diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index d8cf893..9a18a90 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -19,6 +19,33 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # setup-php installs PHP 8.3+ through php-builder, which apt-installs ~70
+      # -dev packages before unpacking the build (#178). Ubuntu's image deletes
+      # the .debs after install, so every job re-downloads them. Keeping them
+      # and restoring them from the cache server, which lives in the cluster,
+      # turns a WAN download into a local one.
+      #
+      # Keyed per PHP version because the install path differs by version and
+      # the package sets are not interchangeable: 8.3+ pulls the ~70 -dev
+      # packages through php-builder, while 8.1 and 8.2 come from the ondrej
+      # PPA as a handful of runtime packages. Sharing one key across both lets
+      # whichever job finishes first decide what the others restore, and 8.1 is
+      # always first.
+      #
+      # Only the .debs are cached, never /var/lib/apt/lists — a stale index is
+      # how you get 404s mid-install.
+      - name: Keep downloaded .debs
+        run: |
+          sudo rm -f /etc/apt/apt.conf.d/docker-clean
+          echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' \
+            | sudo tee /etc/apt/apt.conf.d/99keep-downloaded-packages >/dev/null
+
+      - name: Cache apt packages
+        uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives/*.deb
+          key: apt-php8.3-${{ runner.arch }}-v1
+
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
@@ -26,7 +53,7 @@ jobs:
           tools: composer:v2
 
       - name: Cache Composer packages
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ~/.composer/cache
           key: composer-${{ hashFiles('composer.json') }}
@@ -50,9 +77,37 @@ jobs:
           - '8.1'
           - '8.2'
           - '8.3'
+          - '8.5'
     steps:
       - uses: actions/checkout@v4
 
+      # setup-php installs PHP 8.3+ through php-builder, which apt-installs ~70
+      # -dev packages before unpacking the build (#178). Ubuntu's image deletes
+      # the .debs after install, so every job re-downloads them. Keeping them
+      # and restoring them from the cache server, which lives in the cluster,
+      # turns a WAN download into a local one.
+      #
+      # Keyed per PHP version because the install path differs by version and
+      # the package sets are not interchangeable: 8.3+ pulls the ~70 -dev
+      # packages through php-builder, while 8.1 and 8.2 come from the ondrej
+      # PPA as a handful of runtime packages. Sharing one key across both lets
+      # whichever job finishes first decide what the others restore, and 8.1 is
+      # always first.
+      #
+      # Only the .debs are cached, never /var/lib/apt/lists — a stale index is
+      # how you get 404s mid-install.
+      - name: Keep downloaded .debs
+        run: |
+          sudo rm -f /etc/apt/apt.conf.d/docker-clean
+          echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' \
+            | sudo tee /etc/apt/apt.conf.d/99keep-downloaded-packages >/dev/null
+
+      - name: Cache apt packages
+        uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives/*.deb
+          key: apt-php${{ matrix.php }}-${{ runner.arch }}-v1
+
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
@@ -62,7 +117,7 @@ jobs:
           tools: composer:v2
 
       - name: Cache Composer packages
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ~/.composer/cache
           key: ${{ matrix.php }}-composer-${{ hashFiles('composer.json') }}
@@ -96,6 +151,33 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      # setup-php installs PHP 8.3+ through php-builder, which apt-installs ~70
+      # -dev packages before unpacking the build (#178). Ubuntu's image deletes
+      # the .debs after install, so every job re-downloads them. Keeping them
+      # and restoring them from the cache server, which lives in the cluster,
+      # turns a WAN download into a local one.
+      #
+      # Keyed per PHP version because the install path differs by version and
+      # the package sets are not interchangeable: 8.3+ pulls the ~70 -dev
+      # packages through php-builder, while 8.1 and 8.2 come from the ondrej
+      # PPA as a handful of runtime packages. Sharing one key across both lets
+      # whichever job finishes first decide what the others restore, and 8.1 is
+      # always first.
+      #
+      # Only the .debs are cached, never /var/lib/apt/lists — a stale index is
+      # how you get 404s mid-install.
+      - name: Keep downloaded .debs
+        run: |
+          sudo rm -f /etc/apt/apt.conf.d/docker-clean
+          echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' \
+            | sudo tee /etc/apt/apt.conf.d/99keep-downloaded-packages >/dev/null
+
+      - name: Cache apt packages
+        uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives/*.deb
+          key: apt-php8.3-${{ runner.arch }}-v1
+
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with: