> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fensu.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Read the Fensu Quickstart before onboarding a repository.
> Use fensu init --yes for an existing repository, or fensu init --yes --name NAME for an empty repository. Use --no-skills only when configuration-only initialization is explicitly required.
> Do not call Fensu onboarding complete until fensu skills --check succeeds.

# Overview

> Understand Fensu-shipped native policies, pack activation, namespaces, aliases, and execution.

Native rule packs are complete, Fensu-shipped policies for a particular framework
or architecture. They run in Rust like core rules, but stay out of the catalogue
until a repository explicitly activates them.

Use a native pack when Fensu ships an architecture policy that should replace the
generic core policy for that kind of repository. Packs can combine
framework-specific rules with transparent aliases of compatible core rules,
presenting one coherent namespace for selection, diagnostics, and generated
skills.

## Activation and selection

Pack activation and rule selection are separate:

```toml theme={null}
rule_packs = ["dagster"]
select = ["FPDG"]
```

* `rule_packs` controls which shipped catalogues are available.
* `select`, `warn`, and `ignore` assign available pack identities to policy tiers.
* Activating a pack does not select it.
* A pack selector matches no identities until its pack is activated.
* Pack names must be registered and unique.

This separation lets a repository activate a catalogue while selecting one rule,
one family of aliases, or the complete policy. The exact selectors belong to each
pack's reference page.

## Codes and namespaces

Fensu reserves `FP` for shipped native packs. Each pack owns a namespace beneath
that prefix. For example, the Dagster pack owns `FPDG`.

Pack-native rules append their numeric identity directly, such as `FPDG022`.
Retained core aliases preserve the core family and number after the pack namespace:
`FFA001` becomes `FPDGA001` in the Dagster pack.

An alias executes the canonical native implementation while diagnostics retain the
selected pack identity and disclose provenance:

```text theme={null}
FPDGA001 (alias FFA001)  function parameter 'value' must define a type annotation
```

The canonical code and its alias cannot occupy the same tier because that would
select one implementation twice. Fensu rejects the overlap instead of emitting
duplicate diagnostics.

## Native execution

Pack-native rules and retained aliases execute without starting Python. They use
the same deterministic discovery, caching, warning, ignore, exception, and output
machinery as core rules.

Activating a native pack by itself does not require a Python interpreter. A project
that also configures `rule_paths`, `rule_modules`, or custom-rule options still
uses the custom-rule metadata host for those custom rules.

[`fensu rule`](/cli/rule) shows `Kind: pack`, the owning pack, and any canonical
alias target for an activated identity.

## Available packs

<CardGroup cols={2}>
  <Card title="Dagster" icon="diagram-project" href="/concepts/rule-packs/dagster">
    A standalone Dagster repository architecture with 23 native policies and 100
    retained core aliases.
  </Card>
</CardGroup>