return { dir, file: path.join(dir, "session.jsonl") };

}

function requireBackupPath(result: { backupPath?: string }): string {

if (!result.backupPath) {

throw new Error("expected session repair backup path");

}

return result.backupPath;

async function expectNoRetainedBackup(

file: string,

result: { backupPath?: string },

): Promise<void> {

expect(result.backupPath).toBeUndefined();

const siblings = await fs.readdir(path.dirname(file));

const leftover = siblings.filter((name) => name.includes(".bak-"));

expect(leftover).toEqual([]);

}

function requireFirstLogMessage(log: ReturnType<typeof vi.fn>): string {

const result = await repairSessionFileIfNeeded({ sessionFile: file });

expect(result.repaired).toBe(true);

expect(result.droppedLines).toBe(1);

const backupPath = requireBackupPath(result);

const repaired = await fs.readFile(file, "utf-8");

const repairedLines = repaired

.map((line) => JSON.parse(line));

expect(repairedLines).toEqual([header, message]);

const backup = await fs.readFile(backupPath, "utf-8");

expect(backup).toBe(content);

await expectNoRetainedBackup(file, result);

});

it("does not accumulate backups across repeated repairs of a persistently corrupted file", async () => {

// Regression for #80960: a stuck session with a writer that keeps

// appending a malformed line caused every repair invocation to leave a

// ~1.8 MB `.bak-<pid>-<ts>` snapshot, accumulating 2,180 files / 2.1 GB

// on a single agent over ~25 hours.

const { file } = await createTempSessionPath();

const { header, message } = buildSessionHeaderAndMessage();

const malformedTail = '{"type":"message"';

for (let i = 0; i < 5; i++) {

const content = `${JSON.stringify(header)}\n${JSON.stringify(message)}\n${malformedTail}`;

await fs.writeFile(file, content, "utf-8");

const result = await repairSessionFileIfNeeded({ sessionFile: file });

expect(result.repaired).toBe(true);

expect(result.droppedLines).toBe(1);

await expectNoRetainedBackup(file, result);

}

});

it("does not drop CRLF-terminated JSONL lines", async () => {

expect(result.repaired).toBe(true);

expect(result.droppedLines).toBe(0);

expect(result.rewrittenAssistantMessages).toBe(1);

await expect(fs.readFile(requireBackupPath(result), "utf-8")).resolves.toBe(original);

await expectNoRetainedBackup(file, result);

expect(debug).toHaveBeenCalledTimes(1);

const debugMessage = requireFirstLogMessage(debug);

expect(debugMessage).toContain("rewrote 1 assistant message(s)");

expect(result.repaired).toBe(true);

expect(result.insertedToolResults).toBe(1);

const backup = await fs.readFile(requireBackupPath(result), "utf-8");

expect(backup).toBe(original);

await expectNoRetainedBackup(file, result);

const lines = (await fs.readFile(file, "utf-8")).trimEnd().split("\n");

expect(lines).toHaveLength(5);

expect(result.repaired).toBe(true);

expect(result.droppedLines).toBe(3);

await expect(fs.readFile(requireBackupPath(result), "utf-8")).resolves.toBe(`${content}\n`);

await expectNoRetainedBackup(file, result);

const after = await fs.readFile(file, "utf-8");

const lines = after.trimEnd().split("\n");