kernite 0.1.4

Contract-first policy decision CLI for deterministic decision + reason + trace.

Kernite

Kernite is an AI-operable policy engine for write-path enforcement. Use it as a Python library or run the OSS decision server.

It is purpose-built for one job: return a reproducible and machine-operable decision contract before any mutation call such as create, update, delete, or associate is executed.

Why Kernite

• Reason by Design: decision reasons are structured for programmatic remediation, not only human logs.
• Contract-First: decision, reason_codes, reasons, trace_hash are required integration surfaces.
• Reproducible tracing: canonical input and policy context produce deterministic trace_hash output.

Design Philosophy

• Zero overhead: no runtime dependencies (dependencies = []).
• Zero DSL: enforce your policy without learning a new language.
• Zero bypass: every write-mutation gets reviewed, every time.

See docs/design-philosophy.md for more information on design principles.

Compared with OPA/Cedar for AI Write Paths

Topic	Kernite	OPA/Cedar
Primary optimization	Machine remediation in write-path gating (reason_codes support fix-and-retry loops).	Human-authored policy ecosystems and policy-language tooling.
Decision contract	Required structured contract (decision, reason_codes, reasons, trace_hash).	Explanations exist, but the remediation contract is not standardized across integrations (codes/reasons/evidence vary by setup).
Reproducible evidence	Built-in deterministic evidence surface (trace_hash) plus conformance vectors for replay.	Strong policy engines; replay determinism depends on integration and policy/data pipeline discipline.

While OPA/Cedar/others are strong options for centralized policy-language workflows, Kernite is purpose-built for app-embedded, machine-operable, write-path enforcement with a stable response contract.

Non-goals

• A general-purpose policy language / DSL runtime.
• Proxying or routing traffic (Kernite returns decisions; your app performs the write).
• Replacing your domain logic. Kernite governs whether a write may proceed and why.

Install and Start

uvx kernite start

If you get invalid choice: 'start', your local CLI is an older release. Use one of:

uvx --from git+https://github.com/kerniteio/kernite kernite start

or:

uv tool install --upgrade kernite
kernite start

kernite start scaffolds a starter bundle at ./kernite/:

• policy.json
• execute-request.denied.json
• execute-request.approved.json
• guard.py
• README.md

kernite scaffold is an alias for the same command.

Run the OSS server:

uvx kernite serve

Run the starter flow:

cd kernite

curl -sS http://127.0.0.1:8000/v1/execute \
  -H 'content-type: application/json' \
  -H 'Idempotency-Key: readme-denied-001' \
  -d @execute-request.denied.json

curl -sS http://127.0.0.1:8000/v1/execute \
  -H 'content-type: application/json' \
  -H 'Idempotency-Key: readme-approved-001' \
  -d @execute-request.approved.json

Apply this write-path rule:

• mutate only when data.decision == "approved"
• when denied, branch on data.reason_codes for remediation/retry
• persist ctx_id, data.trace_hash, data.idempotency_key

Server endpoints:

• GET /health
• POST /execute
• POST /v1/execute
• POST /validate/execute
• POST /v1/validate/execute

/v1/execute is the versioned stability surface; /execute maps to the latest stable surface (currently v1 in this OSS server).

/execute and /v1/execute are the public decision endpoints. Each request always goes through:

1. payload validation and normalization
2. deterministic policy evaluation

Library Quick Start (Python)

from kernite import evaluate_execute

request = {
    "workspace_id": "workspace-demo",
    "principal": {"type": "token", "id": "api:ops-bot"},
    "object_type": "document",
    "operation": "create",
    "payload": {"title": "Q1 Plan"},
}
result = evaluate_execute(request, idempotency_key="req-001")

decision = result["data"]["decision"]
trace_hash = result["data"]["trace_hash"]  # persist with your write/audit record
reason_codes = result["data"]["reason_codes"]

Production Notes (OSS Reference Server)

• Authentication/authorization: the OSS reference server does not include built-in authn/authz. Run it behind your trusted boundary (for example mTLS, JWT verification, internal network policy, or API gateway auth).
• Request size/timeouts: the OSS reference server does not define built-in max body size or per-request timeout controls. Enforce size limits and timeouts at ingress/runtime (reverse proxy, gateway, or process supervisor).
• Logging/metrics: the OSS reference server is minimal by design (startup log only, request access logs suppressed by default). Add structured logs/metrics in your service wrapper or edge layer, and persist ctx_id/trace_hash from responses for audit evidence.

Quick Start: Execute

Request (governed scope with one policy, missing required title):

In v1, an allow policy is approved only if all its rules pass; any rule failure produces a denied decision with structured reasons.

{
  "workspace_id": "workspace-demo",
  "principal": {
    "type": "token",
    "id": "api:ops-bot"
  },
  "object_type": "document",
  "operation": "create",
  "payload": {},
  "policy_context": {
    "governed": true,
    "selected_policies": [
      {
        "policy_key": "document_create_default",
        "policy_version": 1,
        "effect": "allow",
        "rules": [
          {
            "rule_key": "require_title",
            "rule_definition": {
              "type": "required_fields",
              "fields": ["title"]
            },
            "reason_code": "missing_required_fields",
            "reason_message": "title is required."
          }
        ]
      }
    ]
  }
}

Response shape:

{
  "ctx_id": "ctx_...",
  "message": "Denied by governance policy.",
  "data": {
    "decision": "denied",
    "reason_codes": ["missing_required_fields"],
    "reasons": [
      {
        "code": "missing_required_fields",
        "message": "title is required.",
        "rule_key": "require_title",
        "field_path": "payload.title",
        "details": {
          "missing_fields": ["title"]
        }
      }
    ],
    "policy_selection_reason_code": "policy_selected_workspace_default",
    "policy": {
      "policy_key": "document_create_default",
      "policy_version": 1
    },
    "trace_hash": "sha256:...",
    "idempotency_key": "..."
  }
}

Happy-path response example (approved):

{
  "ctx_id": "ctx_...",
  "message": "Approved by governance policy.",
  "data": {
    "decision": "approved",
    "reason_codes": [],
    "reasons": [],
    "policy_selection_reason_code": "policy_selected_workspace_default",
    "policy": {
      "policy_key": "document_create_default",
      "policy_version": 1
    },
    "trace_hash": "sha256:...",
    "idempotency_key": "..."
  }
}

Contract invariants (v1):

• Required response fields: ctx_id, message, data, data.decision, data.reason_codes, data.reasons, data.policy_selection_reason_code, data.policy, data.trace_hash, data.idempotency_key.
• data.decision enum values are only approved or denied.
• message is human-readable (best-effort); integrations should branch on data.* fields, not message text.
• data.reason_codes and data.reasons may be empty arrays when data.decision is approved.
• When data.decision is denied, at least one data.reason_codes entry is present.
• data.trace_hash is stable across v1.x for the same canonicalized input and policy context.
• Canonicalization rule: Kernite deterministically canonicalizes all hash-participating arrays (for example sorted reason_codes and canonical policy-match entries used for hashing). This makes order-only differences in selected_policies/rules not change data.trace_hash.

Policy Context Model

policy_context is optional, but recommended for production integrations. Kernite evaluates the policies you provide in policy_context.selected_policies; in OSS mode it does not fetch policies from storage.

Main fields:

• governed (bool): whether this request must be enforced as governed scope.
• selected_policies (array): policies selected by your resolver.
• governed_scopes (array): optional scope list (object_type + operation) to infer governed status.
• policy_selection_reason_code (string): explicit selection reason, if already known.

Default behavior:

• governed + no selected policy => denied with no_matching_policy
• not governed + no selected policy => approved with out_of_scope_phase1

PARC Request Model

Kernite uses a Cedar-style PARC shape:

• principal
• action (operation)
• resource
• context

This keeps policy evaluation explicit and stable for relationship operations like associate.

See docs/parc-model.md for details and examples.

Use Cases (AI and Non-AI)

• AI-assisted actions: gate tool calls and use reason_codes for automatic retry/remediation.
• Internal APIs: apply one deterministic write guard across UI/API/workers.
• SaaS multi-tenant systems: enforce tenant-scoped write decisions and persist evidence.

See docs/use-cases.md for details and examples.

Compatibility and Conformance

• Contract policy: docs/compatibility.md
• Conformance vectors: docs/conformance/v1/execute_vectors.json
• Reason code semantics: docs/conformance/v1/reason_codes_v1.json

Objective Performance Check (Python)

Kernite includes a dependency-free benchmark harness.

uv run python benchmarks/benchmark_execute.py --iterations 20000

This gives p50/p95 latency and throughput from your actual environment so language/runtime decisions are based on measured data.

Latest measured snapshot is tracked in docs/performance.md.