This field seems to be a left-over from the StatusNet era.
If your application uses `pleroma.conversation_id`: this field is
deprecated.
It is currently stubbed instead by doing a CRC32 of the context, and
clearing the MSB to avoid overflow exceptions with signed integers on
the different clients using this field (Java/Kotlin code, mostly; see
Husky and probably other mobile clients.)
This should be removed in a future version of Pleroma. Pleroma-FE
currently depends on this field, as well.
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