perplexity: stop shipping upstream's /lib, fail closed on strays

26.9.1 added /lib/systemd/system/perplexity-local-runtime-setup.service
to the deb, and wholesale extraction made the package own /lib -- a
symlink owned by filesystem -- so pacman refused every install and
upgrade. The unit could never work here anyway: its setup script
apt-installs Docker and the NVIDIA Container Toolkit and exits on any
distro but Ubuntu, so the Arch equivalents ride optdepends instead.

package() now allowlists what leaves the deb: opt/, usr/, and that one
known unit path (deleted). Anything else stops the build rather than
shipping the next filesystem conflict.

Verified in a clean container: the published -1 reproduces the /lib
conflict; -2 installs fresh and upgrades from 26.8.4 cleanly.

pkgbuilds/perplexity/PKGBUILD

@@ -6,7 +6,7 @@
 
 pkgname=perplexity
 pkgver=26.9.1+build61614
-pkgrel=1
+pkgrel=2
 pkgdesc="Official Perplexity desktop app"
 arch=('x86_64' 'aarch64')
 url="https://www.perplexity.ai"
@@ -56,6 +56,8 @@ depends=(
 optdepends=(
   'apparmor: confine the app with the bundled user-namespace profile'
   'libappindicator-gtk3: tray icon support'
+  'docker: containerized local GPU runtime for on-device models'
+  'nvidia-container-toolkit: containerized local GPU runtime for on-device models'
 )
 
 makedepends=('libarchive')
@@ -91,6 +93,23 @@ package() {
   bsdtar -xOf "${deb}" data.tar.xz |
     bsdtar --no-same-owner -xf - -C "${pkgdir}"
 
+  # 26.9.1 started shipping a systemd unit under /lib, and owning /lib -- a
+  # symlink owned by the filesystem package -- makes pacman refuse the whole
+  # transaction. The unit is also a no-op here:
+  # its setup script apt-installs Docker and the NVIDIA Container Toolkit and
+  # exits on any distro but Ubuntu (install those yourself; see optdepends).
+  # Delete it, but only it: anything else arriving outside the trees this
+  # PKGBUILD expects stops the build rather than shipping the next conflict.
+  local unexpected
+  unexpected=$(cd "${pkgdir}" && find . \( -type f -o -type l \) | grep -vE \
+    '^\./(opt|usr)/|^\./lib/systemd/system/perplexity-local-runtime-setup\.service$' || true)
+  if [[ -n "${unexpected}" ]]; then
+    echo "Unexpected files outside opt/ and usr/ in the upstream deb:" >&2
+    echo "${unexpected}" >&2
+    return 1
+  fi
+  rm -rf "${pkgdir}/lib"
+
   # pacman never runs the deb's postinst, so the /usr/bin entry it would have
   # symlinked is a launcher here instead, and the menu entry goes through it so
   # the flags file applies there too. The scheme handler stays upstream's.