upstream PR #15684: project file attachment: a failed hold release leaves the attached file's upload TTL armed #18

Follow-up from LibreChat-AI#15684. Originally filed as LibreChat-AI#15804 (to be closed there; follow-ups live on this fork).

What happens

addChatProjectFile associates a file with a Chat Project through one atomic
findOneAndUpdate (capacity guarded), and only afterwards clears the upload
hold on the file document:

// packages/data-schemas/src/methods/chatProject.ts
const updated = await ChatProject.findOneAndUpdate(
  { _id: project._id, user, file_ids: { $ne: fileId },
    [`file_ids.${MAX_CHAT_PROJECT_FILES - 1}`]: { $exists: false } },
  { $addToSet: { file_ids: fileId }, $inc: { contextRevision: 1 } },
  ...
);
if (updated) {
  await releaseTemporaryHold();   // $unset expiresAt, temp_file_id
  return updated;
}

That ordering is deliberate: a racer that loses the capacity guard must keep its
hold so the sweep can reclaim the upload (PR LibreChat-AI#15684). The two writes span two
collections without a transaction, so if the release write fails after the
association commits, the project keeps the reference while the file keeps
expiresAt — a MongoDB-managed one hour TTL (packages/data-schemas/src/schema/file.ts).
The request surfaces as a 500 from addProjectFile, and the file can be deleted
underneath a project that still lists it.

Why it is not already broken

An idempotent re-add repairs it: the atomic update no-ops, the fresh read finds
the file already associated, and the release is retried
(chatProject.ts, fresh-current branch). The client retries the association on
its failed row, so the common path self-heals. A user who never retries keeps a
project reference that resolves as unavailable after the TTL fires.

Suggested direction

Compensate the release rather than relying on a retry: bounded inline retry, or
a reconciliation pass that clears holds on files already referenced by a project
(the sweep is expiredAt-driven and does not look at project membership). Worth
a regression that forces the release write to fail and asserts the file does not
stay TTL-armed.

Found while auditing PR LibreChat-AI#15684; no regression covers this window today.