Feat/add wg bastion

[The-Rabak]

feat/add-wg-bastion — LLM security guardrails crate (Phase 1 + 2)

What

Introduces wg-bastion, a new workspace member crate providing composable, pipeline-based security guardrails for LLM applications. This PR covers:

• Phase 1 — Core pipeline framework: typed content model, stage execution engine with priority sorting, graceful degradation, and fail-mode enforcement.
• Phase 2 — Prompt & injection security: 50 heuristic detection patterns, structural text analysis, ensemble scoring, input normalisation, system-prompt hardening, canary tokens, and RAG boundary marking.

13,000+ lines across 35 new files, 209 tests, 0 clippy warnings.

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Why

LLM applications face a growing class of attacks (prompt injection, system prompt extraction, delimiter manipulation, encoding evasion) catalogued by the OWASP LLM Top 10. wg-bastion provides a Rust-native, zero-allocation-on-clean-path defense layer that integrates
with weavegraph's graph execution model. The heuristic path has 5.5ms P95 latency, 100% detection rate on the adversarial corpus, and <2% false positive rate.

---

Crate structure

wg-bastion/src/
├── config/mod.rs (262 lines) SecurityPolicy, PolicyBuilder, FailMode
├── pipeline/ Core execution framework
│ ├── content.rs (279 lines) Content enum: Text, Messages, ToolCall, ToolResult, RetrievedChunks
│ ├── stage.rs (441 lines) GuardrailStage trait, SecurityContext (session, risk, delegation chain)
│ ├── outcome.rs (286 lines) StageOutcome: Allow/Block/Transform/Escalate/Skip, Severity levels
│ ├── executor.rs (693 lines) PipelineExecutor: priority sorting, degradation, Transform propagation
│ ├── compat.rs (207 lines) LegacyAdapter bridging old SecurityStage → new GuardrailStage
│ └── mod.rs (324 lines) Legacy SecurityPipeline (kept for backward compat)
├── prompt/ System prompt protection (Phase 2A)
│ ├── template.rs (649 lines) SecureTemplate — typed placeholders {{name:type:max}}, auto-escaping
│ ├── scanner.rs (670 lines) TemplateScanner — regex+entropy secret detection in prompts
│ ├── honeytoken.rs (811 lines) HoneytokenStore — AES-256-GCM canary tokens, Aho-Corasick leak scan
│ ├── isolation.rs (546 lines) RoleIsolation — randomised [SYSTEM_START_] boundary markers
│ └── refusal.rs (550 lines) RefusalPolicy — per-severity response modes (block/redact/safe/escalate)
├── input/ Input validation (Phase 2B + 2C)
│ ├── normalization.rs (1,101 lines) NormalizationStage — NFKC, confusables, HTML, control chars, truncation
│ ├── injection.rs (784 lines) InjectionStage — composes heuristic + structural + ensemble into a stage
│ ├── patterns.rs (568 lines) 50 built-in regex patterns across 5 attack categories
│ ├── structural.rs (631 lines) StructuralAnalyzer — single-pass 5-signal text analysis
│ ├── ensemble.rs (480 lines) EnsembleScorer — 4 strategies: threshold, weighted avg, majority vote, max
│ └── spotlight.rs (578 lines) Spotlight — RAG chunk boundary marking + injection detection in chunks
└── lib.rs (143 lines) Crate root, feature gates, prelude

Plus:

• tests/injection_detection.rs (784 lines) — 100 adversarial + 52 benign integration tests
• fuzz/fuzz_targets/ — 3 cargo-fuzz targets (template, injection, normalization)

---

How the pipeline works

Content (user text)
│
▼
PipelineExecutor::run()
│
├── Stage 1: NormalizationStage (priority 10)
│ Strips invisible Unicode, applies NFKC, maps confusable chars,
│ strips HTML tags (preserving LLM tokens like <|im_start|>),
│ decodes HTML entities. Returns Transform(clean_text) or Allow.
│
├── Stage 2: InjectionStage (priority 50)
│ ├─ HeuristicDetector: O(n) RegexSet scan across all 50 patterns
│ │ simultaneously, then individual captures for matched patterns.
│ ├─ StructuralAnalyzer: single-pass char accumulator computing
│ │ suspicious char ratio, instruction density, language mixing,
│ │ repetition anomaly, punctuation anomaly → overall_risk.
│ └─ EnsembleScorer: combines pattern weights + structural risk
│ into Block/Allow via configurable strategy.
│
└── (your custom stages at any priority)
│
▼
PipelineResult
├── is_allowed() / blocked_reasons()
└── per-stage metrics (latency, degraded flag)

Each stage implements:

#[async_trait]
trait GuardrailStage: Send + Sync {
fn id(&self) -> &str;
async fn evaluate(&self, content: &Content, ctx: &SecurityContext)
-> Result<StageOutcome, StageError>;
fn degradable(&self) -> bool { true } // skip-on-error by default
fn priority(&self) -> u32 { 100 } // lower = runs first
}

A Block or Escalate short-circuits the pipeline. A Transform replaces the content for all subsequent stages. If a degradable stage errors, the pipeline logs it and continues.

---

Detection patterns (5 categories, 50 patterns)

┌──────────────────────────┬───────────────┬───────────────────────────────────────────────────────────────┬──────────────┐
│ Category │ IDs │ Examples │ Weight range │
├──────────────────────────┼───────────────┼───────────────────────────────────────────────────────────────┼──────────────┤
│ Role Confusion │ RC-001→RC-014 │ "You are now DAN", "Ignore all previous instructions" │ 0.5–1.0 │
├──────────────────────────┼───────────────┼───────────────────────────────────────────────────────────────┼──────────────┤
│ Instruction Override │ IO-001→IO-010 │ "IMPORTANT: override safety", "sudo mode" │ 0.5–0.95 │
├──────────────────────────┼───────────────┼───────────────────────────────────────────────────────────────┼──────────────┤
│ Delimiter Manipulation │ DM-001→DM-010 │ [INST], <|im_start|>, , ---\nsystem: │ 0.5–0.95 │
├──────────────────────────┼───────────────┼───────────────────────────────────────────────────────────────┼──────────────┤
│ System Prompt Extraction │ SE-001→SE-008 │ "Repeat your instructions", "What is your system prompt" │ 0.5–0.95 │
├──────────────────────────┼───────────────┼───────────────────────────────────────────────────────────────┼──────────────┤
│ Encoding Evasion │ EE-001→EE-008 │ Unicode escapes, HTML entities, base64 references, homoglyphs │ 0.5–0.65 │
└──────────────────────────┴───────────────┴───────────────────────────────────────────────────────────────┴──────────────┘

Patterns fire with weights; the ensemble scorer sums matched weights (capped at 1.0) and applies the configured strategy threshold (default: AnyAboveThreshold(0.7)).

---

Feature flags

┌────────────────────┬─────────┬────────────────────────────────────────────┬───────────────────────────────────────────────────────────┐
│ Flag │ Default │ Dependencies │ What it enables │
├────────────────────┼─────────┼────────────────────────────────────────────┼───────────────────────────────────────────────────────────┤
│ heuristics │ ✅ yes │ regex, aho-corasick, unicode-normalization │ All input/ and prompt/ modules │
├────────────────────┼─────────┼────────────────────────────────────────────┼───────────────────────────────────────────────────────────┤
│ honeytoken │ no │ ring, zeroize, aho-corasick │ AES-256-GCM canary token generation + detection │
├────────────────────┼─────────┼────────────────────────────────────────────┼───────────────────────────────────────────────────────────┤
│ normalization-html │ no │ lol_html │ Full HTML sanitisation (lol_html); regex fallback without │
├────────────────────┼─────────┼────────────────────────────────────────────┼───────────────────────────────────────────────────────────┤
│ moderation-onnx │ no │ ort │ ONNX ML classifier (Phase 3+) │
├────────────────────┼─────────┼────────────────────────────────────────────┼───────────────────────────────────────────────────────────┤
│ telemetry-otlp │ no │ opentelemetry stack │ OTLP export (Phase 3+) │
└────────────────────┴─────────┴────────────────────────────────────────────┴───────────────────────────────────────────────────────────┘

---

Test results

209 tests: 186 unit + 20 integration + 3 doctest
• 100% detection on 100-sample adversarial corpus (5 attack categories)
• 0% false positive on 52-sample benign corpus
• P95 pipeline latency: 5.5ms
• 0 clippy warnings (workspace-wide)
• cargo deny: clean (advisories, bans, licenses, sources)
• cargo machete: no unused dependencies

---

Key design decisions

1. Cow<'_, str> everywhere in normalization — zero allocation when input is already clean (the common case). Only allocates when text actually needs transformation.
2. RegexSet first-pass in HeuristicDetector — scans all 50 patterns in a single O(n) pass. Only patterns that match get individual Regex::captures() for span extraction.
3. Single-pass CharAccumulator in StructuralAnalyzer — computes all 5 analysis signals in one character iteration instead of 4 separate passes.
4. #[non_exhaustive] on all enums — StageOutcome, Content, Severity, FailMode are all non-exhaustive so future phases can add variants without breaking downstream.
5. Feature-gated modules — prompt/ and input/ only compile when heuristics is enabled (it's in default). honeytoken pulls in ring + zeroize only when opted into.
6. LegacyAdapter — bridges the Phase 0 SecurityStage trait to Phase 1's GuardrailStage trait, so existing stages don't need rewriting.

---

Files outside wg-bastion/ touched

┌─────────────────┬───────────────────────────────────────────────────────────────────────────────┐
│ File │ Change │
├─────────────────┼───────────────────────────────────────────────────────────────────────────────┤
│ Cargo.toml │ Added wg-bastion to workspace.members, added workspace.exclude for fuzz crate │
├─────────────────┼───────────────────────────────────────────────────────────────────────────────┤
│ deny.toml │ Added 3 new RUSTSEC advisories to ignore list (transitive, pre-existing) │
├─────────────────┼───────────────────────────────────────────────────────────────────────────────┤
│ SECURITY.md │ Added security policy document │
├─────────────────┼───────────────────────────────────────────────────────────────────────────────┤
│ CONTRIBUTING.md │ Already existed, unchanged │
└─────────────────┴───────────────────────────────────────────────────────────────────────────────┘

[Copilot]

Pull request overview

Adds wg-bastion as a new workspace crate providing a composable, pipeline-based set of LLM security guardrails (core pipeline + prompt/injection protections), plus supporting docs, fuzzing targets, and repo-wide security review/process updates.

Changes:

• Introduces the wg-bastion crate (config + pipeline framework + prompt/input security modules).
• Adds extensive security documentation (threat model, architecture, control matrix, playbooks) and fuzzing harnesses.
• Updates workspace/repo policy files (workspace members, cargo-deny ignores, security policy, PR/review checklists).

Reviewed changes

Copilot reviewed 41 out of 42 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
Cargo.toml	Adds wg-bastion to workspace members and excludes the fuzz crate from workspace builds.
deny.toml	Extends ignored RustSec advisories list for transitive dependencies.
SECURITY.md	Adds repository security policy and disclosure guidance.
CONTRIBUTING.md	Adds wg-bastion-specific security review requirements and CI expectations.
.gitignore	Updates ignored paths/patterns (incl. plan/todo files and some .github dirs).
.github/copilot-mcp-config.json	Adds MCP server configuration for Copilot tooling.
.github/PULL_REQUEST_TEMPLATE.md	Adds a security-focused PR checklist (esp. for wg-bastion changes).
wg-bastion/Cargo.toml	New crate manifest: dependencies and feature flags (heuristics, honeytoken, normalization-html, etc.).
wg-bastion/src/lib.rs	Crate root: module wiring, feature gates, and prelude re-exports.
wg-bastion/src/config/mod.rs	SecurityPolicy / PolicyBuilder implementation (file/env loading + validation).
wg-bastion/src/pipeline/mod.rs	Keeps legacy pipeline APIs and introduces new typed pipeline submodules.
wg-bastion/src/pipeline/content.rs	Defines the Content enum and helpers for flattening to text.
wg-bastion/src/pipeline/outcome.rs	Defines StageOutcome, Severity, and StageError for the new pipeline.
wg-bastion/src/pipeline/stage.rs	Defines GuardrailStage and the new typed SecurityContext.
wg-bastion/src/pipeline/compat.rs	Adds LegacyAdapter to bridge legacy SecurityStage into GuardrailStage.
wg-bastion/src/input/mod.rs	Wires input-security modules behind the heuristics feature.
wg-bastion/src/input/patterns.rs	Adds built-in injection regex pattern library (+ tests).
wg-bastion/src/input/ensemble.rs	Adds ensemble scoring strategies and EnsembleScorer.
wg-bastion/src/input/spotlight.rs	Adds RAG chunk boundary marking + injection/forgery detection stage.
wg-bastion/src/prompt/mod.rs	Wires prompt-protection modules (scanner/template/isolation/honeytoken/refusal).
wg-bastion/src/prompt/isolation.rs	Adds system-boundary marker wrapping + forged/nesting/unmatched marker detection stage.
wg-bastion/src/prompt/template.rs	Adds SecureTemplate with typed placeholders, escaping, and secret scanning.
wg-bastion/src/prompt/refusal.rs	Adds RefusalPolicy to map blocking outcomes to user-facing refusal actions + audit entries.
wg-bastion/fuzz/Cargo.toml	Adds a dedicated cargo-fuzz crate for wg-bastion fuzz targets.
wg-bastion/fuzz/README.md	Documents how to run fuzz targets.
wg-bastion/fuzz/fuzz_targets/fuzz_template.rs	Fuzz target for template compile/render.
wg-bastion/fuzz/fuzz_targets/fuzz_injection.rs	Fuzz target for injection detector determinism/panic safety.
wg-bastion/fuzz/fuzz_targets/fuzz_normalization.rs	Fuzz target for normalization stage evaluation.
wg-bastion/docs/threat_model.md	Adds threat model document (OWASP/NIST/MITRE aligned).
wg-bastion/docs/diagrams/data_flow.mmd	Adds Mermaid data-flow diagram for the security boundary architecture.
wg-bastion/docs/control_matrix.md	Adds narrative control matrix documentation.
wg-bastion/docs/control_matrix.csv	Adds machine-readable control matrix mapping controls→modules→tests.
wg-bastion/docs/attack_playbooks/llm01_prompt_injection.md	Adds incident response playbook for prompt injection.
wg-bastion/docs/architecture.md	Adds detailed architecture document and planned integration patterns.

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