# Permission and execution-policy guide

This directory owns the model-visible authorization decision for prepared tool
operations. It evaluates ordered rules, classifies shell authority, projects
and binds resources, enforces hard denials, brokers interactive approval, and
scopes persisted grants. Runtime confinement and backend selection remain
separate owners.

## Invariants and dependencies

- Rule evaluation is ordered and deterministic. Hard policy cannot be
  overridden by approval or remembered grants.
- Canonical resource binding must match the operation that eventually executes;
  reject resources that cannot be independently projected or revalidated.
- Headless execution fails closed when approval is required.
- Remembered grants are scoped to the exact supported resource/operation class.
  Broad/opaque shell authority and nonempty terminal input remain invocation-
  only where the current policy requires it.
- Shell wrappers, redirections, mutable project launchers, interpreters, and
  opaque command forms must retain their conservative classification.
- Approval authorizes a prepared invocation on the already-selected backend.
  It never changes Local/SSH/Podman selection and never claims to be a sandbox.
- Persistence of grants belongs to the store adapter; evaluation depends on a
  narrow grant interface rather than transport or UI types.

## Starting points

- `mod.rs` — public permission contracts and composition.
- `evaluation.rs` — ordered rule decision.
- `hard_policy.rs` / `opaque_policy.rs` — non-overridable and broad authority.
- `shell_parser.rs` / `command_classification.rs` — token/command semantics.
- `resource_projection.rs` / `resource_binding.rs` — prepared resource identity
  before and after approval.
- `broker.rs` — interactive request/reply lifecycle.
- `../store/permission_grants.rs` — durable remembered-grant adapter.
- `permissions_tests.rs` — sibling characterization suite.

## Verification

```sh
cargo test --locked -p nac-core permissions
cargo test --locked -p nac-core tools::kernel
make crate-check CRATE=nac-core
```

Add regressions for every new command/resource form, especially denial-before-
execution and approval/revalidation races.

## Generated artifacts and placement mistakes

Permission rules and projected resources are runtime contracts; this directory
owns no generated files. Persisted rule/grant compatibility is enforced by Rust
types, store migrations, and tests.

- Do not embed process execution, sandbox construction, HTTP approval DTOs, or
  frontend presentation in policy modules.
- Do not treat tool registration or visibility as an authorization grant.
- Do not persist a broad grant because a narrower argument happened to appear
  in one invocation.
- Do not weaken classification to make an unsupported shell syntax convenient;
  either bind it safely or fail closed.