/**
 * Which extension to WRITE a generated test with.
 *
 * Convention first, configuration only to disagree — the Rails/Next posture the
 * rest of this rule already takes. A project that looks like TypeScript gets a
 * `.ts` test without being asked; the config field exists for the cases detection
 * cannot get right (a monorepo with mixed packages, a JS project carrying a
 * stray `tsconfig.json`, a deliberate choice to keep tests in JS).
 *
 * 🔴 THE FIELD IS NOT WRITTEN BY `init`, ON PURPOSE. A value recorded at
 * initialisation is a decision that goes stale in silence: the project migrates to
 * TypeScript six months later and the config still says otherwise, with nobody
 * remembering it is there. Detection re-runs every time; the file stays empty
 * unless somebody actively disagrees, and an empty config means "I agree with all
 * of it".
 *
 * ## Why `.ts` and not `.mts`
 *
 * Measured on Node 22.22, both package kinds: a `.ts` file using `import` runs in
 * a package with `type: module` AND in one without it — type stripping detects
 * module syntax rather than trusting the package type. So the `.mts` special case
 * a careful reader expects here is not needed, and `.mts` stays what it is: a
 * file kind we ACCEPT (it is real, TS 4.7+) but never generate.
 *
 * ## Why `.mjs` and not `.js` for the non-TypeScript default
 *
 * `.js` in a package without `type: module` is CommonJS, and every generated test
 * uses `import`. `.mjs` is ESM regardless of the package, so the generated file
 * runs in a repo whose package.json nobody has touched.
 *
 * ## Why "looks like TypeScript" is not enough
 *
 * A suggestion is only worth making if `vigiles test` will RUN the file. Detection
 * used to stop at `tsconfig.json` / a `typescript` dependency and never ask whether
 * anything here can execute a `.ts` script — so on Node 20 (this repo's own CI) in a
 * project without `tsx`, the finding said "add `foo.harness.ts`" and the runner then
 * threw `Cannot run TypeScript test script`. The `canRunTypeScript` signal closes
 * that: a MEASURED `false` falls back to `.mjs`, which runs everywhere.
 *
 * Pure: signals in, an extension out. No filesystem — the two engines (disk and
 * browser) each gather the signals their own way and cannot drift on the decision.
 */
export interface TestExtSignals {
    /** `testExtension` from `.vigilesrc.json`, when the author disagreed. */
    readonly configured?: string | undefined;
    /** A `tsconfig.json` at the scan root. */
    readonly hasTsconfig: boolean;
    /** Raw `package.json` text, or undefined. Scanned for a `typescript` dependency
     *  — parsed leniently on purpose: a malformed package.json is another rule's
     *  finding, and this decision must not throw on it. */
    readonly packageJson?: string | undefined;
    /**
     * Can `vigiles test` actually EXECUTE a TypeScript script here — is `tsx`
     * installed, or does Node strip types natively (>= 22.6)? The same disjunction
     * the runner branches on; see `src/ts-runner-caps.ts#canRunTypeScript`.
     *
     * 🔴 A MEASURED `false` OVERRIDES DETECTION. "This project is TypeScript" and
     * "this project can run a TypeScript test" are different questions, and only the
     * first was being asked. On Node 20 — which this repo's own CI still runs — a
     * project with a `tsconfig.json` and no local `tsx` was told to write
     * `foo.harness.ts`, and `interpreterArgs` then threw on the very file the
     * finding had asked for. A remedy the tool refuses to run is worse than silence:
     * the author does the work and is told no.
     *
     * `undefined` means NOBODY MEASURED, and absence of measurement is not evidence
     * of absence — the browser engine has no Node to ask, and a caller who never
     * looked must not silently downgrade every TypeScript repo to `.mjs`.
     */
    readonly canRunTypeScript?: boolean | undefined;
}
/**
 * The extension a generated test should use.
 *
 * An unrecognised `configured` value is IGNORED rather than honoured or thrown on:
 * writing `foo.harness.rb` because somebody typed `rb` would produce a file no
 * runner executes, and the untested finding would then point at a path that can
 * never satisfy it.
 */
export declare function testFileExt(signals: TestExtSignals): string;
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