expect(payload.lines.map((line) => line.message)).toEqual(["current sent"]);

});

it("returns the first line of the tail window when start aligns with a line boundary", async () => {

// MAX_BYTES in readTailLines is 1_000_000. We build a file of 2_000_000 bytes

// made of 10_000 lines each exactly 200 bytes (199 payload + "\n"), so the

// read window starts at byte offset 1_000_000 which is exactly on a line

// boundary (byte 999_999 is the trailing "\n" of the previous line).

// Without checking the byte before the window, readTailLines drops line 5000 silently.

const LINE_SIZE = 200;

const TOTAL_LINES = 10_000;

const FIRST_INDEX = 5000; // first line of the tail window after alignment

const buildLine = (message: string) => {

const base = logLine({

module: "gateway/channels/slack/send",

message,

});

const payloadLen = LINE_SIZE - 1; // reserve 1 byte for newline

// Re-emit with a padded message so total byte length is constant.

const padNeeded = payloadLen - Buffer.byteLength(base);

if (padNeeded < 0) {

throw new Error(`base log line too long: ${Buffer.byteLength(base)} > ${payloadLen}`);

}

const padded = logLine({

module: "gateway/channels/slack/send",

message: message + " ".repeat(padNeeded),

});

if (Buffer.byteLength(padded) !== payloadLen) {

throw new Error(`padded line wrong size: ${Buffer.byteLength(padded)} vs ${payloadLen}`);

}

return padded + "\n";

};

const handle = await fs.open(logPath, "w");

try {

for (let i = 0; i < TOTAL_LINES; i++) {

let message: string;

if (i === FIRST_INDEX) {

message = "first-line-in-window";

} else if (i === TOTAL_LINES - 1) {

message = "last-line";

} else {

message = "filler";

}

await handle.write(buildLine(message));

}

} finally {

await handle.close();

}

await channelsLogsCommand(

{ channel: "slack", json: true, lines: String(TOTAL_LINES) },

runtime,

);

const payload = readJsonPayload();

const messages = payload.lines.map((line) => line.message.trimEnd());

expect(messages[0]).toBe("first-line-in-window");

expect(messages[messages.length - 1]).toBe("last-line");

});

it("does not fall back to rolling logs for a missing custom log file", async () => {

const configuredFile = path.join(tempDir, "custom-channel.log");

const fallbackFile = path.join(tempDir, "openclaw-2026-04-25.log");