fix(llc): Don't upsert out-of-window messages on message.updated/message.deleted events

[VelikovPetar]

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Linear: FLU-560

Github Issue: #

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• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request

Backport of #2794 (FLU-560) from master to v9.

message.updated and soft message.deleted events were being unconditionally upserted into ChannelState.messages (and thread reply lists). When the target message wasn't in the currently loaded window — e.g. it lived on an older page the client hadn't paged in yet — this created a phantom entry in the sorted list, leaving a visible gap between the loaded slice and history.

Manual port (not a clean cherry-pick)

The original master change lives on bug/FLU-560_fix_message_updated_event_inserting_messages (earliest commit 9f39525). It could not be cherry-picked: master's updateMessage/deleteMessage were refactored into an _updateMessages / _updateThreadMessages / _mergeMessagesIntoExisting family that doesn't exist on v9, where these methods are still monolithic. The same intent was re-implemented against the v9 architecture.

What changed on v9

• _listenMessageUpdated (which on v9 also handles reaction.updated) now passes upsert: false.
• ChannelClientState.updateMessage gains a {bool upsert = true} flag. With upsert: false, an out-of-window message (id not already in messages) is not inserted into the sorted list, but pinned-message maintenance still runs.
• deleteMessage's soft-delete path now uses upsert: false (hard deletes are unchanged). Since the public deleteMessage also backs the optimistic delete flow, two existing optimistic-delete tests were updated to seed the message first.
• ChannelClientState.updateThreadInfo gains a {bool upsert = true} flag that guards against creating a phantom threads[parentId] entry for a thread that was never paged in, and against inserting unknown replies into a loaded thread.

The guard is id-based and independent of isUpToDate — even at the latest page we may have paginated past older history and receive an event for a message no longer in memory.

Tests

Ported the applicable coverage from #2794:

• New ChannelClientState.updateMessage group (upsert true/false, in-window update).
• messageUpdated → "outside loaded window": no phantom insert, out-of-window pin still lands, unknown reply not inserted into a thread, no phantom thread entry.
• New messageDeleted group: soft delete doesn't insert a phantom record, in-window soft delete marks as deleted, hard delete is a no-op out of window.

Three tests from the master PR were skipped because the underlying features don't exist on v9: the two activeLiveLocations tests (no live-location feature on v9) and the _pinIsValid unpin test (no _pinIsValid on v9).

Full stream_chat suite passes locally.

Screenshots / Videos

No UI changes.

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[codecov]

Codecov Report

❌ Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (v9@4a7ca7a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
packages/stream_chat/lib/src/client/channel.dart	94.28%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##             v9    #2815   +/-   ##
=====================================
  Coverage      ?   66.91%           
=====================================
  Files         ?      430           
  Lines         ?    27143           
  Branches      ?        0           
=====================================
  Hits          ?    18162           
  Misses        ?     8981           
  Partials      ?        0           

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