- Faster joins: Refactor internal handling of servers in room to never store an empty list. ([\#14954](https://github.com/matrix-org/synapse/issues/14954))
- Faster joins: tag `v2/send_join/` requests to indicate if they served a partial join response. ([\#14950](https://github.com/matrix-org/synapse/issues/14950))
- Allow running `cargo` without the `extension-module` option. ([\#14965](https://github.com/matrix-org/synapse/issues/14965))
-Add denormalised event stream ordering column to membership state tables for future use. Contributed by Nick @ Beeper (@fizzadar). ([\#14979](https://github.com/matrix-org/synapse/issues/14979))
-Preparatory work for adding a denormalised event stream ordering column in the future. Contributed by Nick @ Beeper (@fizzadar). ([\#14979](https://github.com/matrix-org/synapse/issues/14979), [9cd7610](https://github.com/matrix-org/synapse/commit/9cd7610f86ab5051c9365dd38d1eec405a5f8ca6), [f10caa7](https://github.com/matrix-org/synapse/commit/f10caa73eee0caa91cf373966104d1ededae2aee); see [\#15014](https://github.com/matrix-org/synapse/issues/15014))
- Add tests for `_flatten_dict`. ([\#14981](https://github.com/matrix-org/synapse/issues/14981), [\#15002](https://github.com/matrix-org/synapse/issues/15002))
