fixup! Add browsers for tests: Playwright, Firefox, geckodriver, headless Chrome (closes #10)

Model: deepseek-v4-pro

build.sh

@@ -99,10 +99,15 @@ curl -fsSL https://packages.mozilla.org/apt/repo-signing-key.gpg \
     -o /etc/apt/keyrings/packages.mozilla.org.asc
 echo "deb [signed-by=/etc/apt/keyrings/packages.mozilla.org.asc] https://packages.mozilla.org/apt mozilla main" \
     > /etc/apt/sources.list.d/mozilla.list
+cat > /etc/apt/preferences.d/mozilla <<'EOF'
+Package: *
+Pin: origin packages.mozilla.org
+Pin-Priority: 1000
+EOF
 apt-get update
 apt-get -y install --no-install-recommends -t mozilla firefox
 
-# geckodriver, matched to Firefox at its current release.
+# geckodriver, at its latest release (independent of the Firefox version).
 gd="$(latest_tag mozilla/geckodriver)"
 case "$arch" in
     arm64) gd_arch=linux-aarch64 ;;
@@ -111,12 +116,16 @@ esac
 curl -fsSL "https://github.com/mozilla/geckodriver/releases/download/${gd}/geckodriver-${gd}-${gd_arch}.tar.gz" |
     tar -C /usr/local/bin -xz geckodriver
 
-# Playwright's Chromium and Firefox. WebKit has no linux-arm64 build, so it
-# is skipped. Playwright's Chromium is also the headless Chrome for
+# Playwright's Chromium and Firefox. WebKit is skipped because no repository
+# uses it today. Playwright's Chromium is also the headless Chrome for
 # chromedp-style clients, exposed as `chromium` on PATH.
 playwright install --with-deps chromium firefox
-ln -s "$(ls -d "$PLAYWRIGHT_BROWSERS_PATH"/chromium-*/chrome-linux*/chrome | head -n1)" \
-    /usr/local/bin/chromium
+chromiums=( "$PLAYWRIGHT_BROWSERS_PATH"/chromium-*/chrome-linux*/chrome )
+if [ "${#chromiums[@]}" -ne 1 ] || [ ! -x "${chromiums[0]}" ]; then
+    echo "error: expected exactly one chromium binary, found ${#chromiums[@]}" >&2
+    exit 1
+fi
+ln -s "${chromiums[0]}" /usr/local/bin/chromium
 
 # --- pyenv, Python (latest), pip, virtualenv ---------------------------------
 git clone -q --depth 1 --branch "$PYENV_GIT_TAG" https://github.com/pyenv/pyenv.git "$PYENV_ROOT"