Provisioned sync fails on matrix.org: password change disabled, infinite spinner on desktop

[overcuriousity]

Hey there,

I tried to set up matrix sync, as synchronization between my devices would be a critical feature for me. It seems to only support matrix as a sync option, and as the docs were not exactly clear how to set it up, i let claude explain.
Following the steps, I ran into issues which are caused by incompatibility with the standard matrix.org homeserver. Also i failed to find an option to change the homeserver.

I would suggest adding a more general sync option like syncthing or file based sync like webdav/nextcloud.

Nonetheless, here is a bug report claude was kind enough to create for me, regarding the matrix issues:

Summary

Setting up sync using an existing matrix.org account fails with two bugs:

1. Android shows "Configuration failed" — matrix.org has disabled /_matrix/client/v3/account/password (returns M_UNRECOGNIZED). The Matrix SDK throws when it tries to rotate the password after joining the room, which lands in the outer catch block and surfaces as a generic configuration error.

2. Desktop shows infinite bare spinner — when provisioning completes (or fails) before the WoltModalSheet has finished mounting the config page (page index 1), the finally { link.close() } in configureFromBundle releases the keepAlive link. Riverpod auto-disposes the provider, and when page 1 mounts it gets a fresh initial state (bare CircularProgressIndicator with no label or progress bar) rather than the terminal state.

Steps to reproduce

1. Create a dedicated Matrix account on matrix.org
2. Use the tools/matrix_setup script (or craft a bundle manually) to create a sync room under that account
3. Paste the bundle string into Settings → Sync → Provisioned Sync → Configure
4. Android: see "Configuration failed" after a short delay
5. Desktop: see a bare loading spinner that never resolves

Root causes

Bug 1 (provisioning_controller.dart, configureFromBundle):

await matrixService.changePassword(
  oldPassword: bundle.password,
  newPassword: newPassword,
);

matrix.org returns M_UNRECOGNIZED for this endpoint. The exception propagates to the outer catch and sets ProvisioningError.configurationError, even though login and room join already succeeded.

Bug 2 (provisioning_controller.dart, configureFromBundle):

} finally {
  link.close();  // closes too early if provisioning finishes before page 1 mounts
}

Suggested fix

Bug 1: Wrap changePassword in its own try/catch and fall back to the original password for the handover bundle on failure. The sync room is encrypted and functional regardless of whether the password was rotated.

Bug 2: Hold the keepAlive link as a field (KeepAliveLink? _keepAliveLink) and release it in reset() (called when the modal closes) rather than in a finally block.

Verified

• matrix.org returns M_UNRECOGNIZED on POST /_matrix/client/v3/account/password (tested with curl against matrix-client.matrix.org)
• Code paths confirmed by reading provisioning_controller.dart, provisioned_config_page.dart, and matrix_sdk_gateway.dart

[matthiasn]

@overcuriousity thanks for reporting this. I'm running a Synapse server via https://etke.cc which works extremely well and I spent a lot of time getting it to this level of performance. I had at a previous stage built sync via IMAP and after spending all this time on sync, I can wholeheartedly say that I have very little appetite to consider another option for sync. File-based sync alone (also via Syncthing) would not help much because the whole system here is message-based where truth on each side converges in the respective local databases, and both systems can be online at the same time. Trying to sync the SQLite files here would not work.

I'm hesitant calling the lack of support for the required password endpoint in the matrix home server a bug in Lotti. I would rather frame it as that server being incompatible. After all, just skipping password rotation has a serious implication that Claude apparently missed or glossed over here:

• Password rotation guarantees that a provisioning bundle is a one-time token
• Whoever uses it first becomes the owner and sole maintainer of that account
• Without it, anyone else could join the same room as well
• When that happens, the room is effectively dead because any joiners would initiate the emoji confirmation flow where the same sequence must appear on all devices
• Either other users naïvely accept and share their data with those later joiner(s) or they don't and sync is bricked altogether, as Lotti refused to send anything to a room with unconfirmed devices
• All this cannot happen if the password is rotated on first use

Any Synapse server should support the endpoint unless intentionally disabled. Dendrite works too.

I was already thinking about offering to run sync as a service on top of these Etke server for a tiny fee to contribute to development costs, do you think that makes sense?

If you like, I can send you a provisioning profile running on my at this point mostly idle server if you'd like to become a test user for that (for free of course).

[overcuriousity]

@matthiasn Thanks for the clarification! I agree with your explanation, cant actually blame matrix.org for being incompatible - they just serve another usecase.
However, it might make sense to clarify in the docs, cause most people will try to use that first, if they arent self-hosting.
In general I find the idea to use Matrix for syncing incredibly creative and interesting, would be happy to test its performance, because that always was something I struggled with by running Synapse. If you want, feel free to mail me.
So also your idea to offer yoir etke.cc server for a fee seems fair totally. The only thing I personally wouldnt like, if it is advertised in the application directly - but thats just my opinion and up to you of course.