/**
 * Leaf type for agent runtime classification. Defined here so that
 * agent-runtime-metadata.ts can import applyAcpRuntimeOverlay without
 * creating a circular dependency (agent-runtime-metadata → acp-runtime-overlay
 * → agent-runtime-metadata).  agent-runtime-metadata.ts re-exports this type
 * so all existing consumers remain unaffected.
 */
export type AgentRuntimeMetadata = {
    id: string;
    source: "implicit" | "model" | "provider" | "session-key";
};
/**
 * When a session key and persisted session metadata identify an ACP
 * control-plane session, override the resolved runtime metadata to report the
 * ACP runtime id with a "session-key" source — regardless of what the
 * agent-config policy resolved to.
 *
 * Callers that already have model/provider context (resolveModelAgentRuntimeMetadata)
 * still benefit here because the model-runtime policy chain does not inspect session
 * keys for the ACP indicator.
 *
 * Key shape alone is not sufficient: ACP bridge sessions may use ACP-shaped
 * keys without persisted SessionAcpMeta and still run the configured model.
 *
 * When `acpBackend` is provided and non-empty, it is used as the runtime id so that
 * sessions backed by a configured non-default ACP backend (e.g. a custom registered
 * backend) are reported faithfully instead of always being labelled "acpx".
 * Falls back to "acpx" when no backend is known.
 */
export declare function applyAcpRuntimeOverlay(meta: AgentRuntimeMetadata, sessionKey: string | undefined | null, acpRuntime: boolean | undefined, acpBackend?: string): AgentRuntimeMetadata;