${SUDO[@]}" sed -i '\|azure\.archive\.ubuntu\.com|d' /etc/apt/apt-mirrors.txt
+fi
+for source in /etc/apt/sources.list /etc/apt/sources.list.d/*.list /etc/apt/sources.list.d/*.sources; do
+	if [ -f "$source" ]; then
+		"${SUDO[@]}" sed -i 's|azure\.archive\.ubuntu\.com|archive.ubuntu.com|g' "$source"
+	fi
+done
+
+for attempt in $(seq 1 "$ATTEMPTS"); do
+	echo "::group::apt download attempt ${attempt}/${ATTEMPTS}"
+	if timeout --kill-after=10 "$ATTEMPT_TIMEOUT" "${SUDO[@]}" bash "$0" download "$CACHE_DIR" "${requested_packages[@]}"; then
+		echo "::endgroup::"
+		# Apt handles aliases (e.g. libmagic1 -> libmagic1t64) and dependencies.
+		"${SUDO[@]}" apt-get install -q --yes --no-install-recommends --no-download \
+			-o "Dir::Cache::archives=$CACHE_DIR" "${requested_packages[@]}"
+		# Allow the unprivileged cache action to read archives downloaded as root.
+		find "$CACHE_DIR" -maxdepth 1 -name '*.deb' -exec "${SUDO[@]}" chmod a+r {} +
+		exit 0
+	fi
+	echo "::endgroup::"
+	echo "::warning::apt download attempt ${attempt}/${ATTEMPTS} failed or exceeded ${ATTEMPT_TIMEOUT}s"
+done
+
+echo "::error::apt download failed after ${ATTEMPTS} attempts"
+exit 1

.github/workflows/ci-backend.yml

@@ -76,6 +76,7 @@ jobs:
               - 'uv.lock'
               - 'docker/compose/docker-compose.ci-test.yml'
               - '.github/workflows/ci-backend.yml'
+              - '.github/actions/apt-install/**'
   test:
     needs: changes
     if: needs.changes.outputs.backend_changed == 'true'

.github/workflows/ci-frontend.yml

@@ -68,6 +68,7 @@ jobs:
             frontend:
               - 'src-ui/**'
               - '.github/workflows/ci-frontend.yml'
+              - '.github/actions/apt-install/**'
   install-dependencies:
     needs: changes
     if: needs.changes.outputs.frontend_changed == 'true'