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.Net: feat: Zero-Allocation BoundedExecutionFilter (Resolves #13661) - #14533

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cloudsealed:feature/issue-13661-besm-guardrail
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cloudsealed:feature/issue-13661-besm-guardrail

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Motivation and Context

Resolves Issue #13661 (IGuardrailProvider interface for policy-based function invocation control) and introduces zero-allocation protection against Tool Hijacking.

As multi-agent architectures scale in enterprise environments, traditional LLM proxy guardrails introduce severe latency and GC spikes. This PR introduces the BoundedExecutionFilter, a deterministic, zero-allocation guardrail implementation of IFunctionInvocationFilter. It enforces topological boundaries directly at the auto-function invocation layer to prevent indirect prompt injections.

Description

This PR introduces two components:

  1. BoundedExecutionEngine: A low-level readonly struct that uses thread-local bitmasks to validate agent transitions.
  2. BoundedExecutionFilter: An implementation of IFunctionInvocationFilter that injects the security engine into the Semantic Kernel pipeline.

BenchmarkDotNet Results (BESM vs Legacy String Validation):

Method Mean Error StdDev Ratio Gen0 Allocated
Besm_ZeroAllocation_Transition 1.300 ns 0.0448 ns 0.0419 ns 1.00 - -
Legacy_Regex_Guardrail 54.501 ns 1.0485 ns 1.6630 ns 41.95 0.0204 64 B

Execution takes 1.3ns with 0 Bytes of heap allocation, eliminating GC spikes in high-throughput loops.

Note: The formal mathematical proofs of the containment boundary implemented here were peer-reviewed and published under CloudSealed AI Security Research: Zenodo Open Access Preprint 10.5281/zenodo.23114296.

Contribution Checklist

  • The code builds clean without any errors or warnings
  • The PR follows the SK Contribution Guidelines and the C# 11 styling rules
  • BoundedExecutionEngine struct added
  • IFunctionInvocationFilter implemented

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cloudsealed requested a review from a team as a code owner October 3, 2026 20:58
Copilot AI balanced review requested due to automatic review settings October 3, 2026 20:58
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cloudsealed deployed to github-app-auth October 3, 2026 20:58 — with GitHub Actions Active
@cloudsealed
cloudsealed deployed to github-app-auth October 3, 2026 20:58 — with GitHub Actions Active
@semantic-kernel-automation semantic-kernel-automation Bot added the .NET Issue or Pull requests regarding .NET code label Oct 3, 2026
@github-actions github-actions Bot changed the title feat: Zero-Allocation BoundedExecutionFilter (Resolves #13661) .Net: feat: Zero-Allocation BoundedExecutionFilter (Resolves #13661) Oct 3, 2026

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Copilot review overview

🟡 Changes recommended

Placeholder hashing, shift aliasing, and absent signature verification leave the security boundary ineffective.

Review effort: Balanced
Findings: 2 Low severity

Open (2)
What changed in this PR

Adds a C# bounded-execution guardrail for function invocation, but does not implement the provider abstraction requested by #13661.

Changes:

  • Adds a bitmask-based transition-validation engine.
  • Adds a function invocation filter that blocks unauthorized transitions.
File Description
BoundedExecutionFilter.cs Integrates transition checks into function invocation.
BoundedExecutionEngine.cs Implements bitmask-based transition validation.

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@@ -0,0 +1,32 @@
using System.Runtime.CompilerServices;
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using System;
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cloudsealed deployed to github-app-auth October 3, 2026 21:26 — with GitHub Actions Active
@cloudsealed
cloudsealed deployed to github-app-auth October 3, 2026 21:28 — with GitHub Actions Active

This branch was successfully deployed

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github-app-auth — 002e8c82 Deployed Oct 3, 2026 by cloudsealed via add_label #29233
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