ChatTransportEventCoordinator, ChatPeerIdentityCoordinator,
ChatMediaTransferCoordinator, ChatVerificationCoordinator, and
ChatLifecycleCoordinator drop their unowned ChatViewModel back-refs for
narrow @MainActor contexts (20-36 members each), reusing shared
witnesses across protocols. The two remaining raw writers of
sentReadReceipts now route through owner intent ops
(unmarkReadReceiptsSent, syncReadReceiptsForSentMessages), closing the
gaps noted in the previous commit. NoiseEncryptionService stays fully
out of the verification coordinator via installNoiseSessionCallbacks.
26 new mock-context tests.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
