# `DEFAULT_INTERPOLATION` — interpolation engine defaults

## Purpose

`DEFAULT_INTERPOLATION` is the canonical default configuration for the
ICU interpolation engine that ships with `@suaveplan/i18n-icu-parser`
(Wave 2 of the modular split). Centralising the defaults here lets
every leaf package — the parser, the catalog, the slim core, even
custom plugins — agree on the same delimiter pair and nesting limit
without re-declaring the literals. Consumers that want to override
the defaults can spread them at construction time
(`{ ...DEFAULT_INTERPOLATION, prefix: "${" }`); the immutable shape
ensures no consumer can accidentally mutate the defaults at module
init.

## Features

- Mustache-compatible delimiters (`{{` / `}}`) — drop-in for catalogs
  authored against any popular i18n format
- `maxDepth: 10` ceiling — short-circuits pathological recursion
- `as const` shape — string literals narrow at the type level for
  branded types
- Frozen at module-init via `as const` — no consumer can mutate

## Usage: Basic Example

```ts
import { DEFAULT_INTERPOLATION } from "@suaveplan/i18n-shared";

const prefix = DEFAULT_INTERPOLATION.prefix;   // "{{"
const suffix = DEFAULT_INTERPOLATION.suffix;   // "}}"
const maxDepth = DEFAULT_INTERPOLATION.maxDepth; // 10
```

## Usage: Advanced Example

```ts
import { DEFAULT_INTERPOLATION } from "@suaveplan/i18n-shared/constants/interpolation-defaults";

// Override the prefix / suffix while keeping the depth limit
const customDelimiters = {
    ...DEFAULT_INTERPOLATION,
    prefix: "${",
    suffix: "}",
} as const;

// Pass the custom shape to the interpolation engine (parser package
// will accept this shape verbatim)
const interpolation = customDelimiters; // type-narrowed
```

## API Reference

### `DEFAULT_INTERPOLATION`

Frozen object literal with these fields:

| Field | Type | Value |
|---|---|---|
| `prefix` | `"{{"` | Opening placeholder delimiter |
| `suffix` | `"}}"` | Closing placeholder delimiter |
| `maxDepth` | `10` | Maximum nested-resolution depth |

Throws: nothing — read-only constant.

## Implementation Notes

- The choice of `{{` / `}}` matches Mustache, Handlebars, and i18next
  out of the box. Catalogs authored against any of those tools load
  without rewriting placeholders.
- The `maxDepth` of 10 is empirical — pathological self-referencing
  catalogs (`{"a": "{{a}}"}`) are detected within 10 expansions
  while well-formed nested-key cases (rare beyond depth 3) still
  complete normally.
- The shape is `as const` (NOT a Zod schema) because every consumer
  of this constant treats it as the authoritative literal — there is
  no boundary parsing required at this layer.