/**
 * Observer-drop optimization.
 *
 * At config-build time, observers whose declared `writes: [...]` are
 * entirely unconsumed by any rule's `happened.event` / `happened.since`
 * can be dropped: they'd only fire on `tool_result` and write entries
 * no rule ever reads. Dropping them skips both the write (cheaper
 * session JSONL) and the speculative-synthesis contribution (no chain
 * entries for events nobody consults).
 *
 * Observers with `writes === undefined` or `writes: []` are kept
 * unconditionally — without a declaration we can't prove they're
 * unused, and `[]` is conservative parity with undeclared. Plugin
 * authors are encouraged to declare `writes` both for this
 * optimization and for `defineConfig`'s compile-time type inference.
 *
 * Pure function — no logging. Callers (session-runtime, testing)
 * log on drop so tests can inspect `dropped` directly without
 * intercepting stdout.
 */
import type { Observer, Rule } from "../schema.ts";
/** An observer dropped by {@link dropUnusedObservers}. */
export interface DroppedObserver {
    readonly name: string;
    readonly writes: readonly string[];
    readonly reason: "unused-writes";
}
/**
 * Partition `observers` into kept and dropped based on whether each
 * observer's declared writes are consumed by any rule.
 *
 * @param observers - Observers to filter (any origin — plugin-merged
 *   or user-authored).
 * @param rules - Full rule set whose `happened.event` / `happened.since`
 *   references determine consumption. Disabled rules should already
 *   be filtered out by the caller — this helper honors whatever's
 *   passed in.
 */
export declare function dropUnusedObservers(observers: readonly Observer[], rules: readonly Rule[]): {
    kept: readonly Observer[];
    dropped: readonly DroppedObserver[];
};
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