Add umbrella threat model + AGENTS.md and link from SECURITY.md for security-model discoverability

AGENTS.md

@@ -0,0 +1,34 @@
+<!--
+SPDX-License-Identifier: Apache-2.0
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+# Agent Guide for Apache CXF
+
+This file is read by automated agents (security scanners, code analyzers,
+AI assistants) operating on this repository. It points them at the
+human-authored references they should consult before producing output.
+
+## Security
+
+Security model: [SECURITY.md](./SECURITY.md) -> [THREAT_MODEL.md](./THREAT_MODEL.md)
+
+Agents that scan this repository should consult `SECURITY.md` and the linked
+`THREAT_MODEL.md` for the project's threat model before reporting issues. Note
+that CXF is a *framework*: it provides security mechanisms (WS-Security, TLS
+conduits, authorization interceptors, XML-processing limits) and many
+properties are conditional on how the integrator configures them. The model
+covers the runtime SOAP/JAX-WS and REST/JAX-RS pipeline, WS-Security
+processing, XML parsing (XXE/DoS), the SSRF surface of remote
+WSDL/schema/MTOM resolution, and JAX-RS provider deserialization.

SECURITY.md

@@ -13,3 +13,13 @@
 
 For information on how to report a new security problem please see [here](https://www.apache.org/security/).
 Our existing security advisories are published [here](https://cxf.apache.org/security-advisories.html).
+
+## Threat Model
+
+What CXF treats as in scope and out of scope, the security properties it
+provides and the ones it disclaims, the adversary model, and how inbound
+reports and tool/AI findings are triaged are documented in
+[THREAT_MODEL.md](./THREAT_MODEL.md). Because CXF is a framework, many of those
+properties are conditional on how the integrator configures it; the
+integrator-responsibilities and known-non-findings sections of that document
+are the most useful starting points for triaging a report.