feat: APIC-style write validation, query-target=children, contract shadow mirroring (v0.21.0)

Three fidelity gaps surfaced by one broken TN2 var file (missing firewall
block), all fixed:
- writes: reject malformed fvSubnet/l3extSubnet/vnsRedirectDest ip values
  with an APIC-style 400 before any store mutation (deletes exempt)
- query engine: support query-target=children (direct children, flat
  imdata, root excluded) — was silently returning empty
- deploy mirror: materialize vzFilter/vzEntry, vzBrCP/vzSubj (+ filter and
  service-graph subject bindings) and vnsAbsGraph shadows per target site;
  undeploy removes them

E2E-verified through the real pipeline (aci-py hidden push): a TN2 var
missing the fw block now fails with 'Invalid value "." for property ip of
vnsRedirectDest ... -> 400' and nothing lands; a complete var set builds
both MS tenants with contract shadows + sgt-FW graph binding on both sites.
Suite: 914 passed.

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

tests/test_write_validation_and_children.py

@@ -0,0 +1,97 @@
+"""Malformed-property write validation (APIC-style 400) + query-target=children.
+
+Both surfaced 2026-07-07 by a TN2 push whose var file was missing the
+firewall block: the unguarded J2 template rendered ``fvSubnet ip=".1/24"``
+and ``vnsRedirectDest ip="."`` and the sim ACCEPTED both (a real APIC 400s),
+and the verification that should have caught it used ``query-target=children``
+— which the sim silently treated as unsupported and answered with empty
+imdata (a false negative)."""
+
+from __future__ import annotations
+
+import copy
+
+import pytest
+from fastapi.testclient import TestClient
+
+from aci_sim.build.orchestrator import build_site
+from aci_sim.rest_aci.app import ApicSiteState, make_apic_app
+from aci_sim.topology.loader import load_topology
+
+TOPO_PATH = "topology.yaml"
+TENANT = "VALTEST-T1"
+BD_DN = f"uni/tn-{TENANT}/BD-bd-Val1"
+
+
+@pytest.fixture(scope="module")
+def client():
+    topo = load_topology(TOPO_PATH)
+    site = topo.sites[0]
+    store = build_site(topo, site)
+    state = ApicSiteState(
+        name=site.name, site=site, topo=topo,
+        store=store, baseline=copy.deepcopy(store),
+    )
+    c = TestClient(make_apic_app(state))
+    resp = c.post(
+        "/api/aaaLogin.json",
+        json={"aaaUser": {"attributes": {"name": "admin", "pwd": "cisco"}}},
+    )
+    assert resp.status_code == 200
+    _post(c, f"uni/tn-{TENANT}", {"fvTenant": {"attributes": {"name": TENANT}}})
+    _post(c, BD_DN, {"fvBD": {"attributes": {"name": "bd-Val1", "dn": BD_DN}}})
+    return c
+
+
+def _post(client, dn: str, body: dict):
+    return client.post(f"/api/mo/{dn}.json", json=body)
+
+
+def test_malformed_fvsubnet_ip_rejected_like_real_apic(client):
+    dn = f"{BD_DN}/subnet-[.1/24]"
+    r = _post(client, dn, {"fvSubnet": {"attributes": {"ip": ".1/24", "dn": dn}}})
+    assert r.status_code == 400
+    err = r.json()["imdata"][0]["error"]["attributes"]
+    assert ".1/24" in err["text"]
+    q = client.get("/api/class/fvSubnet.json").json()
+    assert not any(
+        ".1/24" in i["fvSubnet"]["attributes"]["dn"] for i in q["imdata"]
+    ), "malformed subnet must not land in the MIT"
+
+
+def test_malformed_vnsredirectdest_rejected(client):
+    pol_dn = f"uni/tn-{TENANT}/svcCont/svcRedirectPol-pbr-Val"
+    r = _post(client, pol_dn, {"vnsSvcRedirectPol": {"attributes": {"name": "pbr-Val", "dn": pol_dn}}})
+    assert r.status_code == 200
+    dest_dn = f"{pol_dn}/RedirectDest_ip-[.]"
+    r = _post(client, dest_dn, {"vnsRedirectDest": {"attributes": {"ip": ".", "dn": dest_dn}}})
+    assert r.status_code == 400
+
+
+def test_valid_subnet_accepted_and_delete_skips_validation(client):
+    sub_dn = f"{BD_DN}/subnet-[10.99.1.1/24]"
+    r = _post(client, sub_dn, {"fvSubnet": {"attributes": {"ip": "10.99.1.1/24", "dn": sub_dn}}})
+    assert r.status_code == 200
+    # A delete carries no ip attribute — validation must not block cleanup.
+    r = _post(client, sub_dn, {"fvSubnet": {"attributes": {"dn": sub_dn, "status": "deleted"}}})
+    assert r.status_code == 200
+
+
+def test_query_target_children_returns_direct_children_flat(client):
+    # Re-create the subnet so the BD has a child to find.
+    sub_dn = f"{BD_DN}/subnet-[10.99.1.1/24]"
+    _post(client, sub_dn, {"fvSubnet": {"attributes": {"ip": "10.99.1.1/24", "dn": sub_dn}}})
+    r = client.get(f"/api/node/mo/uni/tn-{TENANT}.json?query-target=children")
+    data = r.json()
+    classes = [next(iter(i)) for i in data["imdata"]]
+    assert "fvBD" in classes, f"direct child missing: {classes}"
+    assert "fvTenant" not in classes, "root must be excluded"
+    r2 = client.get(
+        f"/api/node/mo/uni/tn-{TENANT}.json?query-target=children&target-subtree-class=fvBD"
+    )
+    classes2 = [next(iter(i)) for i in r2.json()["imdata"]]
+    assert classes2 and set(classes2) == {"fvBD"}
+    # Grandchildren (the subnet) must NOT appear — children is one level only.
+    r3 = client.get(f"/api/node/mo/{BD_DN}.json?query-target=children")
+    classes3 = [next(iter(i)) for i in r3.json()["imdata"]]
+    assert "fvSubnet" in classes3