Add an integration test suite that boots ISO scenarios in QEMU (#109)

* Move the unit tests under test/unit

test/ is growing an integration suite; the fast, VM-free tests get their
own directory so the two kinds cannot be confused. test/all keeps its
role as the aggregate runner for everything that needs no built ISO.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Add an integration suite that boots ISO scenarios in QEMU

test/integration installs an ISO once — unattended, from a generated
cidata drive — and saves a reusable base image; each scenario in
test/integration.d/ then boots a throwaway overlay with its own copy of
the firmware vars. Shared machinery (VM lifecycle, QMP screendump + OCR
console driving, virtual keystrokes, guest SSH, the cidata build) lives
in base-test.sh, so a new scenario is one file.

The first scenario proves omarchy-system-factory-reset hands a machine
on without destroying a shared ESP: a Windows entry and a foreign Linux
with its own machine-id, boot directory, and UKIs must survive both the
staged reset and the first-boot provisioning that follows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Let omarchy-iso-make keep the host package cache

Purging /var/cache/pacman/pkg needs interactive sudo, which blocks
unattended builds. --keep-pkg-cache skips the purge so test rigs and
agents can build an ISO without a prompt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

test/unit/test_offline_mirror_pruning.py

@@ -0,0 +1,79 @@
+#!/usr/bin/python
+
+import subprocess
+import tempfile
+import unittest
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[2]
+PRUNER = ROOT / "builder/prune-offline-mirror.sh"
+
+
+class OfflineMirrorPruningTest(unittest.TestCase):
+    def run_pruner(self, mirror: Path, required: list[str]):
+        return subprocess.run(
+            ["bash", str(PRUNER), str(mirror)],
+            input="".join(f"{filename}\n" for filename in required),
+            capture_output=True,
+            text=True,
+        )
+
+    def add_file(self, mirror: Path, filename: str):
+        (mirror / filename).write_bytes(b"package")
+
+    def test_keeps_only_exactly_selected_package_archives(self):
+        with tempfile.TemporaryDirectory() as directory:
+            mirror = Path(directory)
+            keep = "keep-2.0-1-x86_64.pkg.tar.zst"
+            other = "other-1.0-1-any.pkg.tar.zst"
+            stale_version = "keep-1.0-1-x86_64.pkg.tar.zst"
+            removed_package = "removed-1.0-1-x86_64.pkg.tar.zst"
+            orphan_signature = "interrupted-1.0-1-x86_64.pkg.tar.zst.sig"
+
+            for filename in (keep, other, stale_version, removed_package):
+                self.add_file(mirror, filename)
+            for filename in (keep, stale_version, removed_package):
+                self.add_file(mirror, f"{filename}.sig")
+            self.add_file(mirror, orphan_signature)
+            self.add_file(mirror, "offline.db.tar.gz")
+
+            result = self.run_pruner(mirror, [keep, other])
+
+            self.assertEqual(result.returncode, 0, result.stderr)
+            self.assertEqual(
+                {path.name for path in mirror.iterdir()},
+                {keep, f"{keep}.sig", other, "offline.db.tar.gz"},
+            )
+            self.assertIn(stale_version, result.stdout)
+            self.assertIn(removed_package, result.stdout)
+
+    def test_missing_selection_aborts_before_deleting_anything(self):
+        with tempfile.TemporaryDirectory() as directory:
+            mirror = Path(directory)
+            cached = "cached-1.0-1-x86_64.pkg.tar.zst"
+            self.add_file(mirror, cached)
+
+            result = self.run_pruner(
+                mirror, ["missing-1.0-1-x86_64.pkg.tar.zst"]
+            )
+
+            self.assertNotEqual(result.returncode, 0)
+            self.assertTrue((mirror / cached).exists())
+            self.assertIn("selected packages are missing", result.stderr)
+
+    def test_empty_selection_aborts_before_deleting_anything(self):
+        with tempfile.TemporaryDirectory() as directory:
+            mirror = Path(directory)
+            cached = "cached-1.0-1-x86_64.pkg.tar.zst"
+            self.add_file(mirror, cached)
+
+            result = self.run_pruner(mirror, [])
+
+            self.assertNotEqual(result.returncode, 0)
+            self.assertTrue((mirror / cached).exists())
+            self.assertIn("empty package selection", result.stderr)
+
+
+if __name__ == "__main__":
+    unittest.main()