Privacy is capability-specific
Privacy keys and rules define permitted interactions, alongside global settings. Process synchronization updates after changes rather than modifying only a local switch. Messages from new contacts may be affected by Premium or paid-message settings.
A failed lookup does not prove non-registration
Contact import and phone lookup respect the target’s privacy settings. An unavailable result can mean either no account or a blocked lookup. Do not present it as definitive public evidence of registration status.
Blocklists have distinct scopes
The main and story blocklists are separate. Changes synchronize to the account’s other sessions; the blocked peer receives no corresponding system update. A support product requiring an explicit notice must implement its own appropriate communication flow.
Implementation recommendations
Upload contacts only with informed authorization. Define purpose and retention before storing them. Before replacing a blocklist, verify that the proposed set is complete; a partial page must not accidentally remove other restrictions.