diff --git a/crates/chattyness-db/src/queries/memberships.rs b/crates/chattyness-db/src/queries/memberships.rs
index 212fe1e..cff70c6 100644
--- a/crates/chattyness-db/src/queries/memberships.rs
+++ b/crates/chattyness-db/src/queries/memberships.rs
@@ -35,12 +35,30 @@ pub async fn get_user_membership(
 }
 
 /// Create a new membership (join a realm).
+/// This function is idempotent - if the membership already exists, it returns the existing id.
 pub async fn create_membership(
     pool: &PgPool,
     user_id: Uuid,
     realm_id: Uuid,
     role: RealmRole,
 ) -> Result<Uuid, AppError> {
+    // Check if membership already exists
+    let existing: Option<(Uuid,)> = sqlx::query_as(
+        r#"
+        SELECT id FROM realm.memberships
+        WHERE user_id = $1 AND realm_id = $2
+        "#,
+    )
+    .bind(user_id)
+    .bind(realm_id)
+    .fetch_optional(pool)
+    .await?;
+
+    if let Some((id,)) = existing {
+        return Ok(id);
+    }
+
+    // Create new membership
     let (membership_id,): (Uuid,) = sqlx::query_as(
         r#"
         INSERT INTO realm.memberships (realm_id, user_id, role)
@@ -54,7 +72,7 @@ pub async fn create_membership(
     .fetch_one(pool)
     .await?;
 
-    // Update member count on the realm
+    // Only increment count for new memberships
     sqlx::query("UPDATE realm.realms SET member_count = member_count + 1 WHERE id = $1")
         .bind(realm_id)
         .execute(pool)
@@ -64,12 +82,30 @@ pub async fn create_membership(
 }
 
 /// Create a new membership using a connection (for RLS support).
+/// This function is idempotent - if the membership already exists, it returns the existing id.
 pub async fn create_membership_conn(
     conn: &mut sqlx::PgConnection,
     user_id: Uuid,
     realm_id: Uuid,
     role: RealmRole,
 ) -> Result<Uuid, AppError> {
+    // Check if membership already exists
+    let existing: Option<(Uuid,)> = sqlx::query_as(
+        r#"
+        SELECT id FROM realm.memberships
+        WHERE user_id = $1 AND realm_id = $2
+        "#,
+    )
+    .bind(user_id)
+    .bind(realm_id)
+    .fetch_optional(&mut *conn)
+    .await?;
+
+    if let Some((id,)) = existing {
+        return Ok(id);
+    }
+
+    // Create new membership
     let (membership_id,): (Uuid,) = sqlx::query_as(
         r#"
         INSERT INTO realm.memberships (realm_id, user_id, role)
@@ -83,7 +119,7 @@ pub async fn create_membership_conn(
     .fetch_one(&mut *conn)
     .await?;
 
-    // Update member count on the realm
+    // Only increment count for new memberships
     sqlx::query("UPDATE realm.realms SET member_count = member_count + 1 WHERE id = $1")
         .bind(realm_id)
         .execute(&mut *conn)
diff --git a/crates/chattyness-user-ui/src/api/auth.rs b/crates/chattyness-user-ui/src/api/auth.rs
index beb3757..e776ce0 100644
--- a/crates/chattyness-user-ui/src/api/auth.rs
+++ b/crates/chattyness-user-ui/src/api/auth.rs
@@ -368,6 +368,7 @@ pub async fn signup(
 /// Creates a real user account with the 'guest' tag. Guests are regular users
 /// with limited capabilities (no prop pickup, etc.) that can be reaped after 24 hours.
 pub async fn guest_login(
+    rls_conn: crate::auth::RlsConn,
     State(pool): State<PgPool>,
     session: Session,
     Json(req): Json<GuestLoginRequest>,
@@ -393,6 +394,17 @@ pub async fn guest_login(
     // Create guest user (no password) - trigger creates avatar automatically
     let user_id = users::create_guest_user(&pool, &guest_name).await?;
 
+    // Set RLS context to the new guest user for membership creation
+    rls_conn
+        .set_user_id(user_id)
+        .await
+        .map_err(|e| AppError::Internal(format!("Failed to set RLS context: {}", e)))?;
+
+    // Create membership for the guest so their position can be persisted
+    let mut conn = rls_conn.acquire().await;
+    memberships::create_membership_conn(&mut *conn, user_id, realm.id, RealmRole::Member).await?;
+    drop(conn);
+
     // Set up tower session (same as regular user login)
     session
         .insert(SESSION_USER_ID_KEY, user_id)