Add threat model + security-model discoverability (AGENTS.md -> SECURITY.md -> THREAT_MODEL.md) (#17823)

Author: potiuk

CLAUDE.md

@@ -185,4 +185,11 @@ The project uses compile-time i18n via the `build-helper-maven-plugin`. The prop
 
 ## Git Commit
 
-- Do NOT add `Co-Authored-By` trailer to commit messages.
+- Do NOT add `Co-Authored-By` trailer to commit messages.
+
+## Security
+
+Security model: [SECURITY.md](./SECURITY.md)
+
+Agents that scan this repository should consult `SECURITY.md` and the
+threat model it links before reporting issues.

SECURITY.md

@@ -0,0 +1,29 @@
+<!--
+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.
+-->
+
+# Security Policy
+
+## Reporting a Vulnerability
+
+`apache/iotdb` follows the [Apache Software Foundation security process](https://www.apache.org/security/). Please report suspected
+vulnerabilities privately to `security@apache.org`; do not open public
+GitHub issues or pull requests for security reports.
+
+## Threat Model
+
+What the project treats as in scope and out of scope, the security
+properties it provides and disclaims, the adversary model, and how
+findings are triaged are documented in [THREAT_MODEL.md](./THREAT_MODEL.md).