core: fix races on member removal / delivery of their messages (#7010)

src/Simplex/Chat/Store/Postgres/Migrations/M20260525_member_removed_at.hs

@@ -0,0 +1,19 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+
+module Simplex.Chat.Store.Postgres.Migrations.M20260525_member_removed_at where
+
+import Data.Text (Text)
+import Text.RawString.QQ (r)
+
+m20260525_member_removed_at :: Text
+m20260525_member_removed_at =
+  [r|
+ALTER TABLE group_members ADD COLUMN removed_at TIMESTAMPTZ;
+|]
+
+down_m20260525_member_removed_at :: Text
+down_m20260525_member_removed_at =
+  [r|
+ALTER TABLE group_members DROP COLUMN removed_at;
+|]

src/Simplex/Chat/Store/Postgres/Migrations/chat_schema.sql

@@ -818,7 +818,8 @@ CREATE TABLE test_chat_schema.group_members (
     index_in_group bigint DEFAULT 0 NOT NULL,
     member_relations_vector bytea,
     relay_link bytea,
-    member_pub_key bytea
+    member_pub_key bytea,
+    removed_at timestamp with time zone
 );