We've been seeing orphan conversations (conversations whose contact has
been deleted) on high-frequency accounts. These orphans cause 500 errors
when the API attempts to render conversation data, since the jbuilder
partials expect a valid contact association.
The `ProcessStaleContactsJob` triggers `RemoveStaleContactsService`,
which uses `delete_all` to remove contacts. While the query only selects
contacts without conversations, `delete_all` bypasses ActiveRecord
callbacks and does not re-verify at deletion time. We suspect this
creates a window where a new conversation can be created for a contact
between query evaluation and the actual delete, leaving the conversation
orphaned.
**This is unverified — disabling the job is the experiment to confirm or
rule out this theory.**
This PR disables the job for a monitoring period. If orphan
conversations stop appearing, we'll have confirmation and can work on a
proper fix for the service. If they continue, we'll investigate other
deletion paths.
Stale contacts will accumulate while the job is disabled, but this is a
controlled tradeoff — they are inert records with no user-facing impact,
and can be cleaned up in bulk once we re-enable or fix the job.
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