/**
 * Sentinel-based "this value must be filled in before deploy" marker.
 *
 * Use `todo(reason)` in `defaults` or any `perEnv` branch to declare a
 * slot you'll fill in later. The loader scans the merged config before
 * calling `build()`; if any sentinel survives the merge for the env
 * being loaded, it throws `NodeSettingsError` with code `PER_ENV_TODO`.
 *
 * @example
 * ```ts
 * import { defineSettings, todo } from "@env-kit/node-settings";
 *
 * defineSettings({
 *   envSchema, envKey: "APP_ENV",
 *   defaults: { bucket: "" },
 *   perEnv: {
 *     local: { bucket: "local-bucket" },
 *     prod:  { bucket: todo("set production bucket name before deploy") },
 *   },
 *   build: (env, config) => ({ bucket: config.bucket }),
 * });
 *
 * settings({ APP_ENV: "local", ... }); // ok
 * settings({ APP_ENV: "prod",  ... }); // throws NodeSettingsError (PER_ENV_TODO)
 * ```
 *
 * Sentinels behave as opaque values inside `deepMerge` — a child
 * `perEnv` branch can fully replace a parent's sentinel with a real
 * value. This means `defaults: { bucket: todo("...") }` is a useful
 * pattern: every per-env branch is *forced* to provide a value.
 */
/**
 * Globally registered symbol that marks an object as a todo sentinel.
 * Using `Symbol.for(...)` keeps the marker stable across module
 * boundaries (e.g. mixed CJS / ESM situations).
 */
export declare const TODO_SYMBOL: unique symbol;
/** Runtime shape of a todo sentinel. */
export interface TodoSentinel {
    readonly [k: symbol]: unknown;
    readonly reason: string;
    /**
     * Custom `toJSON` so `JSON.stringify(config)` produces a readable
     * marker (`{ "$todo": "reason" }`) instead of an opaque object.
     * Honored automatically by `JSON.stringify`.
     */
    readonly toJSON: () => {
        $todo: string;
    };
}
/**
 * Mark a config field as "not yet set; must be filled in before the
 * env that contains it can be loaded".
 *
 * Typed as returning `never` so the result is assignable to any field
 * type. At runtime it returns a sentinel object that the loader,
 * `deepMerge`, `checkPerEnvCompleteness`, and the `inspect` CLI all
 * recognise.
 */
export declare function todo(reason?: string): never;
/** True when `value` is a `todo(...)` sentinel. */
export declare function isTodo(value: unknown): value is TodoSentinel;
/**
 * Recursively scan `value` for any `todo(...)` sentinels and return
 * their locations. Used by both the loader (to throw before build)
 * and the `check` CLI (to report across every perEnv branch).
 */
export declare function findTodos(value: unknown, path?: string): Array<{
    path: string;
    reason: string;
}>;
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