Application message in commit bundles

[pcapriotti]

Allow commit bundles to contain one application message. The message must be for the epoch after the commit, and it gets sent after the commit has been accepted.

https://wearezeta.atlassian.net/browse/WPB-20803

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[Copilot]

Pull request overview

This pull request adds support for commit bundles to contain an optional application message. The message must be for the epoch after the commit and is sent to all conversation members after the commit has been accepted.

Changes:

• Added appMessage field to CommitBundle and related data structures to support optional application messages
• Introduced ClientMap newtype wrapper with helper functions to improve type safety and encapsulation of client mapping operations
• Implemented validation and propagation logic for application messages in commit bundles, ensuring they are for the correct epoch and sent after commit acceptance

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
libs/wire-api/src/Wire/API/MLS/CommitBundle.hs	Added appMessage field to CommitBundle data structure and updated parsing/serialization logic
libs/wire-api/src/Wire/API/MLS/Message.hs	Added Arbitrary instances for Message types to support testing
libs/wire-subsystems/src/Wire/ConversationStore/MLS/Types.hs	Introduced ClientMap newtype wrapper with helper functions for safer client map operations
services/galley/src/Galley/API/MLS/Message.hs	Added validateMessage function and logic to handle application messages in commit bundles
services/galley/src/Galley/API/MLS/IncomingMessage.hs	Added appMessage field to IncomingBundle
services/galley/src/Galley/API/MLS/Propagate.hs	Updated propagateMessage signature to use generic ClientMap type parameter
services/galley/src/Galley/API/MLS/SubConversation.hs	Updated to use ClientMap helper functions
services/galley/src/Galley/API/MLS/Removal.hs	Updated to use ClientMap helper functions
services/galley/src/Galley/API/MLS/Proposal.hs	Simplified Semigroup instance to use derived behavior
services/galley/src/Galley/API/MLS/OutOfSync.hs	Updated to use unClientMap accessor
services/galley/src/Galley/API/MLS/Commit/InternalCommit.hs	Updated to use ClientMap helper functions
services/galley/src/Galley/API/MLS/CheckClients.hs	Updated to use ClientMap helper functions
services/galley/src/Galley/API/Internal.hs	Updated to use unClientMap accessor
services/galley/test/integration/API/MLS/Util.hs	Updated test utility to pass Nothing for appMessage field
libs/wire-api/test/unit/Test/Wire/API/Roundtrip/MLS.hs	Updated test to generate arbitrary appMessage values
integration/test/Test/MLS/History.hs	Added new integration test for commit bundles with application messages
integration/test/MLS/Util.hs	Updated MessagePackage with appMessage field and related functions
integration/integration.cabal	Registered new test module
changelog.d/2-features/mls-bundle-extra-messages	Added changelog entry documenting the feature

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