refactor(ops): add operations/cache.py + operations/host.py seam (W2)

Extracts pure, click-free cargo-cache status/purge and host disk/runner/
backup-template logic into operations/, mirroring the W1 pattern. Routes
commands/retention.py::_purge_cargo_cache through operations.cache while
preserving identical CLI output. commands/monitor.py is left untouched
(its refactor is optional per the plan; the Windows/Linux polymorphic
_service_status and the disk not-found detection don't map cleanly onto
the new pure functions without risking behavioural drift).

tests/python/test_operations_cache.py

@@ -0,0 +1,187 @@
+"""Tests for the pure ``operations.cache`` layer (W2 of the web-UI plan).
+
+Covers ``cargo_cache_status`` and ``purge_cargo_cache`` — the seam both the
+CLI (``retention run``) and the future web UI import for cargo-cache
+state/maintenance. Zero ``click``/``print`` in the module under test.
+"""
+
+from __future__ import annotations
+
+import time
+from pathlib import Path
+
+from ci_orchestrator.cargo_cache import CargoCacheStore, cache_key
+from ci_orchestrator.config import BackendConfig, CargoCacheConfig, Config, Paths
+from ci_orchestrator.operations.cache import (
+    CacheStatus,
+    PurgeResult,
+    cargo_cache_status,
+    purge_cargo_cache,
+)
+
+
+def _make_config(root: Path, *, enabled: bool = True, retention_days: int = 30) -> Config:
+    return Config(
+        paths=Paths(
+            root=root.parent,
+            templates=root.parent / "templates",
+            build_vms=root.parent / "build-vms",
+            artifacts=root.parent / "artifacts",
+            keys=root.parent / "keys",
+        ),
+        backend=BackendConfig(),
+        cargo_cache=CargoCacheConfig(enabled=enabled, root=root, retention_days=retention_days),
+    )
+
+
+def _seed_entry(root: Path, digest: str, *, age_days: int, size: int = 1024) -> Path:
+    store = CargoCacheStore(root)
+    src = root.parent / f"seed-{digest}.tar.zst"
+    src.parent.mkdir(parents=True, exist_ok=True)
+    src.write_bytes(b"x" * size)
+    entry = store.publish(cache_key(lock_digest=digest, rustc_version="r", host_triple="t"), src)
+    stamp = time.time() - age_days * 86400
+    import os
+
+    os.utime(entry, (stamp, stamp))
+    return entry
+
+
+# ── cargo_cache_status ──────────────────────────────────────────────────────
+
+
+def test_cargo_cache_status_missing_root(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    config = _make_config(root)
+
+    status = cargo_cache_status(config)
+
+    assert status == CacheStatus(
+        root=root,
+        total_bytes=0,
+        entry_count=0,
+        oldest_age_days=None,
+        retention_days=30,
+    )
+
+
+def test_cargo_cache_status_empty_root(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    root.mkdir(parents=True)
+    config = _make_config(root)
+
+    status = cargo_cache_status(config)
+
+    assert status.entry_count == 0
+    assert status.total_bytes == 0
+    assert status.oldest_age_days is None
+
+
+def test_cargo_cache_status_populated_with_aged_entries(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    _seed_entry(root, "old", age_days=90, size=2048)
+    _seed_entry(root, "new", age_days=1, size=1024)
+    config = _make_config(root, retention_days=30)
+
+    status = cargo_cache_status(config)
+
+    assert status.entry_count == 2
+    assert status.total_bytes == 2048 + 1024
+    assert status.oldest_age_days is not None
+    assert status.oldest_age_days >= 89
+    assert status.retention_days == 30
+    assert status.root == root
+
+
+def test_cargo_cache_status_ignores_incoming_staging_dir(tmp_path: Path) -> None:
+    """The ``.incoming`` staging directory used by ``publish()`` is not a real entry."""
+    root = tmp_path / "cache" / "cargo"
+    _seed_entry(root, "one", age_days=1)
+    (root / ".incoming").mkdir(parents=True, exist_ok=True)
+
+    config = _make_config(root)
+    status = cargo_cache_status(config)
+
+    assert status.entry_count == 1
+
+
+def test_cargo_cache_status_reports_even_when_disabled(tmp_path: Path) -> None:
+    """Status is descriptive of disk state; ``enabled`` only gates purging."""
+    root = tmp_path / "cache" / "cargo"
+    _seed_entry(root, "old", age_days=90)
+    config = _make_config(root, enabled=False)
+
+    status = cargo_cache_status(config)
+
+    assert status.entry_count == 1
+
+
+# ── purge_cargo_cache ────────────────────────────────────────────────────────
+
+
+def test_purge_cargo_cache_dry_run_counts_only_no_delete(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    old = _seed_entry(root, "old", age_days=90, size=3 * 1024 * 1024)
+    config = _make_config(root, retention_days=30)
+
+    result = purge_cargo_cache(config, dry_run=True)
+
+    assert result == PurgeResult(removed_entries=1, freed_bytes=3 * 1024 * 1024, dry_run=True)
+    assert old.exists(), "dry_run must not delete anything"
+
+
+def test_purge_cargo_cache_real_purge_removes_only_old(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    old = _seed_entry(root, "old", age_days=90)
+    fresh = _seed_entry(root, "new", age_days=1)
+    config = _make_config(root, retention_days=30)
+
+    result = purge_cargo_cache(config)
+
+    assert result.removed_entries == 1
+    assert result.dry_run is False
+    assert not old.exists()
+    assert fresh.exists()
+
+
+def test_purge_cargo_cache_retention_override_wins_over_config(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    entry = _seed_entry(root, "mid", age_days=10)
+    config = _make_config(root, retention_days=30)  # config alone would spare this entry
+
+    result = purge_cargo_cache(config, retention_days=7)
+
+    assert result.removed_entries == 1
+    assert not entry.exists()
+
+
+def test_purge_cargo_cache_disabled_returns_zero_and_does_not_touch_disk(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    old = _seed_entry(root, "old", age_days=90)
+    config = _make_config(root, enabled=False, retention_days=30)
+
+    result = purge_cargo_cache(config)
+
+    assert result == PurgeResult(removed_entries=0, freed_bytes=0, dry_run=False)
+    assert old.exists()
+
+
+def test_purge_cargo_cache_nothing_to_purge(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    fresh = _seed_entry(root, "new", age_days=1)
+    config = _make_config(root, retention_days=30)
+
+    result = purge_cargo_cache(config)
+
+    assert result.removed_entries == 0
+    assert result.freed_bytes == 0
+    assert fresh.exists()
+
+
+def test_purge_cargo_cache_missing_root_is_not_an_error(tmp_path: Path) -> None:
+    root = tmp_path / "cache" / "cargo"
+    config = _make_config(root, retention_days=30)
+
+    result = purge_cargo_cache(config)
+
+    assert result == PurgeResult(removed_entries=0, freed_bytes=0, dry_run=False)