# MatchAst.Layer

A Match AST boundary carrying route-local Effect Layers.

## Signatures

```ts
interface Layer {
    type: "layer";
    matches: ReadonlyArray<MatchAst>;
    deps: ReadonlyArray<AnyLayer>;
}
```

## Why

Dependencies can be prepared, committed, rolled back, and finalized with candidate selection.

## Ownership and lifetime

`Layer` describes plain readonly AST data. Routes and Matchers retain the concrete nodes they receive by reference; the type itself owns no resource.

## Property: deps

The Effect Layers attached to a matcher subtree.

## Property: deps: Why

Candidate services and their failures stay explicit during preparation and rollback.

## Property: deps: Ownership and lifetime

Layer values are retained by identity. The executor's Layer manager, not the AST, owns their
acquired child Scopes and rollback.

## Property: matches

The ordered child matcher nodes wrapped by this boundary.

## Property: matches: Why

Order is preserved for candidate and guard fallthrough.

## Property: matches: Ownership and lifetime

The Layer boundary retains this ordered child array by reference so compilation preserves
same-path candidate fallthrough.

## Property: type

The discriminant identifying this AST variant.

## Property: type: Why

Exhaustive switches can interpret syntax without instanceof checks or hidden classes.