fix(llc, persistence): truncated channels sinking to the bottom of a last_updated sort

[VelikovPetar]

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Linear: FLU-689

Github Issue: #

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Description of the pull request

Backport of #2880 to v9 (merge commit 02ba6a239d8e0292729d9b6bd8e9d277e240fa57).

last_updated is not a wire field — every SDK derives it locally from last_message_at and created_at. Flutter derived it with a plain null-fallback:

DateTime get lastUpdatedAt => lastMessageAt ?? createdAt;

When a channel is truncated the server does not clear last_message_at — it sets it to a value older than created_at. Since the getter only falls back on null, it returned that stale date, so a truncated channel dropped to the bottom of a channel list sorted { last_updated: -1 } — below channels that had never been used at all. The default channel list sort is last_updated descending (StreamChannelListController, and the PredefinedFilter fallback), so this hits the default configuration on v9 exactly as it did on master.

Flutter was the only SDK without a guard here: Android's Channel.lastUpdated takes the max of the two dates, and iOS's ChannelDTO.defaultSortingAt has an explicit distantPast fallback naming the truncation case. This adopts Android's max() semantics, which covers any lastMessageAt < createdAt rather than just a sentinel value.

Changes

packages/stream_chat — ChannelModel.lastUpdatedAt now returns the later of the two dates. This is the value ChannelState.getComparableField(ChannelSortKey.lastUpdated) returns, so it fixes both the in-memory controller sort and the persistence comparator sort in one place. No behaviour change when last_message_at is newer or null.

packages/stream_chat_persistence — ChannelDao.cids ranked channels with ORDER BY last_message_at DESC LIMIT 250. That result feeds StreamChatClient.sync(), which requests events missed while offline, so a truncated channel was the first to fall out of the 250-channel cap and silently stopped receiving missed events (only reproducible with more than 250 cached channels). It now orders by a CASE WHEN expression mirroring the Dart getter.

Worth noting for review: this is a selection cutoff, not a presentation order. The offline queryChannels read path (ChannelQueryDao.getChannels) has no ORDER BY/LIMIT and applies the caller's SortOrder comparator in Dart, so the sort passed to queryChannels was always respected.

created_at is non-nullable in the Drift schema, so the CASE WHEN always resolves. No schema change and no migration.

Port notes

Manual port rather than a clean cherry-pick, for two reasons — neither changes behaviour relative to master:

• Formatting — v9 formats at the default 80 columns (master uses 120), so the DAO helper and the if-case guard wrap across more lines. The if (x case final x? when ...) construct is idiomatic on v9 (156 uses in the LLC) and valid on its ^3.6.2 SDK floor.
• drift ^2.22.1 — v9 pins an older drift than master's ^2.33.0. Verified against drift 2.22.1 directly: CaseWhenExpression({required cases, orElse}) and isBiggerThan have identical signatures there, so the DAO change is safe at v9's declared floor, not just at the resolved version.

CHANGELOG entries were added under a new ## Upcoming section in both packages, since v9's topmost section (## 9.27.0) is already released.

Tests

• ChannelModel.lastUpdatedAt — newer lastMessageAt wins, null falls back to createdAt, older (truncated) falls back to createdAt
• ChannelSortKey.lastUpdated via getComparableField — this key previously had no coverage at all
• ChannelDao.cids ordering — the existing cids test now saves three channels and asserts one ordering. It discriminates the fix: the old ORDER BY last_message_at DESC yields active, stale, truncated, the new expression yields active, truncated, stale

Verified on this branch: melos run format clean, dart analyze --fatal-infos clean on all touched files, full stream_chat suite passes (1307 tests, 2 skipped), full stream_chat_persistence suite passes (260 tests).

Also ran as a negative control: with only the two lib/ changes reverted, the new lastUpdatedAt test and the cids test both fail — confirming the ported tests are not passing vacuously.

Screenshots / Videos

No UI changes.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@          Coverage Diff          @@
##             v9    #2892   +/-   ##
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  Coverage      ?   67.32%           
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  Files         ?      431           
  Lines         ?    27401           
  Branches      ?        0           
=====================================
  Hits          ?    18448           
  Misses        ?     8953           
  Partials      ?        0           

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