Add security threat model (THREAT_MODEL.md) + SECURITY.md and AGENTS.md discoverability

AGENTS.md

@@ -28,3 +28,33 @@ Applies to the whole repository unless a deeper `AGENTS.md` overrides it.
 
 ## UI
 - UI-specific rules live in `ui/AGENTS.md` and deeper UI-level files.
+
+## Security
+
+You are helping a security researcher find and report vulnerabilities in
+Apache StreamPipes. Before drafting any report or reaching any conclusion,
+complete these steps.
+
+### Step 1 — Read the threat model
+Read **[THREAT_MODEL.md](THREAT_MODEL.md)**: the trust boundaries (the REST
+front door, the external-data ingestion boundary at the adapters, the
+extension runtime), the adversaries in and out of scope, and what StreamPipes
+upholds versus what it leaves to the operator.
+
+### Step 2 — Read the security policy
+Read **[SECURITY.md](SECURITY.md)** for how to report (`security@streampipes.apache.org`).
+
+### Key scoping facts (see THREAT_MODEL.md)
+- The **streampipes-rest** HTTP/REST layer is the primary control boundary; the external-data  ingestion boundary is at the adapters. The broker, datastore, and extension-runtime services are assumed to run inside an operator-controlled perimeter. 
+- **Installed extensions (custom adapters / processors / sinks) are
+  code-execution by design**, not a sandbox.
+- An **adapter ingesting data from an external source** is the intended
+  function; source trust and the handling guarantee for hostile ingested data
+  are spelled out in THREAT_MODEL.md.
+- Transport security (TLS), network isolation, and extension vetting are
+  **operator** responsibilities, not engine invariants.
+
+### Step 3 — Route the finding
+Route the finding to exactly one disposition in **THREAT_MODEL.md §10**
+(VALID, or one of the `OUT-OF-MODEL` / `BY-DESIGN` dispositions) and cite the
+section that justifies the call. This model is **v0**.

SECURITY.md

@@ -0,0 +1,40 @@
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to you 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
+
+    http://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
+
+Please report suspected security vulnerabilities in Apache StreamPipes
+**privately** to the StreamPipes security list at
+`security@streampipes.apache.org`, following the [Apache Software Foundation security process](https://www.apache.org/security/).
+Do **not** open public GitHub issues or pull requests for security reports — a
+private report lets the issue be investigated and fixed before disclosure.
+
+## Threat Model
+A threat model for Apache StreamPipes is maintained in
+[THREAT_MODEL.md](THREAT_MODEL.md). It describes the trust boundaries (the REST
+front door, the external-data ingestion boundary at the adapters, the
+extension runtime), the adversaries in and out of scope, the security
+properties StreamPipes upholds given its deployment assumptions versus those
+left to the operator (transport security, network isolation, extension
+vetting, source trust), and the recurring non-findings. Triagers of scanner,
+fuzzer, or AI-generated findings should route each through `THREAT_MODEL.md`
+§10.
+
+This threat model is **v0**. See `THREAT_MODEL.md` for its current status and
+maintenance notes.