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.
30 to 70% of the objects in the object table are simple JSON objects
containing a single field, 'id', being the context's ID. The reason for
the creation of an object per context seems to be an old relic from the
StatusNet era, and has only been used nowadays as an helper for threads
in Pleroma-FE via the `pleroma.conversation_id` field in status views.
An object per context was created, and its numerical ID (table column)
was used and stored as 'context_id' in the object and activity along
with the full 'context' URI/string.
This commit removes this field and stops creation of objects for each
context, which will also allow incoming activities to use activity IDs
as contexts, something which was not possible before, or would have been
very broken under most circumstances.
The `pleroma.conversation_id` field has been reimplemented in a way to
maintain backwards-compatibility by calculating a CRC32 of the full
context URI/string in the object, instead of relying on the row ID for
the created context object.
