Add local open-source ATR detection guardrail sample (HookProvider)

[eeee2345]

This adds a guardrail sample under python/03-integrate/guardrails/, alongside the existing alice-wonderfence, llama-firewall, and nvidia-nemo samples.

What it adds: an ATRGuardrailHook that runs Agent Threat Rules (ATR, https://github.com/Agent-Threat-Rule/agent-threat-rules, MIT) against incoming turns and tool arguments. ATR is an open detection ruleset for AI-agent threats; the pyatr engine matches with pattern rules in-process, so the check needs no API key, no network call, and sends no agent data off the host.

Enforcement points (stable hooks API):

• BeforeInvocationEvent -> event.cancel when a rule at or above min_severity matches the user turn.
• BeforeToolCallEvent -> event.cancel_tool when a rule matches the tool arguments.

How it complements the existing samples: WonderFence calls a hosted service; LlamaFirewall and NeMo use model-based scanners. ATR is local and deterministic, which fits data-residency-sensitive deployments and can run as a fast offline first layer.

Status -- opening as a draft on purpose: the detection core and the hook decision logic are tested locally against the real pyatr engine (injection input and injected tool arguments are blocked; benign input and benign tool args are allowed; no false positives on the benign cases). I have not yet run main.py end-to-end against Amazon Bedrock from my own environment, so I am marking this a draft until that live run is confirmed. Happy to do it, or for a maintainer with Bedrock access to verify. Flagging honestly rather than claiming an e2e I have not run.

Files: guardrail.py, main.py, README.md (use-cases template), requirements.txt. Self-contained, no infrastructure to clean up.

Happy to adjust naming, placement, or the enforcement-point choice.

[eeee2345]

Checking in after a couple of weeks of quiet — no rush, just want to make sure this landed in the right place and isn't blocked on anything I can fix. It's a local, offline HookProvider (no external calls), tested against a live Bedrock e2e run per the PR description.

If AWS prefers a different shape for security-sample contributions, or this isn't the right repo for it, happy to redirect. Otherwise just flagging it's ready whenever someone has bandwidth to take a look.

[eeee2345]

Flagging this one — realising my earlier note did not tag anyone, and I do not want to guess at an individual on an AWS-owned repo. Whoever handles security-sample contributions: it adds a local open-source ATR detection guardrail sample, mergeable against main. If AWS prefers a different shape for security samples, or this is not the right repo, happy to redirect. A clear no is more useful to me than an open PR.