/**
 * Minimal, idempotent INI / TOML key upserts for package-manager config files.
 *
 * These managers each own a small, hand-edited config file (`.npmrc`,
 * `pip.conf`/`pip.ini`, `.cargo/config.toml`). The harness must set exactly one
 * or two keys without clobbering the developer's other settings, so we parse the
 * file line-by-line and replace just the target line — re-running yields
 * byte-identical output (the second pass sees the key already present and
 * rewrites it in place).
 *
 * `.npmrc` is a flat `key=value` file (no sections); pip and cargo are sectioned
 * (`[global]`, `[http]`, `[net]`). One helper covers both: pass `section: null`
 * for the flat case. The caller supplies the exact value text and separator so
 * cargo's quoted TOML (`cainfo = "..."`) and pip's bare `cert=...` both render
 * faithfully.
 */
export interface UpsertIniOptions {
    /** Section header to scope the key under (e.g. `global`, `http`); null for a flat file. */
    section?: string | null;
    /** Separator between key and value. Default `=` (npm/pip); TOML uses ` = `. */
    separator?: string;
}
/**
 * Insert or update `key = value` in `existing`, preserving every other line.
 * When a `section` is given, the key is placed inside that section (created at
 * the end of the file if absent). Existing EOL style (CRLF vs LF) is preserved.
 */
export declare function upsertIniKey(existing: string, key: string, value: string, opts?: UpsertIniOptions): string;