build: pin brightnessctl in a persistent local Gentoo overlay

hydra/build.py

@@ -237,8 +237,7 @@ if path.exists():
         if step == 'fetch':
             inputs = json.loads((self.source_dir / 'image/sources.json').read_text())
             try:
-                for name in ('stage3', 'portage'):
-                    item = inputs[name]
+                for item in [inputs['stage3'], inputs['portage'], *inputs.get('local_packages', [])]:
                     path = self.cache / item.get('filename', Path(urllib.parse.urlparse(item['url']).path).name)
                     verify_hash(path, item['sha256'])
             except (OSError, BuildError):
@@ -276,6 +275,8 @@ if path.exists():
         verify_hash(archive, stage['sha256'])
         snapshot = self.download(inputs['portage']['url'], inputs['portage']['filename'])
         verify_hash(snapshot, inputs['portage']['sha256'])
+        for item in inputs.get('local_packages', []):
+            verify_hash(self.download(item['url'], item['filename']), item['sha256'])
         signature = self.download(stage['signature_url'])
         keyring = self.download(inputs['keyring_url'])
         verify_hash(keyring, inputs['keyring_sha256'])
@@ -316,6 +317,9 @@ if [ ! -f /var/db/repos/gentoo/.hydra-snapshot ]; then
   printf '%s\\n' '{inputs['portage']['commit']}' > /var/db/repos/gentoo/.hydra-snapshot
 fi
 cp -a /hydra-source/image/portage/. /etc/portage/
+mkdir -p /var/db/repos/hydra /var/cache/distfiles
+cp -a /hydra-source/image/overlay/. /var/db/repos/hydra/
+cp /hydra-cache/brightnessctl-0.5.1.tar.gz /var/cache/distfiles/brightnessctl-0.5.1.tar.gz
 mkdir -p /etc/portage/patches/app-emulation/qemu /etc/portage/patches/app-emulation/virt-viewer
 cp /hydra-source/patches/qemu-virtio-refresh-rate.patch /etc/portage/patches/app-emulation/qemu/10-hydra-refresh.patch
 cp /hydra-source/patches/virt-viewer-hydra-session.patch /etc/portage/patches/app-emulation/virt-viewer/10-hydra-session.patch