/**
 * Subagent session-log reader — turns a background agent's on-disk session
 * JSONL into the message list the client's transcript reducer consumes.
 *
 * Why disk: `background_agent_event` relays are ephemeral (they exist only on
 * SSE clients connected while the agent streams). After a browser reload the
 * reducer state is gone, so the session log is the only source of truth for
 * a subagent transcript. The child process appends entries as it works, so
 * reading the file mid-run yields the transcript up to the last completed
 * message.
 */
export interface SubagentLogSource {
    /** Path to the agent's session JSONL (known after the child exits). */
    sessionFile?: string;
    /** Directory the child writes its session into (known at spawn time). */
    sessionDir?: string;
}
export declare class SubagentSessionLogNotFoundError extends Error {
    constructor();
}
/**
 * Find chain step session JSONLs under step-N/ directories, ordered by numeric
 * step index. Returns an empty list for missing/non-chain directories.
 */
export declare function discoverSubagentStepSessionFiles(sessionDir: string): string[];
/**
 * Find the most recently modified .jsonl in a session directory. Parity with
 * discoverSessionFile in @dreb/coding-agent's subagent tool. Normal subagents
 * write directly under sessionDir; chain-mode subagents register the chain root
 * but write per-step logs under step-N/ subdirectories.
 */
export declare function discoverSubagentSessionFile(sessionDir: string): string | undefined;
/**
 * Read the message payloads from a subagent session log.
 *
 * Subagent sessions are single-shot and linear (no branching/compaction), so
 * a straight scan of `type: "message"` entries reconstructs the transcript.
 * Chain-mode subagents write one linear log per step; those step logs are
 * concatenated in numeric step order. Malformed lines are skipped (the tail
 * line can be mid-write).
 *
 * @throws when no session file can be located — callers surface this loudly.
 */
export declare function readSubagentMessages(source: SubagentLogSource): unknown[];
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