Agents using API channel inboxes (e.g., WhatsApp Automate) reported
seeing the same conversation appear twice in their conversation list —
one showing the last message preview and the other showing "No
Messages". Backend investigation confirmed no duplicate conversations
exist in the database, making this purely a frontend issue.
The root cause is a race condition in WebSocket event delivery. When a
conversation is created via the API with auto-assignment, the backend
enqueues multiple ActionCable broadcast jobs (`conversation.created`,
`assignee.changed`, `team.changed`) within milliseconds of each other.
In production with multi-threaded Sidekiq workers, these events can
arrive at the frontend out of order. If `assignee.changed` arrives
before `conversation.created`, the `UPDATE_CONVERSATION` mutation pushes
the conversation into the store (since it doesn't exist yet), and then
`ADD_CONVERSATION` blindly pushes it again — resulting in a duplicate
entry.
The fix adds a uniqueness check in the `ADD_CONVERSATION` mutation to
skip the push if a conversation with the same ID already exists in the
store, matching the dedup pattern already used by
`SET_ALL_CONVERSATION`.
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