Fix a bug which could corrupt auth chains

[kegsay]

Complement tests

Basically, when we use /state_ids in conjunction with /event requests, the /event request can fail causing a partial state to be returned. When we persist the state, we process dependent events first. If we fail to process a dependent event due to missing the auth_event, we didn't update the in-memory event map. This meant that we could incorrectly persist events that depended on dropped events.

Discovered via Chaos testing.

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Code style is correct (run the linters)

[MadLittleMods]

Additionally, should check_state_independent_auth_rules even be using the full auth_map?

Feels like we should be constructing a subset map with just the event.auth_event_ids()

---

auth_events_for_event = []
auth_event_map_for_event = {}

Suggested change

	# Drop the event from the auth_map too, else we may incorrectly persist
	# events which depend on this dropped event.
	auth_map.pop(event.event_id, None)
	return
	auth.append(ae)
	# Drop the event from the auth_map too, else we may incorrectly persist
	# events which depend on this dropped event.
	auth_map.pop(event.event_id, None)
	return
	auth_events_for_event.append(ae)
	auth_event_map_for_event[auth_event_id] = ae

                    await check_state_independent_auth_rules(
                        self._store, event, batched_auth_events=auth_event_map_for_event
                    )
                    check_state_dependent_auth_rules(event, auth_events_for_event)