fix(ip-pool): reconcile stale leases against live clones (§2.8, W1)

A job killed mid-flight never released its IP lease; with only 4 pool addresses a single leak exhausted the pool ("IP pool exhausted after 60s"). IpSlotPool.reconcile() releases leases whose owner clone-dir is gone; vm cleanup runs it only against the real build_vms base. Closes TODO §2.8.

tests/python/test_ip_pool.py

@@ -115,3 +115,45 @@ def test_non_dict_lease_json_treated_as_empty(tmp_path: Path) -> None:
     pool = make_pool(tmp_path)
     ip = pool.acquire("owner-1")
     assert ip == "10.0.0.1"
+
+
+# ── reconcile (TODO §2.8) ─────────────────────────────────────────────────────
+
+
+def test_reconcile_releases_leases_with_dead_owners(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    pool.acquire("clone-alive")   # 10.0.0.1
+    pool.acquire("clone-dead")    # 10.0.0.2
+
+    released = pool.reconcile({"clone-alive"})
+
+    assert released == ["10.0.0.2"]
+    leases = json.loads((tmp_path / "ip-pool.json").read_text())
+    assert leases["10.0.0.1"] == "clone-alive"  # kept
+    assert leases["10.0.0.2"] is None           # released
+
+
+def test_reconcile_keeps_all_when_all_owners_live(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    pool.acquire("clone-a")
+    pool.acquire("clone-b")
+    assert pool.reconcile({"clone-a", "clone-b"}) == []
+    leases = json.loads((tmp_path / "ip-pool.json").read_text())
+    assert leases["10.0.0.1"] == "clone-a"
+    assert leases["10.0.0.2"] == "clone-b"
+
+
+def test_reconcile_dry_run_reports_without_writing(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)
+    pool.acquire("clone-dead")  # 10.0.0.1
+
+    released = pool.reconcile(set(), dry_run=True)
+
+    assert released == ["10.0.0.1"]
+    leases = json.loads((tmp_path / "ip-pool.json").read_text())
+    assert leases["10.0.0.1"] == "clone-dead"  # untouched
+
+
+def test_reconcile_empty_pool_returns_empty(tmp_path: Path) -> None:
+    pool = make_pool(tmp_path)  # no acquires → all leases None
+    assert pool.reconcile(set()) == []