export interface DevDiagnostics {
    /** True when a request path targets the structured last-error endpoint. */
    isLastErrorPath(pathname: string): boolean;
    /** The JSON body + headers for the last-error endpoint: the most recent failure, or a benign
     * `NIFRA_NONE` shape when nothing has failed yet. `no-store` so a stale failure is never cached. */
    lastError(): {
        readonly body: string;
        readonly headers: Readonly<Record<string, string>>;
    };
    /** Capture a thrown SSR failure: store it for the endpoint and return the overlay HTML. The overlay a
     * person sees and the JSON an agent reads come from this one Diagnostic, so they can never disagree. */
    capture(err: unknown, request: {
        readonly method: string;
        readonly url: string;
    }): string;
}
/** One diagnostics surface per dev server. `root` is the resolved project root; it scopes the codeframe
 * to the project (see buildDiagnostic). Both dev servers resolve a concrete root before calling this. */
export declare function createDevDiagnostics(root: string): DevDiagnostics;
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