fix(llc): update watcher count from realtime events and ignore events after dispose

[VelikovPetar]

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Linear: FLU-619, FLU-658

Github Issue: #

CLA

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• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request

Backports two llc fixes from master to v9. They are independent; each is a separate commit.

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1. Watcher count / watchers from realtime events — FLU-619

Backport of master commit 84c6a24 (originally #2837).

Why

ChannelClientState.watcherCount and ChannelClientState.watchers never reflected realtime events during a session:

• The server's watcher_count on user.watching.start / user.watching.stop / message.new was dropped into Event.extraData, so the count stayed frozen at the last full channel.watch() / queryChannels snapshot.
• Watchers were never removed from watchers on user.watching.stop — the additive keyed merge in updateChannelState (needed for watcher pagination) can only upsert, so the departing watcher lingered until the next full query.

iOS and Android already trust the server-provided watcher_count per event, so Flutter was the outlier.

Changes

• Add Event.watcherCount, mapping the server watcher_count field (promoted to a first-class field instead of extraData).
• Apply the count on user.watching.start, user.watching.stop, and message.new.
• Remove the departing watcher from ChannelClientState.watchers on user.watching.stop (assign _channelState directly, bypassing the additive merge).

notification.message_new / notification.thread_message_new are intentionally excluded: the backend fetches the watcher count only after the notification fan-out, so these events structurally carry watcher_count: 0.

Port notes

Manual port, not a clean cherry-pick:

• Formatting — master formats at 120 cols; v9 uses the 80-col default, so every touched hunk needed rewrapping.
• Event.deletedForMe — a master-only field adjacent to the ported hunks in event.dart; not brought over.
• _listenMessageNew — master extracted this handler's body into addNewMessage, which does not exist on v9. The extracted body was verified byte-for-byte identical to v9's inline body, so the watcher-count block was appended at the equivalent point (after submitForDelivery).
• event.g.dart — regenerated with json_serializable pinned to 6.9.5. The currently-resolving 6.14.1 emits Dart 3.10 null-aware map elements ('key': ?instance.x), which v9's sdk: ^3.6.2 rejects. Output matches v9's existing if (instance.x case final value?) style. Note separately: this means melos run generate:dart is currently broken on v9 with an up-to-date toolchain, independent of this PR.

Performance note

The message.new handler's extra updateChannelState call is O(1), not a message-list walk: copyWith(watcherCount:) preserves the messages list reference, and merge short-circuits on identical(other, this). It does add one extra channelStateStream emission, in a path that already emits multiple times per message (updateMessage, then the unreadCount setter). Same shape and cost as on master.

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2. Ignore events dispatched after the client is disposed — FLU-658

Backport of master commit 4ba19d7 (originally #2855).

Why

StreamChatClient.handleEvent could throw StateError: Cannot add new events after calling close when the client was disposed while a reconnect recovery was still in flight.

_onConnectionStatusChanged is async. On an offline→online transition it awaits a recovery pipeline (sync / queryChannelsOnline) and only then emits the trailing connectionRecovered event, driven by a fire-and-forget subscription. If dispose() closes _eventController while that continuation is suspended on an await, the trailing handleEvent adds to a closed controller — surfacing as an unhandled async error.

Changes

Guard handleEvent against a closed controller (early return on isClosed, plus safeAdd).

Safety analysis on v9

Verified directly against the v9 sources rather than inherited from the master PR:

• _eventController.close() has a single call site, inside dispose().
• disconnectUser() closes the WS and resets state/credentials/persistence but leaves the event controller open, so the logout→login reuse path is unaffected — the guard cannot swallow events on a live or reused client.
• _eventController is a non-late final initialized inline and never reassigned, so isClosed is terminal for the client's lifetime.
• Post-close() the broadcast stream is already complete, so no subscriber could have received these events; the guard removes the throw, not a delivery.

Semantic equivalence with master, despite a controller-type divergence: master's _eventController is a master-only EventController<Event>, v9's is a PublishSubject<Event> — but both are rxdart Subject subclasses backed by a broadcast StreamController, so isClosed is the same inherited implementation (Subject.isClosed => _controller.isClosed) and safeAdd resolves to the same StreamControllerX extension on both. The controllers differ only in where the poll-vote→poll-answer normalization happens (master overrides EventController.add; v9 maps it in the eventStream getter), which is orthogonal to the guard.

Behaviour change worth naming (identical placement on master): because the guard precedes the health-check branch, a health.check arriving after dispose no longer runs _handleHealthCheckEvent. That is correct — disconnectUser() has by then reset the connection-id manager and closed the persistence connection, so those writes would target torn-down objects.

Port notes

The client.dart hunk applies cleanly (v9's handleEvent is byte-identical to master's pre-fix version). Two adaptations:

• v9's client.dart lacked import 'package:stream_chat/src/core/util/extension.dart' (master has it), so safeAdd did not resolve until it was added. This is the only line beyond master's diff.
• The test group is appended at the end of main(). Master inserts it before group('WS events'), which does not exist in v9's client_test.dart. import 'dart:async' was also added for Completer.

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Tests

FLU-619 — new Watching Events group in channel_test.dart: start/stop update the count, stop removes the watcher, a null count preserves the existing value, message.new updates the count, message.new without a count preserves it, and notification.message_new does not overwrite it.

Beyond the master commit, event_test.dart's existing parse / serialize / copyWith tests and test/fixtures/event.json were extended to cover watcher_count, following this repo's convention of extending existing serialization tests when adding model fields.

FLU-658 — new dispose during reconnect recovery group in client_test.dart, disposing the client while a recovery is suspended on a held-open queryChannels, then resuming it. Verified as a genuine regression test: with the guard reverted it fails with exactly Bad state: Cannot add new events after calling close; with the guard it passes.

Verification

• melos run format — clean (0 changed).
• melos run analyze — stream_chat: No issues found.
• Full stream_chat suite: 1309 pass, 2 skipped, 0 fail.

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    #2898   +/-   ##
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  Coverage      ?   67.39%           
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  Files         ?      431           
  Lines         ?    27417           
  Branches      ?        0           
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  Hits          ?    18477           
  Misses        ?     8940           
  Partials      ?        0           

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