When the same person registers on multiple federated instances, separate
DM channels are created for each identity, causing duplicate sidebar
entries (e.g., "Nova" appearing twice — once for local, once for
federated account).
Add deduplicateDmChannels() safety net that detects matching counterparts
using two layers: canonicalUserMatch (same ID/homeUserId/username) and
replicatedInstances cross-check (local user has a replicated account on
the federated user's home instance with the same base username). Keeps
the DM with the most recent activity, applied in both setDmChannels and
populateFromReady.
Investigation: queried both live instances (nova.ddns.net, orbit)
and confirmed root cause is same-person-two-accounts, not a server-side
creation bug or identity resolution gap.
Jannis Braun
32d9647ed1