This is the primary/submitted model. Fine-tuned microsoft/deberta-v3-small (142M params) binary classifier that detects indirect prompt injection (IPI) hidden in tool outputs (files, webpages, API responses) read by an LLM agent mid-task.

Trained from the vanilla pretrained checkpoint (never fine-tuned from or distilled against PromptGuard/ProtectAI) on a curated pool of public IPI datasets (NotInject, MAlmasabi, BIPIA, prodnull) plus a small amount of self-authored content — 10,433 examples, 3 epochs, local MPS (fp32).

For the harvest-retrain experiment built on top of this checkpoint, see knakul242/agent-context-guardrail-primary-retrain-experimental — not a replacement for this model, reported separately as a red-team before/after comparison.

Fully robust (0% bypass, static pass): direct_override, fake_system_tag, role_reframe, encoding_obfuscation, unicode_obfuscation, payload_split, fictional_framing. Weak spots: needle_in_haystack (100% bypass out-of-window — a 512-token truncation artifact, not a semantic miss; 0% in-window), low_resource_language (62.5% bypass, 5/8 seeds).

Under adversarial escalation (LLM-mutated seeds, not a single static probe), 5 of the 7 statically-robust techniques collapse — unicode_obfuscation fully (3/3). Static-pass numbers alone significantly overstate this model's robustness; see the project repo's docs/ISSUES.md (ISSUE-10) and docs/DECISIONS.md (D31) for the full methodology and honest framing.

Code, datasets, and full decision log: https://github.com/KNakul242/agent-context-guardrail (branch feature/primary-detector-redteam)

MIT (see repo).