Add MessageBufferingConfig to allow custom back-pressure config for message.new events

[VelikovPetar]

Goal

High-traffic channel types (e.g. livestreams) can produce a flood of message.new events that arrive faster than the sequential event-handling pipeline can process them. The current implementation funnels every socket event through a single MutableSharedFlow with extraBufferCapacity = Int.MAX_VALUE, which means there is no back-pressure: a burst of new-message events queues up unbounded memory and starves more important signals (reads, bans, member updates) of timely processing.

This PR introduces a MessageBufferConfig that lets integrators opt specific channel types into a bounded buffer for NewMessageEvents, with a configurable overflow strategy (SUSPEND / DROP_OLDEST / DROP_LATEST). Signal-critical events and events for non-opted-in channel types are unaffected.

Implementation

• Added MessageBufferConfig (under MessageLimitConfig.messageBufferConfig) exposing:
  • channelTypes: Set<String> — channel types whose NewMessageEvents go through the bounded buffer (empty by default → feature is a no-op).
  • capacity: Int — buffer capacity (defaults to Int.MAX_VALUE).
  • overflow: BufferOverflow — overflow strategy (defaults to SUSPEND).
• EventHandlerSequential now allocates a secondary MutableSharedFlow (bufferedNewMessageEvents) lazily, only when buffering is enabled, so the default configuration pays no cost for it.
• Two listener variants:
  • defaultSocketEventListener — the existing unbuffered path; used when no channel types are opted in.
  • bufferedSocketEventListener — routes NewMessageEvents for opted-in channel types to the bounded flow, and everything else (including non-opted-in NewMessageEvents and all other event types) to the unbuffered flow.
• startListening() picks the listener based on bufferConfig.channelTypes.isNotEmpty() and only collects from bufferedNewMessageEvents when buffering is enabled.
• StreamStatePluginFactory wires the config from StatePluginConfig.messageLimitConfig.messageBufferConfig into EventHandlerSequential.

The bounded flow shares the same downstream pipeline (socketEventCollector → handleBatchEvent) as the unbuffered flow, so ordering inside each flow is preserved and back-pressure is applied independently per flow.

Testing

• Added 200+ lines of unit tests in EventHandlerSequentialTest covering:
  • default behaviour (no buffering) is unchanged when channelTypes is empty.
  • NewMessageEvents for opted-in channel types are routed through the bounded buffer.
  • NewMessageEvents for non-opted-in channel types and all non-NewMessageEvent events keep using the unbuffered path.
  • DROP_OLDEST / DROP_LATEST / SUSPEND overflow strategies behave as expected when the buffer is full.
• Existing tests (TotalUnreadCountTest, EventHandlerSequentialUserMessagesDeletedTest) updated to pass the new bufferConfig argument.

[github-actions]

PR checklist ✅

All required conditions are satisfied:

• Title length is OK (or ignored by label).
• At least one pr: label exists.
• Sections ### Goal, ### Implementation, and ### Testing are filled.

🎉 Great job! This PR is ready for review.

[github-actions]

SDK Size Comparison 📏

SDK	Before	After	Difference	Status
stream-chat-android-client	5.26 MB	5.26 MB	0.00 MB	🟢
stream-chat-android-offline	5.49 MB	5.49 MB	0.00 MB	🟢
stream-chat-android-ui-components	10.64 MB	10.65 MB	0.00 MB	🟢
stream-chat-android-compose	12.87 MB	12.87 MB	0.00 MB	🟢

[sonarqubecloud]

Quality Gate failed

Failed conditions
76.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud