Sentinel V5: Security Boundaries in Agentic Systems
Checkpoint v5 — Sentinel security boundary checkpoint: A–K complete Sentinel commit: 5e27e265eeb (master, after MR-K !83). This document and all measurement inputs live outside the repository. It records what was measured and, with equal weight, what was not . Nothing here is a statement that Sentinel is secure, or that any other product is insecure. "36/36" below means 36 fixtures the team wrote…
"Sentence 1: Sentinel v5 represents a security boundary checkpoint for agentic systems. It consists of four layers, each undergoing separate changes, measurements, and approvals.
"Sentence 2: The series encompasses detection, channel, provenance, and language-aware region checkpoints. These checkpoints assess whether a text span resembles an agent-directed instruction, identifies the channel for file scanning, determines the operating context source, and identifies which parts of a .py file are considered data.
"Sentence 3: The measurement process involves using fixtures, making changes, measuring outcomes, and approving changes before proceeding to the next MR. Each change undergoes dry-running outside the repository against the same corpus.
"Sentence 4: The measurements report on agent payloads detected, clean controls flagged, and egress of payloads to a stub LLM. No network calls, commits, payload persistence, or memory-carry rows were observed.
"Sentence 5: The measurements indicate 100 out of 118 agent-directed payloads were labeled, with 18 Python docstring controls specifically designed to challenge the system. None of the controls were changed in the process.
"Sentence 6: The system maintains deterministic output with no model present in the InjectionGate path. The lexer used for Python files was verified to agree with the virtual lexer on 90 out of 90 .py files.
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