/**
 * Per-page-load capability cache — the entire backward-compat story for a
 * mixed-version rollout. Each capability starts `unknown`; a successful use flips
 * it `supported`, a "Cannot query field" / 404 flips it `unsupported`. No
 * coordinated feature flags: the FE simply degrades (delta→full poll,
 * long-poll→2s poll, SSE→poll) against an older backend, and lights up
 * automatically once the backend advertises the capability.
 */
export type CapabilityState = 'unknown' | 'supported' | 'unsupported';
interface AssistantCapabilities {
    waitForSandboxRunning: CapabilityState;
    sinceParam: CapabilityState;
    sse: CapabilityState;
}
export declare function getCapability(key: keyof AssistantCapabilities): CapabilityState;
export declare function markSupported(key: keyof AssistantCapabilities): void;
export declare function markUnsupported(key: keyof AssistantCapabilities): void;
/** True when an error indicates the server doesn't know a field/route yet. */
export declare function isUnknownFieldError(error: unknown): boolean;
export {};
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