/**
 * Anti-overplanning system-prompt block for runaway-reasoning-prone models
 * (claude-fable-5, claude-opus-4-8). Port of transponder's reasoning-guard.mjs.
 *
 * Adaptive-thinking fable-5 can legally spend the entire output budget on a
 * single thinking block; Anthropic's own "Prompting Claude Fable 5" guide
 * ships tested anti-overplanning phrasing. The block is appended VERBATIM
 * AFTER caveman compression, so Anthropic's tested phrasing survives
 * byte-exact (it never passes through compressProse).
 */
export declare const REASONING_GUARD_MODEL_RE: RegExp;
/**
 * Kill switch: the guard is ON by default; `CURSOR_OPENCODE_REASONING_GUARD=0`
 * disables it. Read once per call so tests can flip env between cases.
 */
export declare function reasoningGuardEnabled(env?: Record<string, string | undefined>): boolean;
/**
 * The static anti-overplanning text block. Returned by reference so callers
 * can compare byte-exact without re-deriving it.
 */
export declare function reasoningGuardBlock(): string;
/**
 * Append the guard block to a (possibly caveman-compressed) system prompt when
 * the guard is enabled and the model is runaway-reasoning-prone. The block is
 * appended verbatim AFTER compression, separated by "\n\n", so the tested
 * phrasing survives byte-exact. Returns the input unchanged otherwise.
 */
export declare function withReasoningGuard(systemPrompt: string, modelId: string): string;