Split host setup into explicit entity actions

actions/config/base.py

@@ -0,0 +1,40 @@
+"""Apply the common APT archive and journald retention policy."""
+from pathlib import Path
+from engine.descriptor import Meta
+
+METADATA = Meta(summary="Configure APT archive cleanup and journald retention.")
+
+
+def _configure(ctx, path, legacy, content, restart=False):
+    for target in (path, legacy):
+        if target.is_symlink():
+            raise RuntimeError(f"Refusing redirected configuration: {target}")
+    previous = path.read_text() if path.exists() else None
+    backup = ctx.host.backup(str(legacy), sudo=True) if legacy.exists() else None
+    if previous == content and not backup:
+        return
+    if previous != content:
+        ctx.host.write_file(str(path), content, sudo=True)
+    if backup:
+        ctx.sys.sudo(["rm", "--", str(legacy)])
+    if restart:
+        try:
+            ctx.sys.sudo(["systemctl", "restart", "systemd-journald"])
+        except Exception:
+            if backup:
+                ctx.sys.sudo(["cp", "--preserve=all", "--", backup, str(legacy)])
+            if previous is None:
+                ctx.sys.sudo(["rm", "--", str(path)])
+            elif previous != content:
+                ctx.host.write_file(str(path), previous, backup=False, sudo=True)
+            raise
+
+
+def run(ctx, args):
+    if not Path("/etc/debian_version").is_file():
+        raise RuntimeError("Debian required.")
+    apt = Path("/etc/apt/apt.conf.d")
+    journal = Path("/etc/systemd/journald.conf.d")
+    _configure(ctx, apt / "99-apex", apt / "01clean", 'APT::Keep-Downloaded-Packages "0";\n')
+    _configure(ctx, journal / "99-apex.conf", journal / "maxuse.conf",
+               "[Journal]\nSystemMaxUse=200M\n", restart=True)