/**

* Session trajectory tail command.

*

* It selects active or requested sessions, renders recent trajectory events,

* and can follow append-only trajectory files across rotation/truncation.

*/

import fs from "node:fs";

import path from "node:path";

import { readAcpSessionMeta } from "../acp/runtime/session-meta.js";

const FOLLOW_INTERVAL_MS = 1_000;

let followIntervalMsForTests: number | undefined;

/** Overrides the follow polling interval for tests. */

export function setSessionsTailFollowIntervalMsForTests(intervalMs?: number): void {

followIntervalMsForTests = intervalMs;

}

if (left.seq !== null && right.seq !== null && left.seq !== right.seq) {

return left.seq - right.seq;

}

// Some trajectory events lack sequence numbers; timestamp fallback keeps

// follow mode from replaying already-rendered events after file rewrites.

const byTimestamp = left.tsMs - right.tsMs;

if (byTimestamp !== 0) {

return byTimestamp;

return `prompt skipped${reason ? `: ${reason}` : ""}`;

}

case "tool.call":

// Tool arguments may contain secrets or user text; tail output shows only

// the tool name and a redacted placeholder.

return `${toolName(data)} {...redacted...}`;

case "tool.timeout":

return `${toolName(data)} timeout`;

const running = selections.filter((selection) => isRunningSession(selection));

if (running.length > 0) {

// Without an explicit key, prefer all running sessions so follow mode shows

// concurrent active work instead of only the newest store entry.

return running.toSorted(compareSelectionsByUpdatedAt);

}

fileState.size === state.offset && state.fileState?.mtimeMs !== fileState.mtimeMs;

if (replaced || truncated || possiblyRewrittenSameSize) {

// Log rotation, truncation, and same-size rewrites all require a full

// rescan; cursor filtering prevents duplicate event output.

const snapshot = readTrajectorySnapshot(state.selection.trajectoryPath);

state.fileState = snapshot.fileState;

state.offset = snapshot.offset;

state.offset = fileState.size;

state.fileState = fileState;

const combined = `${state.pending}${buffer.toString("utf8")}`;

// Keep an incomplete trailing JSON line until the next poll, matching

// append-only writers that flush in chunks.

const lines = combined.split(/\r?\n/u);

state.pending = lines.pop() ?? "";

return parseTrajectoryEventLines(lines);

return opts.sessionKey?.trim() ? resolveAgentIdFromSessionKey(opts.sessionKey) : undefined;

}

/** Tails recent trajectory events for the selected session(s). */

export async function sessionsTailCommand(

opts: SessionsTailOptions,

runtime: RuntimeEnv,