Design: Leave & Stop-Forward (m9-leave-revocation)

Architecture

Backend-only. No UI changes. Touches 6 files.

Storage

Tag::CommunityLeave = 0x11 added to storage/keys.rs (after PurgeManifest = 0x10).

Key format: encode_key(EntityId::new(user_id), Tag::CommunityLeave, b"") — no suffix.

Value format: [status: 1 byte (0=Active, 1=Left)][left_at_ns: 8 bytes LE] — fixed 9 bytes.

Stored in the users storage partition via storage.users_engine().

Data Types (entities/community.rs)

Appended to existing CommunityMembershipIndex:

pub enum MembershipStatus { Active, Left }
pub struct CommunityMembership { user_id, status, left_at_ns: Option<u64> }
pub fn serialize_membership(m: &CommunityMembership) -> [u8; 9]
pub fn deserialize_membership(user_id: u64, bytes: &[u8]) -> Option<CommunityMembership>

TidalDb Field (db/mod.rs)

community_leave_status: dashmap::DashMap<u64, crate::entities::CommunityMembership>,

Added after community_membership. Initialized to DashMap::new() in both from_config and from_parts.

API (db/community.rs)

Three new public methods appended to the existing TidalDb impl:

leave_community_layer(user_id) — creates Left membership, persists, inserts into DashMap
rejoin_community_layer(user_id) — creates Active membership (preserving left_at_ns), persists, inserts
community_layer_status(user_id) — reads from DashMap, returns default_active if absent
persist_leave_record(membership) — private helper: writes to users_engine via Tag::CommunityLeave

Gate (db/signals.rs)

Added to BOTH try_cohort_attribution and try_community_forwarding:

if self.community_leave_status.get(&user_id)
    .map_or(false, |m| m.status == MembershipStatus::Left)
{
    return;
}

Placed at top of each function before any other work.

Startup Restore (db/state_rebuild.rs)

rebuild_community_leave_status(storage, map) scans users_engine for Tag::CommunityLeave keys, deserializes each, inserts into DashMap. Called from from_parts after rebuild_community_memberships.

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